Fifth domain (immunoglobulin-like) of Trk receptor TrkB; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the fifth domain of Trk receptor, TrkB, an immunoglobulin (Ig)-like domain which binds to neurotrophin. The Trk family of receptors are tyrosine kinase receptors, which mediate the trophic effects of the neurotrophin Nerve Growth Factor (NGF) family. Trks are activated by dimerization, leading to autophosphorylation of intracellular tyrosine residues, and triggering the signal transduction pathway. TrkB shares significant sequence homology and domain organization with TrkA and TrkC. The first three domains are leucine-rich domains while the fourth and fifth domains are Ig-like domains playing a part in ligand binding. TrKB is recognized by brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-4. In some cell systems NT-3 can activate TrkA and TrkB receptors. TrKB transcripts are found throughout multiple structures of the central and peripheral nervous systems. This group belongs to the I-set of IgSF domains

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842 130 APTITFLESPTSDHHWCIPFTVKGNPKPALQWFYNGAILNESKYICTKIHVTNHTEYHGCLQLDNPTHMNNGDYTLIAKN 209
Cdd:cd05855     1 PPTITFLELPTRDHHWCIPFTVKGNPKPTLQWFHEGAILNESEYICTKIHVINNTEYHGCLQLDNPTHLNNGIYTLVAKN 80

                          90
                  ....*....|....
gi 1610576842 210 EYGKDEKQISAHFM 223
Cdd:cd05855    81 EYGEDEKNVSAHFM 94

Leucine rich repeat C-terminal motif; This entry represents the Leucine Rich Repeat C-terminal (LRRCT) capping motif from TRK receptors.

                          10        20        30        40
                  ....*....|....*....|....*....|....*....|
gi 1610576842   1 MWIKTLQEAKSS-PDTQDLYCLNESSKnIPLANLQIPNCG 39
Cdd:pfam16920   7 RWLQLWQEEGLAgLGTQQLYCLNDGSK-IPLQSMNIPNCG 45

Fifth domain (immunoglobulin-like) of Trk receptor TrkB; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the fifth domain of Trk receptor, TrkB, an immunoglobulin (Ig)-like domain which binds to neurotrophin. The Trk family of receptors are tyrosine kinase receptors, which mediate the trophic effects of the neurotrophin Nerve Growth Factor (NGF) family. Trks are activated by dimerization, leading to autophosphorylation of intracellular tyrosine residues, and triggering the signal transduction pathway. TrkB shares significant sequence homology and domain organization with TrkA and TrkC. The first three domains are leucine-rich domains while the fourth and fifth domains are Ig-like domains playing a part in ligand binding. TrKB is recognized by brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-4. In some cell systems NT-3 can activate TrkA and TrkB receptors. TrKB transcripts are found throughout multiple structures of the central and peripheral nervous systems. This group belongs to the I-set of IgSF domains

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842 130 APTITFLESPTSDHHWCIPFTVKGNPKPALQWFYNGAILNESKYICTKIHVTNHTEYHGCLQLDNPTHMNNGDYTLIAKN 209
Cdd:cd05855     1 PPTITFLELPTRDHHWCIPFTVKGNPKPTLQWFHEGAILNESEYICTKIHVINNTEYHGCLQLDNPTHLNNGIYTLVAKN 80

                          90
                  ....*....|....
gi 1610576842 210 EYGKDEKQISAHFM 223
Cdd:cd05855    81 EYGEDEKNVSAHFM 94

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842   48 PNLTVEEGKSITLSCSVAGDPVPNMYW--DVGNLVSKHMNET---SHTQGSLRITNISSDDSGkQISCVAENLVGEDQDS 122
Cdd:smart00410   2 PSVTVKEGESVTLSCEASGSPPPEVTWykQGGKLLAESGRFSvsrSGSTSTLTISNVTPEDSG-TYTCAATNSSGSASSG 80

                   ....*
gi 1610576842  123 VNLTV 127
Cdd:smart00410  81 TTLTV 85

Leucine rich repeat C-terminal motif; This entry represents the Leucine Rich Repeat C-terminal (LRRCT) capping motif from TRK receptors.

