Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DQ and I-A; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of human histocompatibility antigen (HLA) DQ and mouse I-A. Three genetically distinct isotypes of class II MHC molecules are found in humans (HLA-DR, HLA-DQ, and HLA-DP), and two in mice (I-E and I-A). I-A and I-E have the same basic features insofar as peptide loading and presentation, they differ in that each interacts with distinctly different sets of peptides, and in the incidence of deletion of their genes. A structural understanding of the similarities and differences between I-A and I-E may help with understanding their roles in peptide presentation and T cell activation. Mouse I-Ag7 has a genetic susceptibility to autoimmune diabetes due to its small, uncharged amino acid residue at position 57 of their beta chain which results in the absence of a salt bridge between beta 57 and Arg alpha 76, which is adjacent to the P9 pocket of the peptide-binding groove. Human HLA-DR, -DQ, and -DP are about 70% similar to each other. HLA-DQ (DQ) is a cell surface receptor protein found on antigen presenting cells. It is an alphabeta heterodimer of type MHC class II. The alpha and beta chains are encoded by two loci, HLA-DQA1 and HLA-DQB1, that are adjacent to each other on chromosome band 6p21.3. A person often produces two alpha-chain and two beta chain variants and thus 4 isoforms of DQ. HLA-DQ is involved in the autoimmune diseases celiac disease and diabetes mellitus type. DQ is one of several antigens involved in rejection of organ transplants. DQ2 is encoded by the HLA-DQB1*02 allele group. DQ6 is encoded by the HLA-DQB1*06 allele group. DQ2 beta-chains combine with alpha-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. These isoforms, nicknamed DQ2.2 and DQ2.5, are also encoded by the DQA1*0201 and DQA1*0501 genes, respectively. DQ6 beta-chains combine with alpha-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. For DQ6, however, cis-isoform pairing only occurs with DQ1 alpha-chains. There are many haplotypes of DQ6. Susceptibility to Leptospirosis infection was found associated with undifferentiated DQ6. DQ8 is determined by the antibody recognition of beta8 and this generally detects the gene product of DQB1*0302. DQ8 is commonly linked to autoimmune disease in the human population. DQ8 is the second most predominant isoform linked to celiac disease and the DQ most linked to Type 1 diabetes. DQ8 increases the risk for rheumatoid arthritis and is linked to the primary risk locus for RA, HLA-DR4. DR4 also plays an important role in Type 1 diabetes. DQ8 is a split antigen of the DQ3 broad antigen. MHC class II molecules play a key role in the initiation of the antigen-specific immune response. They are expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice, and induced in nonprofessional APCs, such as keratinocyctes; they are expressed on the surface of activated human T cells and on T cells from other species. MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes; these peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC, and bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 126 RVEPTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTC 205
Cdd:cd21001    1 RVEPTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTC 80

                         90
                 ....*....|....*..
gi 345461081 206 HVEHPSLQSPITVEWRA 222
Cdd:cd21001   81 HVEHPSLQSPITVEWRA 97

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DQ and I-A; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of human histocompatibility antigen (HLA) DQ and mouse I-A. Three genetically distinct isotypes of class II MHC molecules are found in humans (HLA-DR, HLA-DQ, and HLA-DP), and two in mice (I-E and I-A). I-A and I-E have the same basic features insofar as peptide loading and presentation, they differ in that each interacts with distinctly different sets of peptides, and in the incidence of deletion of their genes. A structural understanding of the similarities and differences between I-A and I-E may help with understanding their roles in peptide presentation and T cell activation. Mouse I-Ag7 has a genetic susceptibility to autoimmune diabetes due to its small, uncharged amino acid residue at position 57 of their beta chain which results in the absence of a salt bridge between beta 57 and Arg alpha 76, which is adjacent to the P9 pocket of the peptide-binding groove. Human HLA-DR, -DQ, and -DP are about 70% similar to each other. HLA-DQ (DQ) is a cell surface receptor protein found on antigen presenting cells. It is an alphabeta heterodimer of type MHC class II. The alpha and beta chains are encoded by two loci, HLA-DQA1 and HLA-DQB1, that are adjacent to each other on chromosome band 6p21.3. A person often produces two alpha-chain and two beta chain variants and thus 4 isoforms of DQ. HLA-DQ is involved in the autoimmune diseases celiac disease and diabetes mellitus type. DQ is one of several antigens involved in rejection of organ transplants. DQ2 is encoded by the HLA-DQB1*02 allele group. DQ6 is encoded by the HLA-DQB1*06 allele group. DQ2 beta-chains combine with alpha-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. These isoforms, nicknamed DQ2.2 and DQ2.5, are also encoded by the DQA1*0201 and DQA1*0501 genes, respectively. DQ6 beta-chains combine with alpha-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. For DQ6, however, cis-isoform pairing only occurs with DQ1 alpha-chains. There are many haplotypes of DQ6. Susceptibility to Leptospirosis infection was found associated with undifferentiated DQ6. DQ8 is determined by the antibody recognition of beta8 and this generally detects the gene product of DQB1*0302. DQ8 is commonly linked to autoimmune disease in the human population. DQ8 is the second most predominant isoform linked to celiac disease and the DQ most linked to Type 1 diabetes. DQ8 increases the risk for rheumatoid arthritis and is linked to the primary risk locus for RA, HLA-DR4. DR4 also plays an important role in Type 1 diabetes. DQ8 is a split antigen of the DQ3 broad antigen. MHC class II molecules play a key role in the initiation of the antigen-specific immune response. They are expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice, and induced in nonprofessional APCs, such as keratinocyctes; they are expressed on the surface of activated human T cells and on T cells from other species. MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes; these peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC, and bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 126 RVEPTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTC 205
Cdd:cd21001    1 RVEPTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTC 80

