Immunoglobulin domain; The members here are composed of the immunoglobulin (Ig) domain found in the Ig superfamily. The Ig superfamily is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. Members of this group are components of immunoglobulin, neuroglia, cell surface glycoproteins, including T-cell receptors, CD2, CD4, CD8, and membrane glycoproteins, including butyrophilin and chondroitin sulfate proteoglycan core protein. A predominant feature of most Ig domains is a disulfide bridge connecting the two beta-sheets with a tryptophan residue packed against the disulfide bond. Ig superfamily (IgSF) domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. Typically, the V-set domains have A, B, E, and D strands in one sheet and A', G, F, C, C' and C" in the other. 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 by strands G, F, C, and C'. Moreover, a C1-set Ig domain contains a short C' strand (three residues) and lacks A' and C" strand. Unlike other Ig domain sets, C2-set structures do not have a D strand. Like the V-set Ig domains, members of the I-set have a discontinuous A strand, but lack a C" strand.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 2322547333 138 PPTVTIFDPSAQELQEKQKVTIVCLVTDFYPDHVNLTWSVDGDERTKGVKTKEPDLDKAAKKFSLISRLRITRKEWEKTK 217
Cdd:cd05769     2 PPTVALFPPSEAEIRNKRKATLVCLATGFYPDHVSLSWKVNGKEVKDGVATDPQALRENTSTYSLSSRLRVSATEWFNPR 81

                          90
                  ....*....|..
gi 2322547333 218 E-IQCNVYFDPL 228
Cdd:cd05769    82 NtFTCIVKFYGG 93

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 2322547333 138 PPTVTIFDPSAQELQEKQKVTIVCLVTDFYPDHVNLTWSVDGDERTKGVKTKEPDLDKAAKKFSLISRLRITRKEWEKTK 217
Cdd:cd05769     2 PPTVALFPPSEAEIRNKRKATLVCLATGFYPDHVSLSWKVNGKEVKDGVATDPQALRENTSTYSLSSRLRVSATEWFNPR 81

                          90
                  ....*....|..
gi 2322547333 218 E-IQCNVYFDPL 228
Cdd:cd05769    82 NtFTCIVKFYGG 93

Immunoglobulin V-set domain; This domain is found in antibodies as well as neural protein P0 and CTL4 amongst others.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 2322547333  30 EGQNAHLKCT----QNNGHNEMYWYRQKGGKELQ-LLFYFNNKvlINKGNITDRFT-SDQPELDHSSLKISPAQPEDSAV 103
Cdd:pfam07686  10 LGGSVTLPCTysssMSEASTSVYWYRQPPGKGPTfLIAYYSNG--SEEGVKKGRFSgRGDPSNGDGSLTIQNLTLSDSGT 87

                          90       100
                  ....*....|....*....|....*..
gi 2322547333 104 YFCASSYRgastaETLYFGQGTRLTVV 130
Cdd:pfam07686  88 YTCAVIPS-----GEGVFGKGTRLTVL 109

Immunoglobulin like; IG domains that cannot be classified into one of IGv1, IGc1, IGc2, IG.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 2322547333   29 MEGQNAHLKCT-QNNGHNEMYWYRQKGgkelqllfyfnnKVLINKGNITDRFTSDQpeldhSSLKISPAQPEDSAVYFCA 107
Cdd:smart00410   7 KEGESVTLSCEaSGSPPPEVTWYKQGG------------KLLAESGRFSVSRSGST-----STLTISNVTPEDSGTYTCA 69

                           90       100
                   ....*....|....*....|..
gi 2322547333  108 ssyrgASTAETLYFGqGTRLTV 129
Cdd:smart00410  70 -----ATNSSGSASS-GTTLTV 85

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 2322547333 138 PPTVTIFDPSAQELQEKQKVTIVCLVTDFYPDHVNLTWSVDGDERTKGVKTKEPDLDKAAKKFSLISRLRITRKEWEKTK 217
Cdd:cd05769     2 PPTVALFPPSEAEIRNKRKATLVCLATGFYPDHVSLSWKVNGKEVKDGVATDPQALRENTSTYSLSSRLRVSATEWFNPR 81

                          90
                  ....*....|..
gi 2322547333 218 E-IQCNVYFDPL 228
Cdd:cd05769    82 NtFTCIVKFYGG 93