                          10        20        30        40
                  ....*....|....*....|....*....|....*....|
gi 1610576842   1 MWIKTLQEAKSS-PDTQDLYCLNESSKnIPLANLQIPNCG 39
Cdd:pfam16920   7 RWLQLWQEEGLAgLGTQQLYCLNDGSK-IPLQSMNIPNCG 45

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

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|..
gi 1610576842  147 IPFTVKGNPKPALQWFYNGAILNESKyicTKIHVTNHTeYHGCLQLDNPTHMNNGDYTLIAKNEYGKDEKQI 218
Cdd:smart00410  14 LSCEASGSPPPEVTWYKQGGKLLAES---GRFSVSRSG-STSTLTISNVTPEDSGTYTCAATNSSGSASSGT 81

Fifth domain (immunoglobulin-like) of Trk receptor TrkB; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the fifth domain of Trk receptor, TrkB, an immunoglobulin (Ig)-like domain which binds to neurotrophin. The Trk family of receptors are tyrosine kinase receptors, which mediate the trophic effects of the neurotrophin Nerve Growth Factor (NGF) family. Trks are activated by dimerization, leading to autophosphorylation of intracellular tyrosine residues, and triggering the signal transduction pathway. TrkB shares significant sequence homology and domain organization with TrkA and TrkC. The first three domains are leucine-rich domains while the fourth and fifth domains are Ig-like domains playing a part in ligand binding. TrKB is recognized by brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-4. In some cell systems NT-3 can activate TrkA and TrkB receptors. TrKB transcripts are found throughout multiple structures of the central and peripheral nervous systems. This group belongs to the I-set of IgSF domains

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842 130 APTITFLESPTSDHHWCIPFTVKGNPKPALQWFYNGAILNESKYICTKIHVTNHTEYHGCLQLDNPTHMNNGDYTLIAKN 209
Cdd:cd05855     1 PPTITFLELPTRDHHWCIPFTVKGNPKPTLQWFHEGAILNESEYICTKIHVINNTEYHGCLQLDNPTHLNNGIYTLVAKN 80

                          90
                  ....*....|....
gi 1610576842 210 EYGKDEKQISAHFM 223
Cdd:cd05855    81 EYGEDEKNVSAHFM 94

Immunoglobulin I-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  49 NLTVEEGKSITLSCSVAGDPVPNMYWDVGNlvsKHMNETSHTQ-------GSLRITNISSDDSGKqISCVAENLVGEDQD 121
Cdd:pfam07679   9 DVEVQEGESARFTCTVTGTPDPEVSWFKDG---QPLRSSDRFKvtyeggtYTLTISNVQPDDSGK-YTCVATNSAGEAEA 84

                  ....*.
gi 1610576842 122 SVNLTV 127
Cdd:pfam07679  85 SAELTV 90

Third immunoglobulin (Ig)-like domain in Robo (roundabout) receptors; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the third immunoglobulin (Ig)-like domain in Robo (roundabout) receptors. Robo receptors play a role in the development of the central nervous system (CNS), and are receptors of Slit protein. Slit is a repellant secreted by the neural cells in the midline. Slit acts through Robo to prevent most neurons from crossing the midline from either side. Three mammalian Robo homologs (Robo1, Robo2, Robo3), and three mammalian Slit homologs (Slit-1,Slit-2, Slit-3), have been identified. Commissural axons, which cross the midline, express low levels of Robo; longitudinal axons, which avoid the midline, express high levels of Robo. Robo1, Robo2, and Robo3 are expressed by commissural neurons in the vertebrate spinal cord and Slit-1, Slit-2, and Slit-3 are expressed at the ventral midline. Robo-3 is a divergent member of the Robo family which instead of being a positive regulator of Slit responsiveness, antagonizes Slit responsiveness in precrossing axons. The Slit-Robo interaction is mediated by the second leucine-rich repeat (LRR) domain of Slit and the two N-terminal Ig domains of Robo, Ig1 and Ig2. The primary Robo binding site for Slit2 has been shown by surface plasmon resonance experiments and mutational analysis to be the Ig1 domain, while the Ig2 domain has been proposed to harbor a weak secondary binding site. This group belongs to the I-set of IgSF domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. 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 1610576842  49 NLTVEEGKSITLSCSVAGDPVPNMYW--DVGNL-VSKHMNETSHtqgSLRITNISSDDSGKQIsCVAENLVGEDQDSVNL 125
Cdd:cd05725     6 NQVVLVDDSAEFQCEVGGDPVPTVRWrkEDGELpKGRYEILDDH---SLKIRKVTAGDMGSYT-CVAENMVGKIEASATL 81

                  ..
gi 1610576842 126 TV 127
Cdd:cd05725    82 TV 83

Fourth Ig-like domain from smooth muscle myosin light chain kinase and similar domains ; a member of the I-set of IgSF domains; The members here are composed of the fourth immunoglobulin (Ig)-like domain from smooth muscle myosin light chain kinase (MYLK) and similar domains. The Ig superfamily (IgSF) is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. 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. Unlike the V-set, one of the distinctive features of I-set domains is the lack of a C" strand. The structure of this group shows that the fourth Ig-like domain from myosin light chain kinase lacks this strand and thus belongs to the I-set of the IgSF. I-set domains are found in several cell adhesion molecules (such as VCAM, ICAM, and MADCAM), and are also present in numerous other diverse protein families, including several tyrosine-protein kinase receptors, the hemolymph protein hemolin, the muscle proteins titin, telokin, and twitchin, the neuronal adhesion molecule axonin-1, and the signaling molecule semaphorin 4D that is involved in axonal guidance, immune function and angiogenesis.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  41 PSANLAAPNLTVEEGKSITLSCSVAGDPVPNMYWdvgNLVSKHMN-ETSHTQ-----GSLRITNISSDDSGkQISCVAEN 114
Cdd:cd20976     2 PSFSSVPKDLEAVEGQDFVAQCSARGKPVPRITW---IRNAQPLQyAADRSTceagvGELHIQDVLPEDHG-TYTCLAKN 77