                         90
                 ....*....|....*..
gi 345461081 206 HVEHPSLQSPITVEWRA 222
Cdd:cd21001   81 HVEHPSLQSPITVEWRA 97

Class II histocompatibility antigen, beta domain; Class II MHC glycoproteins are expressed on the surface of antigen-presenting cells (APC), including macrophages, dendritic cells and B cells. MHC II proteins present peptide antigens that originate extracellularly from foreign bodies such as bacteria. Proteins from the pathogen are degraded into peptide fragments within the APC, which sequesters these fragments into the endosome so they can bind to MHC class II proteins, before being transported to the cell surface. MHC class II receptors display antigens for recognition by helper T cells (stimulate development of B cell clones) and inflammatory T cells (cause the release of lymphokines that attract other cells to site of infection).

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|..
gi 345461081    45 GMCYFTNGTERVRLVTRYIYNREEYARFDSDVGVYRAVTPQGRPDAEYWNSQKEVLEGTRAELDTVCRHNYE 116
Cdd:smart00921   1 SECYFSNGTEDVRYVVRYIYNKEELVRFDSDVGKFVAFTELGRPAAEYWNSQKDLLERLRAEVDTVCRHNYQ 72

Immunoglobulin C-Type;

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 345461081   144 HNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEM---TPQRGDVYTCHVEHPSLQSP 215
Cdd:smart00407   1 KATLVCLVSGFYPPDITVTWLRNGQEVTEGVSTTDPLKNSDGTYFLSSYLTVpasTWESGDVYTCQVTHEGLKEP 75

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DQ and I-A; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of human histocompatibility antigen (HLA) DQ and mouse I-A. Three genetically distinct isotypes of class II MHC molecules are found in humans (HLA-DR, HLA-DQ, and HLA-DP), and two in mice (I-E and I-A). I-A and I-E have the same basic features insofar as peptide loading and presentation, they differ in that each interacts with distinctly different sets of peptides, and in the incidence of deletion of their genes. A structural understanding of the similarities and differences between I-A and I-E may help with understanding their roles in peptide presentation and T cell activation. Mouse I-Ag7 has a genetic susceptibility to autoimmune diabetes due to its small, uncharged amino acid residue at position 57 of their beta chain which results in the absence of a salt bridge between beta 57 and Arg alpha 76, which is adjacent to the P9 pocket of the peptide-binding groove. Human HLA-DR, -DQ, and -DP are about 70% similar to each other. HLA-DQ (DQ) is a cell surface receptor protein found on antigen presenting cells. It is an alphabeta heterodimer of type MHC class II. The alpha and beta chains are encoded by two loci, HLA-DQA1 and HLA-DQB1, that are adjacent to each other on chromosome band 6p21.3. A person often produces two alpha-chain and two beta chain variants and thus 4 isoforms of DQ. HLA-DQ is involved in the autoimmune diseases celiac disease and diabetes mellitus type. DQ is one of several antigens involved in rejection of organ transplants. DQ2 is encoded by the HLA-DQB1*02 allele group. DQ6 is encoded by the HLA-DQB1*06 allele group. DQ2 beta-chains combine with alpha-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. These isoforms, nicknamed DQ2.2 and DQ2.5, are also encoded by the DQA1*0201 and DQA1*0501 genes, respectively. DQ6 beta-chains combine with alpha-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. For DQ6, however, cis-isoform pairing only occurs with DQ1 alpha-chains. There are many haplotypes of DQ6. Susceptibility to Leptospirosis infection was found associated with undifferentiated DQ6. DQ8 is determined by the antibody recognition of beta8 and this generally detects the gene product of DQB1*0302. DQ8 is commonly linked to autoimmune disease in the human population. DQ8 is the second most predominant isoform linked to celiac disease and the DQ most linked to Type 1 diabetes. DQ8 increases the risk for rheumatoid arthritis and is linked to the primary risk locus for RA, HLA-DR4. DR4 also plays an important role in Type 1 diabetes. DQ8 is a split antigen of the DQ3 broad antigen. MHC class II molecules play a key role in the initiation of the antigen-specific immune response. They are expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice, and induced in nonprofessional APCs, such as keratinocyctes; they are expressed on the surface of activated human T cells and on T cells from other species. MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes; these peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC, and bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 126 RVEPTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTC 205
Cdd:cd21001    1 RVEPTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTC 80

                         90
                 ....*....|....*..
gi 345461081 206 HVEHPSLQSPITVEWRA 222
Cdd:cd21001   81 HVEHPSLQSPITVEWRA 97

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DP; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DP. HLA class II histocompatibility antigen, DP(W2) beta chain is a protein that in humans is encoded by the HLA-DPB1 gene. It plays a central role in the immune system by presenting peptides derived from extracellular proteins. MHC class II molecules are encoded by three different loci, HLA-DR, -DQ, and -DP, which are about 70% similar to each other. HLA-DP is an alphabeta heterodimer cell-surface receptor. Each DP subunit (alpha-subunit, beta-subunit) is composed of a alpha-helical N-terminal domain, an IgG-like beta sheet, a membrane spanning domain, and a cytoplasmic domain. The alpha-helical domain forms the sides of the peptide binding groove. The beta sheet regions form the base of the binding groove and the bulk of the molecule as well as the inter-subunit (non-covalent) binding region. Individuals carrying the MHCII allele, HLA-DP2, are at risk for chronic beryllium disease (CBD), a debilitating inflammatory lung condition caused by the reaction of CD4 T cells to inhaled beryllium. MHC class II molecules play a key role in the initiation of the antigen-specific immune reponse. These molecules have been shown to be expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice. The expression of these molecules has been shown to be induced in nonprofessional APCs such as keratinocyctes, and they are expressed on the surface of activated human T cells and on T cells from other species. The MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes. These peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC. These peptides bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 126 RVEPTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTC 205
Cdd:cd21003    1 RVQPKVNVSPSKKGPLQHHNLLVCHVTDFYPGNIQVRWFLNGQEETAGVVSTNLIHNGDWTFQILVMLEMTPQQGDVYTC 80