Immunoglobulin (Ig) variable (V) domain of T-cell receptor (TCR) alpha chain and similar proteins; The members here are composed of the immunoglobulin (Ig) variable domain of the alpha chain of alpha/beta T-cell antigen receptors (TCRs). 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 represents the variable domain of the alpha chain of TCRs and also includes the variable domain of delta chains of TCRs. Alpha/beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. The variable domain of TCRs is responsible for antigen recognition, and is located at the N-terminus of the receptor. Gamma/delta TCRs recognize intact protein antigens directly without antigen processing and recognize MHC independently of the bound peptide. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 2322547333  26 LALMEGQNAHLKCT-QNNGHNEMYWYRQKGGKELQLLFYFNNKVLiNKGNitDRFTSD-QPELDHSSLKISPAQPEDSAV 103
Cdd:cd04983     8 LSVQEGENVTLNCNySTSTFYYLFWYRQYPGQGPQFLIYISSDSG-NKKK--GRFSATlDKSRKSSSLHISAAQLSDSAV 84

                          90       100
                  ....*....|....*....|....*.
gi 2322547333 104 YFCASSyrGASTAETLYFGQGTRLTV 129
Cdd:cd04983    85 YFCALS--ESGGTGKLTFGKGTRLTV 108

Immunoglobulin C1-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 2322547333 141 VTIFDPSAQELqeKQKVTIVCLVTDFYPDHVNLTWSVDGDERTKGVKTKEPDLDKAAkKFSLISRLRITRKEWEKTKEIQ 220
Cdd:pfam07654   1 VYVFPPSPEEL--GKPNTLTCLVTGFYPPDITVTWLKNGQEVTEGVKTTPPSPNSDW-TYQLSSYLTVTPSDWESGDEYT 77

                  ...
gi 2322547333 221 CNV 223
Cdd:pfam07654  78 CRV 80

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 2322547333 140 TVTIFDPSAQELqEKQKVTIVCLVTDFYPDHVNLTWSVDGDERTKGVKTKEPdLDKAAKKFSLISRLRITRKEWEKTKEI 219
Cdd:cd00098     1 TVTLLPPSPEEK-GGGKVTLVCLVSGFYPKDITVTWLKNGVPLTSGVSTSSP-VEPNDGTYSVTSSLTVPPSDWDEGATY 78

                          90
                  ....*....|..
gi 2322547333 220 QCNVYFDPLKQN 231
Cdd:cd00098    79 TCVVTHESLKSP 90

Immunoglobulin (Ig) lambda light chain variable (V) domain; The members here are composed of the immunoglobulin (Ig) light chain, lambda type, variable (V) domain. 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 composed of a constant domain (CL) and a variable domain (VL). There are five types of heavy chains (alpha, gamma, delta, epsilon, and mu), which determines the type of immunoglobulin formed: 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. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 2322547333  31 GQNAHLKCTQNNGH---NEMYWYRQKGGKELQLLFYFNNKvliNKGNITDRFtSDQPELDHSSLKISPAQPEDSAVYFCA 107
Cdd:cd04984    13 GETVTITCTGSSGNisgNYVNWYQQKPGSAPRYLIYEDKH---RPSGIPDRF-SGSKSGNTASLTISGAQTEDEADYYCQ 88

                          90       100
                  ....*....|....*....|..
gi 2322547333 108 SSYrgastAETLYFGQGTRLTV 129
Cdd:cd04984    89 VWD-----SNSYVFGGGTKLTV 105

Immunoglobulin C-Type;

                           10        20        30        40        50        60
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 2322547333  156 KVTIVCLVTDFYPDHVNLTWSVDGDERTKGVKTKEPDLDKAAkKFSLISRLRITRKEWEKTKEIQCNV 223
Cdd:smart00407   1 KATLVCLVSGFYPPDITVTWLRNGQEVTEGVSTTDPLKNSDG-TYFLSSYLTVPASTWESGDVYTCQV 67

Immunoglobulin (Ig) variable (V) domain of T-cell receptor (TCR) delta chain; The members here are composed of the immunoglobulin (Ig) variable (V) domain of the delta 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. The variable domain of gamma/delta TCRs is responsible for antigen recognition and is located at the N-terminus of the receptor. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 2322547333  30 EGQNAHLKCTQNNGHNEMY--WYRQKGGKELQLLFYFNNKVLiNKGNitDRFTSDQPELDHS-SLKISPAQPEDSAVYFC 106
Cdd:cd07706    13 VGEEVTLNCRYETSWTNYYlfWYKQLPSGEMTFLIRQDSSEQ-NAKS--GRYSVNFQKAQKSiSLTISALQLEDSAKYFC 89

                          90       100
                  ....*....|....*....|...
gi 2322547333 107 ASSYRGAStaETLYFGQGTRLTV 129
Cdd:cd07706    90 ALSLPYDT--DKLIFGKGTRLTV 110