                          90
                  ....*....|...
gi 1610576842 115 LVGEDQDSVNLTV 127
Cdd:cd20976    78 AAGQVSCSAWVTV 90

Leucine rich repeat C-terminal motif; This entry represents the Leucine Rich Repeat C-terminal (LRRCT) capping motif from TRK receptors.

                          10        20        30        40
                  ....*....|....*....|....*....|....*....|
gi 1610576842   1 MWIKTLQEAKSS-PDTQDLYCLNESSKnIPLANLQIPNCG 39
Cdd:pfam16920   7 RWLQLWQEEGLAgLGTQQLYCLNDGSK-IPLQSMNIPNCG 45

Immunoglobulin domain of human Synaptic Adhesion-Like Molecule 5 (SALM5) and similar proteins; member of the I-set of IgSF domains; This group contains the immunoglobulin domain of human Synaptic Adhesion-Like Molecule 5 (SALM5) and similar proteins. The SALM (for synaptic adhesion-like molecules; also known as Lrfn for leucine-rich repeat and fibronectin type III domain containing) family of adhesion molecules consists of five known members: SALM1/Lrfn2, SALM2/Lrfn1, SALM3/Lrfn4, SALM4/Lrfn3, and SALM5/Lrfn5. SALMs share a similar domain structure, containing leucine-rich repeats (LRRs), an immunoglobulin (Ig) domain, and a fibronectin III (FNIII) domain, followed by a transmembrane domain and a C-terminal PDZ-binding motif. SALM5 is implicated in autism spectrum disorders (ASDs) and schizophrenia, induces presynaptic differentiation in contacting axons. SALM5 interacts with the Ig domains of LAR (Leukocyte common Antigen-Related) family receptor protein tyrosine phosphatases (LAR-RPTPs; LAR, PTPdelta, and PTPsigma). In addition, PTPdelta is implicated in ASDs, ADHD, bipolar disorder, and restless leg syndrome. Studies have shown that LAR-RPTPs are novel and splicing-dependent presynaptic ligands for SALM5, and that they mediate SALM5-dependent presynaptic differentiation. Furthermore, SALM5 maintains AMPA receptor (AMPAR)-mediated excitatory synaptic transmission through mechanisms involving the interaction of SALM5 with LAR-RPTPs. This group belongs to the I-set of immunoglobulin superfamily (IgSF) domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. 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 1610576842  48 PNLTVEEGKSITLSCSVAGDPVPNMYWDV--GNLVSKHMNETSHTQGSLRITNISSDDSGkQISCVAENLVGEDQDSVNL 125
Cdd:cd05764     8 HELRVLEGQRATLRCKARGDPEPAIHWISpeGKLISNSSRTLVYDNGTLDILITTVKDTG-AFTCIASNPAGEATARVEL 86

                  ..
gi 1610576842 126 TV 127
Cdd:cd05764    87 HI 88

Immunoglobulin (Ig)-like I-set domain of Neural Cell Adhesion Molecule 1 (NCAM-1); The members here are composed of the fourth Ig domain of Neural Cell Adhesion Molecule 1(NCAM-1). NCAM plays important roles in the development and regeneration of the central nervous system, in synaptogenesis and neural migration. NCAM mediates cell-cell and cell-substratum recognition and adhesion via homophilic (NCAM-NCAM) and heterophilic (NCAM-non-NCAM) interactions. NCAM is expressed as three major isoforms having different intracellular extensions. The extracellular portion of NCAM has five N-terminal Ig-like domains and two fibronectin type III domains. The double zipper adhesion complex model for NCAM homophilic binding involves Ig1, Ig2, and Ig3. By this model, Ig1 and Ig2 mediate dimerization of NCAM molecules situated on the same cell surface (cis interactions), and Ig3 domains mediate interactions between NCAM molecules expressed on the surface of opposing cells (trans interactions), through binding to the Ig1 and Ig2 domains. The adhesive ability of NCAM is modulated by the addition of polysialic acid chains to the fifth Ig-like domain. One of the unique features of I-set domains is the lack of a C" strand. The structures of this group show that the Ig domain lacks this strand and thus is a member of the I-set of Ig domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  46 AAPNLTVEEGKS-------ITLSCSVAGDPVPNMYWDVG--NLVSK------HMNETSHTQ-GSLRITNISSDDSGKQIs 109
Cdd:cd05869     1 AKPKITYVENQTameleeqITLTCEASGDPIPSITWRTStrNISSEektldgHIVVRSHARvSSLTLKYIQYTDAGEYL- 79