                         90
                 ....*....|....*.
gi 345461081 206 HVEHPSLQSPITVEWR 221
Cdd:cd21003   81 QVEHPSLDSPVTVEWK 96

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) I-E; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) I-E. Three genetically distinct isotypes of class II MHC molecules are found in humans (HLA-DR, HLA-DQ, and HLA-DP), and two in mice (I-E and I-A). I-A and I-E molecules have the same basic features insofar as peptide loading and presentation, although each interacts with distinctly different sets of peptides. They also differ in that there is a relatively high incidence of deletion of the I-E gene in both inbred strains of mice as well as wild mice and the lack of the reverse situation i.e. the deletion of I-A genes. A detailed structural understanding of the similarities and differences between I-A and the paralogous I-E could help illuminate the respective roles these molecules play in peptide presentation and T cell activation. Mouse I-Ag7 has a genetic susceptibility to autoimmune diabetes due to its small, uncharged amino acid residue at position 57 of their beta chain which results in the absence of a salt bridge between beta 57 and Arg alpha 76, which is adjacent to the P9 pocket of the peptide-binding groove. MHC class II molecules play a key role in the initiation of the antigen-specific immune reponse. These molecules have been shown to be expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice. The expression of these molecules has been shown to be induced in nonprofessional APCs such as keratinocyctes, and they are expressed on the surface of activated human T cells and on T cells from other species. The MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes. These peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC. These peptides bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 125 RRVEPTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYT 204
Cdd:cd20998    3 RRVEPTVTVYPTKTQPLEHHNLLVCSVSDFYPGNIEVRWFRNGKEEKTGIVSTGLVRNGDWTFQTLVMLETVPQSGEVYT 82

                         90
                 ....*....|....*..
gi 345461081 205 CHVEHPSLQSPITVEWR 221
Cdd:cd20998   83 CQVEHPSLTDPVTVEWK 99

Class II histocompatibility antigen, beta domain; Class II MHC glycoproteins are expressed on the surface of antigen-presenting cells (APC), including macrophages, dendritic cells and B cells. MHC II proteins present peptide antigens that originate extracellularly from foreign bodies such as bacteria. Proteins from the pathogen are degraded into peptide fragments within the APC, which sequesters these fragments into the endosome so they can bind to MHC class II proteins, before being transported to the cell surface. MHC class II receptors display antigens for recognition by helper T cells (stimulate development of B cell clones) and inflammatory T cells (cause the release of lymphokines that attract other cells to site of infection).

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|..
gi 345461081    45 GMCYFTNGTERVRLVTRYIYNREEYARFDSDVGVYRAVTPQGRPDAEYWNSQKEVLEGTRAELDTVCRHNYE 116
Cdd:smart00921   1 SECYFSNGTEDVRYVVRYIYNKEELVRFDSDVGKFVAFTELGRPAAEYWNSQKDLLERLRAEVDTVCRHNYQ 72

Immunoglobulin Constant-1 (C1)-set domain; The members here are composed of C1-set domains, classical Ig-like domains resembling the antibody constant domain. Members of the IgC1 family are components of immunoglobulin, T-cell receptors, CD1 cell surface glycoproteins, secretory glycoproteins A/C, and major histocompatibility complex (MHC) class I/II molecules. In immunoglobulins, each chain is composed of one variable domain (IgV) and one or more IgC domains. These names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. The IgV domain is responsible for antigen binding, while the IgC domain is involved in oligomerization and molecular interactions. The structures in C1-set are smaller than those in the V-set; they have one beta sheet that is formed by strands A, B, E, and D and the other strands by G, F, C, and C'.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 130 TVTIS-PSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQ---RGDVYTC 205
Cdd:cd00098    1 TVTLLpPSPEEKGGGKVTLVCLVSGFYPKDITVTWLKNGVPLTSGVSTSSPVEPNDGTYSVTSSLTVPPSdwdEGATYTC 80

                         90
                 ....*....|....*
gi 345461081 206 HVEHPSLQSPITVEW 220
Cdd:cd00098   81 VVTHESLKSPLSKTW 95

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DM; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DM. Human HLA-DM plays a critical role in antigen presentation to CD4 T cells by catalyzing the exchange of peptides bound to MHC class II molecules. Type 1 diabetes is correlated with DM activation and it is also implicated in viral infections such as herpes simplex virus, celiac disease, multiple sclerosis, other autoimmune diseases, and leukemia. MHC class II molecules play a key role in the initiation of the antigen-specific immune reponse. These molecules have been shown to be expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice. The expression of these molecules has been shown to be induced in nonprofessional APCs such as keratinocyctes, and they are expressed on the surface of activated human T cells and on T cells from other species. The MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes. These peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC. These peptides bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 126 RVEPTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQ----EETAGVVSTPlirNGDWTFQILVMLEMTPQRGD 201
Cdd:cd21002    1 RRPPSVRVAPTTPFNTREPVMLACHVWGFYPADVTITWLKNGDpvapHSSAPKTAQP---NGDWTYQTQVTLAVTPSPGD 77