Immunoglobulin (Ig) heavy chain (H), variable (V) domain; The members here are composed of the immunoglobulin (Ig) heavy chain (H), variable (V) domain. This group contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology. 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 determines the type of immunoglobulin formed: IgA, IgG, IgD, IgE, and IgM, respectively. In higher vertebrates, there are two types of light chain, designated kappa and lambda, which can associate with any of the heavy chains. This family includes alpha, gamma, delta, epsilon, and mu heavy chains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 2322547333  47 MYWYRQKGGKELQLL-FYFNNKVLIN-----KGNITdrFTSDQpeldhSS----LKISPAQPEDSAVYFCASSYRGASTA 116
Cdd:cd04981    32 MGWVRQAPGKGLEWIgLIYPGGGDTYyadsfKGRFT--ITRDT-----SKstayLQLNSLTSEDTAVYYCARGLGGYGYS 104

                          90
                  ....*....|...
gi 2322547333 117 ETLYFGQGTRLTV 129
Cdd:cd04981   105 YFDYWGQGTTVTV 117

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 2322547333 139 PTVTIFDPSAQELQEKQKVTIVCLVTDFYPDHVNLTWSVDGDERTKGVKTKEPDLDkAAKKFSLISRLRITRKEWEKTKE 218
Cdd:cd05847     1 PTVQILHSSCASTLTSETIQLLCLISGYTPSTIEVEWLVDGQVATLSAASTAPQKE-EGGTFSTTSKLNVTQEDWKSGKT 79

                  ....*
gi 2322547333 219 IQCNV 223
Cdd:cd05847    80 YTCKV 84

CH1 domain (first constant Ig domain of the heavy chain) in immunoglobulin heavy mu 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 mu 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
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 2322547333 157 VTIVCLVTDFYPDHVNLTWSVDGDERTKGVKTKEPDLDKAakKFSLISRLRITRKEWEKTKEIQCNV 223
Cdd:cd21819    18 VTVGCLATDFLPDSITFSWTDDNNSLTTGVKTYPSVLTGG--TYTASSQLQVPESEWKSKENFYCKV 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 2322547333 138 PPTVTIFDPSAQELQEKQkVTIVCLVTDFYPDHVNLTWsvDGDERTKGVKTKePDLDKAAKKFSLISRLRITRKEWEkTK 217
Cdd:cd21817     1 APSVFPLAPCCKSTNGSS-VTLGCLVTGYFPEPVTVTW--NSGSLTSGVKTF-PAVLQSSGLYTTSSQVTVPSSSWG-SQ 75

                          90
                  ....*....|....*....
gi 2322547333 218 EIQCNVYFDPLKQNYTGTI 236
Cdd:cd21817    76 TFTCNVEHKPSSTKVDKKI 94

Immunoglobulin domain of Cluster of Differentiation (CD) 1; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin domain of Cluster of Differentiation (CD) 1. CD1 family of transmembrane glycoproteins, are structurally related to the major histocompatibility complex (MHC) proteins and form heterodimers with beta-2-microglobulin. They mediate the presentation of primarily lipid and glycolipid antigens of self or microbial origin to T cells. The human genome contains five CD1 family genes (CD1a, CD1b, CD1c, CD1d, and CD1e) organized in a cluster on chromosome 1. The CD1 family members are thought to differ in their cellular localization and specificity for particular lipid ligands. CD1a localizes to the plasma membrane and to recycling vesicles of the early endocytic system. Alternative splicing results in multiple transcript variants. 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. C1-set Ig domains 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
                  ....*....|....*....|....*....|....*....|....*....|....
gi 2322547333 137 SPPTVTIFDPSAQElqeKQKVTIVCLVTDFYPDHVNLTWSVDGDERTKGVKTKE 190
Cdd:cd21029     1 VKPRVRLSSRPSPG---DGHLQLSCHVTGFYPRPIEVTWLRDGQEQMDGTQSGG 51

CH3 domain (third constant Ig domain of heavy chains) in immunoglobulin heavy alpha, epsilon, and mu chains, and CH2 domain (second constant Ig domain of the gheavy chain) in immunoglobulin heavy gamma chain; member of the C1-set of Ig superfamily (IgSF) ; The members here are composed of the third immunoglobulin constant domain (IgC) of the gamma heavy chains and the second immunoglobulin constant domain (IgC) of alpha, epsilon, and mu heavy chains. 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 2322547333 139 PTVTIFDPSAQELQEKQKVTIVCLVTDFYP-DHVNLTWSVDGDERTKGVKTKEPDLDKAAkkFSLISRLRITRKEWEKTK 217
Cdd:cd07696     1 VSVFLIPPSPKDLFLTKSAKVTCLVVDLTSiEEVNVTWSREDGNEVLASTTNPEKHYNAT--LSVVSTLTVCADDWDNGK 78