                         90       100
                 ....*....|....*....|
gi 345461081 202 VYTCHVEHPSLQSPITVEWR 221
Cdd:cd21002   78 TYTCSVQHASLPEPLLEDWT 97

Class II major histocompatibility complex (MHC) alpha chain immunoglobulin domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) domain of the major histocompatibility complex (MHC) class II alpha chain. MHC class II molecules play a key role in the initiation of the antigen-specific immune reponse. These molecules have been shown to be expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice. The expression of these molecules has been shown to be induced in nonprofessional APCs such as keratinocyctes, and they are also expressed on the surface of activated human T cells and on T cells from other species. The MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes. These peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC. These peptides bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 127 VEPTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTCH 206
Cdd:cd05767    1 VPPEVTVFPKSPVELGEPNTLICFVDNFFPPVINVTWLRNGQPVTDGVSETVFLPREDHSFRKFSYLPFTPSEGDIYDCR 80

                         90
                 ....*....|....
gi 345461081 207 VEHPSLQSPITVEW 220
Cdd:cd05767   81 VEHWGLEEPLLKHW 94

Immunoglobulin domain of Zn-alpha2-glycoprotein (ZAG); member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin domain of Zn-alpha2-glycoprotein (ZAG). ZAG is a soluble protein that is present in serum and other body fluids. ZAG stimulates lipid degradation in adipocytes and causes the extensive fat losses associated with some advanced cancers. The 2.8 angstrom crystal structure of ZAG resembles a class I major histocompatibility complex (MHC) heavy chain, but ZAG does not bind the class I light chain beta-2-microglobulin. The ZAG structure includes a large groove analogous to class I MHC peptide binding grooves. Instead of a peptide, the ZAG groove contains a nonpeptidic compound that may be implicated in lipid catabolism under normal or pathological conditions. IgC_MHC_I_alpha3; Immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class I alpha chain. Class I MHC proteins bind antigenic peptide fragments and present them to CD8+ T lymphocytes. Class I molecules consist of a transmembrane alpha chain and a small chain called the beta-2-microglobulin. The alpha chain contains three extracellular domains, two of which fold together to form the peptide-binding cleft (alpha1 and alpha2), and one which has an Ig fold (alpha3). Peptide binding to class I molecules occurs in the endoplasmic reticulum (ER) and involves both chaperones and dedicated factors to assist in peptide loading. Class I MHC molecules are expressed on most nucleated cells.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 125 RRVEPTVTISpsRTEALNHHNLLVCSVTDFYPGQIKVRWFRND--QEETAGVVSTPlirNGDWTFQILVMLEMTPQRGDV 202
Cdd:cd21010    1 RQDPPSVSVT--SHVAPGKNRTLKCLAYDFYPRGISLHWTRAGkvQESESGGDVLP---SGNGTYQSWVVVEVPPQDRAP 75

                         90
                 ....*....|....*...
gi 345461081 203 YTCHVEHPSLQSPITVEW 220
Cdd:cd21010   76 YSCHVEHSSLAQPLTVPW 93

Class I major histocompatibility complex (MHC) alpha chain, alpha3 immunoglobulin domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class I alpha chain. Class I MHC proteins bind antigenic peptide fragments and present them to CD8+ T lymphocytes. Class I molecules consist of a transmembrane alpha chain and a small chain called the beta-2-microglobulin. The alpha chain contains three extracellular domains, two of which fold together to form the peptide-binding cleft (alpha1 and alpha2), and one which has an Ig fold (alpha3). Peptide binding to class I molecules occurs in the endoplasmic reticulum (ER) and involves both chaperones and dedicated factors to assist in peptide loading. Class I MHC molecules are expressed on most nucleated cells.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 345461081 147 LVCSVTDFYPGQIKVRWFRN--DQEETAGVVST-PlirNGDWTFQILVMLEMTPQRGDVYTCHVEHPSLQSPITVEW 220
Cdd:cd07698   19 LRCWALGFYPAEITLTWQRDgeDQTQDMELVETrP---NGDGTFQKWAAVVVPSGEEQRYTCHVQHEGLPEPLTLRW 92

Immunoglobulin light chain Constant domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) light chain constant (C) domain. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. In Ig, each chain is composed of one variable domain (IgV) and one or more constant domains (IgC); these names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. There are five types of heavy chains (alpha, gamma, delta, epsilon, and mu), which determine the type of immunoglobulin: IgA, IgG, IgD, IgE, and IgM, respectively. In higher vertebrates, there are two types of light chain, designated kappa and lambda, which seem to be functionally identical, and can associate with any of the heavy chains.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 128 EPTVTISPSRTEALNHHNL-LVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGD---VY 203
Cdd:cd07699    1 APSVTIFPPSSEELSSGKAtLVCLINKFYPGFATVTWKVDGSTVSSGVTTSKTEQQSDNTYSMSSYLTLSSSDWNkhkVY 80

                         90
                 ....*....|....
gi 345461081 204 TCHVEHPSLQSPIT 217
Cdd:cd07699   81 TCEVTHEGLSSTIT 94

Tapasin-R immunoglobulin-like domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin-like domain on Tapasin-R. Tapasin is a V-C1 (variable-constant) immunoglobulin superfamily molecule present in the endoplasmic reticulum (ER), where it links MHC class I molecules to the transporter associated with antigen processing (TAP). Tapasin-R is a tapasin-related protein that contains similar structural motifs to Tapasin, with some marked differences, especially in the V domain, transmembrane and cytoplasmic regions. The majority of Tapasin-R is located within the ER; however, there may be some expression of Tapasin-R at the cell surface. Tapasin-R lacks an obvious ER retention signal.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 129 PTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETA------GVVSTPLIRNGDWTFQI---LVMLEMTPQR 199
Cdd:cd05771    1 PRVRLSPKNLVKPDLPQTLSCHIAGYYPLDVDVEWLREEPGGSEsqvsrdGVSLSSHRQSVDGTYSIssyLTLEPGTENR 80