                  ....*.
gi 2322547333 218 EIQCNV 223
Cdd:cd07696    79 TFKCKV 84

CH1 domain (first constant Ig domain of the heavy chain) in immunoglobulin heavy alpha 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 alpha chains. It belongs to a family composed of the first immunoglobulin constant-1 set domain of alpha, 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 2322547333 142 TIFDPSAQELQEKQKVTIVCLVTDFYPDHVNLTWSVDGDERTkgVKTKEPDLDkAAKKFSLISRLRITRKEWEKTKEIQC 221
Cdd:cd21818     3 TVFPLSLCPSLSSDPVVIGCLVQGFFPEPVNVTWNYSGKGGT--ARNFPAMLA-SGGRYTQSSQLTLPADQCPEGEAYKC 79

                          90
                  ....*....|..
gi 2322547333 222 NVYFDPLKQNYT 233
Cdd:cd21818    80 SVQHYSPSQDLN 91

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DR; 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) DR. HLA-DR is an MHC class II cell surface receptor encoded by the human leukocyte antigen complex on chromosome 6 region 6p21.31. HLA-DR is also involved in several autoimmune conditions, disease susceptibility, and disease resistance including seronegative-rheumatoid arthritis, penicillamine-induced myasthenia, schizophrenia, Goodpasture syndrome, systemic lupus erythematosus, Alzheimers, tuberculoid leprosy, and Hashimoto's thyroiditis. HLA-DR molecules are upregulated in response to signaling. HLA-DR is an alphabeta heterodimer cell surface receptor, each subunit of which contains two extracellular domains, a membrane-spanning domain, and a cytoplasmic tail. Both alpha and beta chains are anchored in the membrane. The DR beta chain is encoded by 4 loci, however no more than 3 functional loci are present in a single individual, and no more than two on a single chromosome. Sometimes an individual may only possess 2 copies of the same locus, DRB1*. The HLA-DRB1 locus is ubiquitous and encodes a very large number of functionally variable gene products (HLA-DR1 to HLA-DR17). The HLA-DRB3 locus encodes the HLA-DR52 specificity, is moderately variable and is variably associated with certain HLA-DRB1 types. The HLA-DRB4 locus encodes the HLA-DR53 specificity, has some variation, and is associated with certain HLA-DRB1 types. The HLA-DRB5 locus encodes the HLA-DR51 specificity, which is typically invariable, and is linked to the HLA-DR2 types. 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). 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
                  ....*....|....*....|....*....|....*....|....*...
gi 2322547333 139 PTVTIFDPSAQELQEKQkvTIVCLVTDFYPDHVNLTWSVDGDERTKGV 186
Cdd:cd21000     4 PKVTVYPAKTQPLQHHN--LLVCSVNGFYPGSIEVRWFRNGQEEKAGV 49

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
                  ....*....|....*....|....*....|...
gi 2322547333 159 IVCLVTDFYPDHVNLTWSVDGDERTKGVKTKEP 191
Cdd:cd21003    22 LVCHVTDFYPGNIQVRWFLNGQEETAGVVSTNL 54

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
                  ....*....|....*....|....*....|....*....|....*...
gi 2322547333 139 PTVTIFDPSAQELQEKQkvTIVCLVTDFYPDHVNLTWSVDGDERTKGV 186
Cdd:cd20998     7 PTVTVYPTKTQPLEHHN--LLVCSVSDFYPGNIEVRWFRNGKEEKTGI 52

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
                  ....*....|....*....|....*....|....*....|....*....|....
gi 2322547333 138 PPTVTIFDPSAQElqekQKVTIVCLVTDFYPDHVNLTWSVDGDERTKGVKTKEP 191
Cdd:cd07698     2 PPKVHVTHHPRSD----GESTLRCWALGFYPAEITLTWQRDGEDQTQDMELVET 51

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 2322547333  27 ALMEGQNAHLKCT-QNNGHNEMYWYRQkggkelqllfyfnnkvliNKGNITDRFTSDQPELDHSSLKISPAQPEDSAVYF 105
Cdd:pfam13927  12 TVREGETVTLTCEaTGSPPPTITWYKN------------------GEPISSGSTRSRSLSGSNSTLTISNVTRSDAGTYT 73

                  .
gi 2322547333 106 C 106
Cdd:pfam13927  74 C 74

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        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 2322547333 152 QEKQKVTIVCLVTDFYPDHVNLTWSVDGDERTKGVKTKE--PDLDKAAKKF-SLISRLritrkewEKTKEIQCNVYFDPL 228
Cdd:cd21018    15 RSKGEVTLRCWALGFYPADITLTWQLNGEELTQDMELVEtrPAGDGTFQKWaSVVVPL-------GKEQNYTCRVYHEGL 87

                  ....*
gi 2322547333 229 KQNYT 233
Cdd:cd21018    88 PEPLT 92