                         90
                 ....*....|....*....
gi 345461081 200 GDVYTCHVEHPSLQSPITV 218
Cdd:cd05771   81 GATYTCRVTHVSLEEPLSV 99

Class II major histocompatibility complex (MHC) alpha chain immunoglobulin domain of histocompatibility antigen (HLA) I-E; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class II alpha chain of histocompatibility antigen (HLA) I-E. MHC class II molecules play a key role in the initiation of the antigen-specific immune reponse. These molecules have been shown to be expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice. The expression of these molecules has been shown to be induced in nonprofessional APCs such as keratinocyctes, and they are expressed on the surface of activated human T cells and on T cells from other species. The MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes. These peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC. These peptides bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 127 VEPTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTCH 206
Cdd:cd21005    1 VAPEVTVLSRSPVNLGEPNILICFIDKFSPPVVNVTWLRNGRPVTEGVSETVFLPRDDHLFRKFHYLTFLPSTDDFYDCE 80

                         90
                 ....*....|....
gi 345461081 207 VEHPSLQSPITVEW 220
Cdd:cd21005   81 VDHWGLEEPLRKHW 94

CH3 domain (third constant Ig domain of the heavy chain) in immunoglobulin heavy alpha, gamma, and delta chains, and CH4 domain (fourth constant Ig domain of the heavy chain) in immunoglobulin heavy alpha, epsilon, and mu chains; member of the C1-set of I; The members here are composed of the third and fourth immunoglobulin constant domain (IgC) of alpha, delta, gamma and alpha, epsilon, and mu heavy chains, respectively. This domain is found on the Fc fragment. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. There are two types of light chains: kappa and lambda; each is composed of a constant domain and a variable domain. There are five types of heavy chains: alpha, delta, epsilon, gamma, and mu, all consisting of a variable domain (VH) with three (alpha, delta and gamma) or four (epsilon and mu) constant domains (CH1 to CH4). Ig molecules are modular proteins, in which the variable and constant domains have clear, conserved sequence patterns.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 129 PTVTISPSRTEALNHHNL--LVCSVTDFYPGQIKVRWFRNDQE-ETAGVVSTPLIRNGDWTFQILVMLEMTPQ---RGDV 202
Cdd:cd05768    1 PSVYLLPPPEEELSLNETvtLTCLVKGFYPEDIFVSWLQNGEPlPSADYKTTAPVPESDGSFFVYSKLNVSTAdwnSGDV 80

                         90
                 ....*....|....*.
gi 345461081 203 YTCHVEHPSLQSPITV 218
Cdd:cd05768   81 FSCVVGHEALPLQFTQ 96

T cell receptor (TCR) beta chain constant immunoglobulin domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the T cell receptor (TCR) beta chain constant immunoglobulin domain. TCRs mediate antigen recognition by T lymphocytes, and are composed of alpha and beta, or gamma and delta, polypeptide chains with variable (V) and constant (C) regions. This group includes the variable domain of the beta chain. Alpha/beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. The antigen binding site is formed by the variable domains of the alpha and beta chains, located at the N-terminus of each chain. Alpha/beta TCRs recognize antigens differently from gamma/delta TCRs.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 128 EPTVTI-SPSRTEALNHHNL-LVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPL-IRNGDWTFQILVMLEMTPQR----G 200
Cdd:cd05769    2 PPTVALfPPSEAEIRNKRKAtLVCLATGFYPDHVSLSWKVNGKEVKDGVATDPQaLRENTSTYSLSSRLRVSATEwfnpR 81

                 ....*....
gi 345461081 201 DVYTCHVEH 209
Cdd:cd05769   82 NTFTCIVKF 90

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) F; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen alpha chain F (HLA-F). HLA-F, encoded by the HLA-F gene in humans, belongs to the non-classical HLA class I heavy chain paralogs. This class I molecule mainly exists as a heterodimer associated with the invariant light chain beta-2-microglobulin. HLA-F molecules can interact with both activating and inhibitory receptors on immune cells, such as NK cells, and can present a diverse panel of peptides. Class I MHC proteins bind antigenic peptide fragments and present them to CD8+ T lymphocytes. Class I molecules consist of a transmembrane alpha chain and a small chain called the beta-2-microglobulin. The alpha chain contains three extracellular domains, two of which fold together to form the peptide-binding cleft (alpha1 and alpha2), and one which has an Ig fold (alpha3). Peptide binding to class I molecules occurs in the endoplasmic reticulum (ER) and involves both chaperones and dedicated factors to assist in peptide loading. Class I MHC molecules are expressed on most nucleated cells.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 345461081 142 NHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTCHVEHPSLQSPITVEW 220
Cdd:cd21023   17 DHEATLRCWALGFYPAEITLTWQRDGEEQTQDTELVETRPAGDGTFQKWAAVVVPPGEEQRYTCHVQHEGLPQPLILRW 95

CH2 domain (second constant Ig domain of the heavy chain) in immunoglobulin E (IgE); member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the second constant domain of the heavy chain of immunoglobulin E (IgE). The basic structure of immunoglobulin (Ig) molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. There are two types of light chains: kappa and lambda; each is composed of a constant domain and a variable domain. There are five types of heavy chains: alpha, delta, epsilon, gamma, and mu, all consisting of a variable domain (VH) with three (alpha, delta, and gamma) or four (epsilon and mu) constant domains (CH1 to CH4). The different classes of antibodies vary in their heavy chains; the IgE class has the epsilon type. This domain (Cepsilon2) of IgE is in place of the flexible hinge region found in IgG.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 129 PTVTISPSRTEALNHHNL--LVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQR---GDVY 203
Cdd:cd05847    1 PTVQILHSSCASTLTSETiqLLCLISGYTPSTIEVEWLVDGQVATLSAASTAPQKEEGGTFSTTSKLNVTQEDwksGKTY 80

                 ....*..
gi 345461081 204 TCHVEHP 210
Cdd:cd05847   81 TCKVTHQ 87

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) E; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) E. HLA-E is the first human class Ib major histocompatibility complex molecule to be crystallized. Like other MHC class I molecules, HLA-E is a heterodimer consisting of an a heavy chain and light chain beta-2-microglobulin. HLA-E is highly conserved and almost nonpolymorphic, and has recently been shown to be the first specialized ligand for natural killer cell receptors. Class I MHC proteins bind antigenic peptide fragments and present them to CD8+ T lymphocytes. Class I molecules consist of a transmembrane alpha chain and a small chain called the beta-2-microglobulin. The alpha chain contains three extracellular domains, two of which fold together to form the peptide-binding cleft (alpha1 and alpha2), and one which has an Ig fold (alpha3). Peptide binding to class I molecules occurs in the endoplasmic reticulum (ER) and involves both chaperones and dedicated factors to assist in peptide loading. Class I MHC molecules are expressed on most nucleated cells.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 345461081 142 NHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTCHVEHPSLQSPITVEW 220
Cdd:cd21024   17 DHEATLRCWALGFYPAEITLTWQQDGEGHTQDTELVETRPAGDGTFQKWAAVVVPSGEEQRYTCHVQHEGLPEPVTLRW 95

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of HLA-Cw3 and HLA-Cw4; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class Ib major histocompatibility complex (MHC) immunoglobulin domain of HLA-Cw3 and HLA-Cw4. HLA-C belongs to the MHC class I heavy chain receptors. The C receptor is a heterodimer consisting of a HLA-C mature gene product and beta-2-microglobulin. The mature C chain is anchored in the membrane. MHC Class I molecules, like HLA-C, are expressed in nearly all cells, and present small peptides to the immune system which surveys for non-self peptides. HLA-C is a locus on chromosome 6, which encodes for a large number of HLA-C alleles that are Class-I MHC receptors. Class Ib histocompatibility leukocyte antigens (HLA)-Cw3 and (HLA)-Cw4 are ligands for the natural killer (NK) cell inhibitory receptors KIR2DL2 and KIR2DL1, respectively. HLA-Cw3 and related alleles (HLA-Cw1, -Cw7, and -Cw8) contain Ser77 and Asn80 and interact with KIR that are reactive with the GL183 antibody Class I MHC proteins bind antigenic peptide fragments and present them to CD8+ T lymphocytes. HLA-Cw4 and related alleles (HLA-Cw2, -Cw5, and -Cw6) have Asn77 and Lys80 and are recognized by KIR reactive with the EB6 15 or HP-3E4 16 antibody. Members of the IgC family are components of immunoglobulin, T-cell receptors, CD1 cell surface glycoproteins, secretory glycoproteins A/C, and major histocompatibility complex (MHC) class I/II molecules. In immunoglobulins, each chain is composed of one variable domain (IgV) and one or more IgC domains. These names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. The IgV domain is responsible for antigen binding, and the IgC domain is involved in oligomerization and molecular interactions.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 142 NHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTCHVEHPSLQSPITVEWR 221
Cdd:cd21025   17 DHEATLRCWALGFYPAEITLTWQWDGEDQTQDTELVETRPAGDGTFQKWAAVVVPSGEEQRYTCHVQHEGLPEPLTLRWE 96

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) G; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) G. HLA-G histocompatibility antigen (also known as human leukocyte antigen G ; HLA-G) is a protein that in humans is encoded by the HLA-G gene. HLA-G belongs to the HLA nonclassical class I heavy chain paralogs. This class I molecule is a heterodimer consisting of a heavy chain and light chain, beta-2-microglobulin. The heavy chain is anchored in the membrane. HLA-G may play a role in immune tolerance in pregnancy, being expressed in the placenta by extravillous trophoblast cells (EVT), while the classical MHC class I genes (HLA-A and HLA-B) are not. Immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class I and class II. Class I MHC proteins bind antigenic peptide fragments and present them to CD8+ T lymphocytes. Class I molecules consist of a transmembrane alpha chain and a small chain called the beta-2-microglobulin. The alpha chain contains three extracellular domains, two of which fold together to form the peptide-binding cleft (alpha1 and alpha2), and one which has an Ig fold (alpha3). Peptide binding to class I molecules occurs in the endoplasmic reticulum (ER) and involves both chaperones and dedicated factors to assist in peptide loading. Class I MHC molecules are expressed on most nucleated cells. MHC class II molecules play a key role in the initiation of the antigen-specific immune repose. These molecules have been shown to be expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice. The expression of these molecules has been shown to be induced in nonprofessional APCs such as keratinocyctes, and they are expressed on the surface of activated human T cells and on T cells from other species. The MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes. These peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC. These peptides bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 134 SPSRTEALNH-----HNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTCHVE 208
Cdd:cd21022    3 DPPKTHVTHHpvfdyEATLRCWALGFYPAEIILTWQRDGEDQTQDVELVETRPAGDGTFQKWAAVVVPSGEEQRYTCHVQ 82

                         90
                 ....*....|..
gi 345461081 209 HPSLQSPITVEW 220
Cdd:cd21022   83 HEGLPEPLMLRW 94

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of Qa-1b; member of the C1-set of Ig superfamily (IgSF) domains; The non-classical mouse MHC class I (MHC-I) molecule Qa-1b is a non-polymorphic MHC molecule with an important function in innate immunity. It binds and presents signal peptides of classical MHC-I molecules at the cell surface and, as such, act as an indirect sensor for the normal expression of MHC-I molecules. This signal peptide dominantly accommodated in the groove of Qa-1b is called Qdm, for Qa-1 determinant modifier, and its amino acid sequence AMAPRTLLL is highly conserved among mammalian species. The Qdm/Qa-1b complex serves as a ligand for the germ-line encoded heterodimeric CD94/NKG2A receptors expressed on natural killer (NK) cells and activated CD8+ T cells and transduces inhibitory signals to these lymphocytes. Thus, upon binding, Qa-1b signals NK cells not to engage in cell lysis. The molecular basis of Qa-1b function is unclear.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....
gi 345461081 147 LVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTCHVEHPSLQSPITVEW 220
Cdd:cd21820   22 LRCWALGFYPADITLTWQLNGEELTQDMELVETRPAGDGTFQKWAAVVVPLGKEQYYTCHVYHEGLPEPLTLRW 95

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of T10, T22, and similar proteins; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class Ib major histocompatibility complex (MHC) immunoglobulin domain of the murine H-2T-encoded T10, T22, and similar proteins. T10 and T22 are highly related nonclassical major histocompatibility complex (MHC) class Ib proteins that bind to certain gammadelta T cell receptors (TCRs) in the absence of other components. Classical MHC class I (class Ia) molecules participate in immune responses by presenting peptide antigens to cytolytic alpha beta T cells. Many nonclassical MHC class I (class Ib) molecules have distinct antigen-binding capabilities, suggesting that they have evolved for specific tasks that are distinct from those of MHC class Ia. Members of the IgC family are components of immunoglobulin, T-cell receptors, CD1 cell surface glycoproteins, secretory glycoproteins A/C, and major histocompatibility complex (MHC) class I/II molecules. In immunoglobulins, each chain is composed of one variable domain (IgV) and one or more IgC domains. These names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. The IgV domain is responsible for antigen binding, and the IgC domain is involved in oligomerization and molecular interactions.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....
gi 345461081 147 LVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTCHVEHPSLQSPITVEW 220
Cdd:cd21016   22 LRCWALGFYPADITLTWQKDGEELTQDMEFVETRPAGDGTFQKWAAVVVPLGKEQSYTCHVYHEGLPEPLTLRW 95

H-2 class I histocompatibility complex TLA (thymus leukemia antigen); member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the major histocompatibility complex (MHC) H-2 class I histocompatibility complex TLA (thymus leukemia antigen). The murine MHC class I histocompatibility TLA (Thymus leukemia antigen), which is encoded in the T region by T3 and T18 genes, is expressed mainly by intestinal epithelial cells and thymocytes. The murine TLAs are class I, beta-2-microglobulin-associated glycoproteins. The TLA function is not defined by antigen presentation, but rather by its relatively high affinity binding to CD8-alpha-alpha compared with CD8-alpha-beta. The existence of a human homolog for murine TLA remains unresolved. This group is a member of the C1-set Ig domains, which have one beta sheet that is formed by strands A, B, E, and D and the other strands by G, F, C, and C'.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 135 PSRTEALNH-----HNLLVCSVTDFYPGQIKVRWFRNDQE---ETAGVVSTPLirnGDWTFQILVMLEMTPQRGDVYTCH 206
Cdd:cd21012    5 PPKTHVTHHprpegYVTLRCWALGFYPAHITLTWQLNGEEliqDTELVETRPA---GDGTFQKWAAVVVPSGEEQKYTCH 81

                         90
                 ....*....|....
gi 345461081 207 VEHPSLQSPITVEW 220
Cdd:cd21012   82 VYHEGLPEPLTLRW 95

Signal-regulatory protein (SIRP) immunoglobulin-like domain 2; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig)-like domain in Signal-Regulatory Protein (SIRP), domain 2 (C1 repeat 1). The SIRPs belong to the "paired receptors" class of membrane proteins that comprise several genes coding for proteins with similar extracellular regions, but very different transmembrane/cytoplasmic regions with different (activating or inhibitory) signaling potentials. They are commonly on NK cells, but are also on many myeloid cells. Their extracellular region contains three Immunoglobulin superfamily domains, a single V-set and two C1-set IgSF domains. Their cytoplasmic tails contain either ITIMs or transmembrane regions that have positively charged residues that allow an association with adaptor proteins, such as DAP12/KARAP, containing ITAMs. There are 3 distinct SIRP members: alpha, beta, and gamma. SIRP alpha (also known as CD172a or SRC homology 2 domain-containing protein tyrosine phosphatase substrate 1/Shps-1) is a membrane receptor that interacts with a ligand CD47 expressed on many cells and gives an inhibitory signal through immunoreceptor tyrosine-based inhibition motifs in the cytoplasmic region that interact with phosphatases SHP-1 and SHP-2. SIRP beta has a short cytoplasmic region and associates with a transmembrane adapter protein DAP12 containing immunoreceptor tyrosine-based activation motifs to give an activating signal. SIRP gamma contains a very short cytoplasmic region lacking obvious signaling motifs, but also binds CD47, but with much less affinity.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 129 PTVTISPSRTEAlNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVS-TPLirNGDWTFQILVMLEMTPQRGDVY---T 204
Cdd:cd05772    5 PLVSGPSGRATP-GQTVSFTCKSHGFSPRDITLKWFKNGNELSALQTTvFPE--GDSVSYSVSSTVQVVLTKDDVHsqlT 81

                         90
                 ....*....|...
gi 345461081 205 CHVEHPSLQSPIT 217
Cdd:cd05772   82 CEVAHVTLQAPLR 94

Class Ia major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) H2Db and H2Ld; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class Ia major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) H2Db and H2Ld. H-2Ld complexed with peptide QL9 (or p2Ca) and complexed with influenza virus peptide NP366-374 (ASNEN-METM), respectively are high-affinity alloantigens for the 2C T cell receptor (TCR). The a1-a2 super domains of H-2Ld, H-2Db, and H-2Kb closely superimpose. Class I MHC proteins bind antigenic peptide fragments and present them to CD8+ T lymphocytes. Class I molecules consist of a transmembrane alpha chain and a small chain called the beta-2-microglobulin. The alpha chain contains three extracellular domains, two of which fold together to form the peptide-binding cleft (alpha1 and alpha2), and one which has an Ig fold (alpha3). Peptide binding to class I molecules occurs in the endoplasmic reticulum (ER) and involves both chaperones and dedicated factors to assist in peptide loading. Class I MHC molecules are expressed on most nucleated cells.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....
gi 345461081 147 LVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTCHVEHPSLQSPITVEW 220
Cdd:cd21018   22 LRCWALGFYPADITLTWQLNGEELTQDMELVETRPAGDGTFQKWASVVVPLGKEQNYTCRVYHEGLPEPLTLRW 95

Class II major histocompatibility complex (MHC) alpha chain immunoglobulin domain of histocompatibility antigen (HLA) DM; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class II alpha chain of histocompatibility antigen (HLA) DM. Human HLA-DM, also known as H2-M in mice, plays a critical role in antigen presentation to CD4 T cells by catalyzing the exchange of peptides bound to MHC class II molecules. MHC class II molecules play a key role in the initiation of the antigen-specific immune reponse. These molecules have been shown to be expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice. The expression of these molecules has been shown to be induced in nonprofessional APCs such as keratinocyctes, and they are expressed on the surface of activated human T cells and on T cells from other species. The MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes. These peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC. These peptides bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 345461081 145 NLLVCSVTDFYPGQIKVRWfRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTCHVEH 209
Cdd:cd21009   19 NTLVCFVSNLFPPMLTVNW-QLHSVPVEGFGPTFVSAVDGLSFQAFSYLNFTPEPSDIFSCIVTH 82

CH1 domain (first constant Ig domain of the heavy chain) in immunoglobulin heavy epsilon and gamma chain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the first immunoglobulin constant-1 set domain of epsilon and gamma chains. It belongs to a family composed of the first immunoglobulin constant-1 set domain of alpha, delta, epsilon, gamma, and mu heavy chains. This domain is found on the Fab antigen-binding fragment. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. There are two types of light chains: kappa and lambda; each is composed of a constant domain and a variable domain. There are five types of heavy chains: alpha, delta, epsilon, gamma, and mu, all consisting of a variable domain (VH) with three (alpha, delta and gamma) or four (epsilon and mu) constant domains (CH1 to CH4). Ig molecules are modular proteins, in which the variable and constant domains have clear, conserved sequence patterns. This group belongs to the C1-set of IgSF domains, which are classical Ig-like domains resembling the antibody constant domain. C1-set domains are found almost exclusively in molecules involved in the immune system, such as in immunoglobulin light and heavy chains, in the major histocompatibility complex (MHC) class I and II complex molecules, and in various T-cell receptors.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 129 PTV-TISPSRTEALNHHNLLVCSVTDFYPGQIKVRWfrNDQEETAGVVSTPLIR--NGDWTFQILVMLEMTPQRGDVYTC 205
Cdd:cd21817    2 PSVfPLAPCCKSTNGSSVTLGCLVTGYFPEPVTVTW--NSGSLTSGVKTFPAVLqsSGLYTTSSQVTVPSSSWGSQTFTC 79

                         90
                 ....*....|....*
gi 345461081 206 HVEHPslqsPITVEW 220
Cdd:cd21817   80 NVEHK----PSSTKV 90

T cell receptor (TCR) gamma chain constant immunoglobulin domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) constant (C) domain of the gamma chain of gamma-delta T-cell receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes and are heterodimers consisting of alpha and beta chains or gamma and delta chains. Each chain contains a variable (V) and a constant (C) region. The majority of T cells contain alpha-beta TCRs, but a small subset contain gamma-delta TCRs. Alpha-beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. Gamma-delta TCRs recognize intact protein antigens; they recognize protein antigens directly and without antigen processing and MHC independently of the bound peptide. Gamma-delta T cells can also be stimulated by non-peptide antigens such as small phosphate- or amine-containing compounds.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 345461081 128 EPTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGD--WTFQILVMLEMTPqrGDVYTC 205
Cdd:cd07697    3 KPTIFLPSIAETEKQKAGTYLCLLENFFPDVIKIHWREKKSDTILESQEGNTEKTKDtyMKFSWLTVPKKSL--GKEHRC 80

                 ....
gi 345461081 206 HVEH 209
Cdd:cd07697   81 IYKH 84