                          90
                  ....*....|....*...
gi 1610576842 110 CVAENLVGEDQDSVNLTV 127
Cdd:cd05869    80 CTASNTIGQDSQSMYLEV 97

Immunoglobulin domain; Members of the immunoglobulin superfamily are found in hundreds of proteins of different functions. Examples include antibodies, the giant muscle kinase titin and receptor tyrosine kinases. Immunoglobulin-like domains may be involved in protein-protein and protein-ligand interactions.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  45 LAAPNLTVEEGKSITLSCSV-AGDPVPNMYWDVGNLVS-----KHMNETSHTQGSLRITNISSDDSGKqISCVAENLVGE 118
Cdd:pfam00047   1 SAPPTVTVLEGDSATLTCSAsTGSPGPDVTWSKEGGTLieslkVKHDNGRTTQSSLLISNVTKEDAGT-YTCVVNNPGGS 79

                  ....*..
gi 1610576842 119 DQDSVNL 125
Cdd:pfam00047  80 ATLSTSL 86

Third immunoglobulin (Ig) domain of contactin; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the third immunoglobulin (Ig) domain of contactins. Contactins are neural cell adhesion molecules and are comprised of six Ig domains followed by four fibronectin type III (FnIII) domains anchored to the membrane by glycosylphosphatidylinositol. The first four Ig domains form the intermolecular binding fragment, which arranges as a compact U-shaped module via contacts between Ig domains 1 and 4, and between Ig domains 2 and 3. Contactin-2 (TAG-1, axonin-1) may play a part in the neuronal processes of neurite outgrowth, axon guidance and fasciculation, and neuronal migration. This group also includes contactin-1 and contactin-5. The different contactins show different expression patterns in the central nervous system. During development and in adulthood, contactin-2 is transiently expressed in subsets of central and peripheral neurons. Contactin-5 is expressed specifically in the rat postnatal nervous system, peaking at about 3 weeks postnatal, and a lack of contactin-5 (NB-2) results in an impairment of neuronal activity in the rat auditory system. Contactin-5 is highly expressed in the adult human brain in the occipital lobe and in the amygdala. Contactin-1 is differentially expressed in tumor tissues and may, through a RhoA mechanism, facilitate invasion and metastasis of human lung adenocarcinoma. This group belongs to the I-set of IgSF domains.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*.
gi 1610576842  55 GKSITLSCSVAGDPVPNMYWD--VGNLVSKHMNETShtQGSLRITNISSDDSGKqISCVAENLVGEDQDSVNLTVH 128
Cdd:cd04968    16 GQTVTLECFALGNPVPQIKWRkvDGSPSSQWEITTS--EPVLEIPNVQFEDEGT-YECEAENSRGKDTVQGRIIVQ 88

Immunoglobulin (Ig)-like I-set domain of Neural Cell Adhesion Molecule 1 (NCAM-1) and similar proteins; The members here are composed of the fourth immunoglobulin (Ig)-like domain of Neural Cell Adhesion Molecule (NCAM-1). NCAM plays important roles in the development and regeneration of the central nervous system, in synaptogenesis and neural migration. NCAM mediates cell-cell and cell-substratum recognition and adhesion via homophilic (NCAM-NCAM), and heterophilic (NCAM-non-NCAM), interactions. NCAM is expressed as three major isoforms having different intracellular extensions. The extracellular portion of NCAM has five N-terminal Ig-like domains and two fibronectin type III domains. The double zipper adhesion complex model for NCAM homophilic binding involves Ig1, Ig2, and Ig3. By this model, Ig1 and Ig2 mediate dimerization of NCAM molecules situated on the same cell surface (cis interactions), and Ig3 domains mediate interactions between NCAM molecules expressed on the surface of opposing cells (trans interactions), through binding to the Ig1 and Ig2 domains. The adhesive ability of NCAM is modulated by the addition of polysialic acid chains to the fifth Ig-like domain. Also included in this group is NCAM-2 (also known as OCAM/mamFas II and RNCAM) NCAM-2 is differentially expressed in the developing and mature olfactory epithelium (OE). One of the unique features of I-set domains is the lack of a C" strand. The structures of this group show that the Ig domain lacks this strand and thus is a member of the I-set of Ig domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  49 NLTVEEGKSITLSCSVAGDPVPNMYWDV-------------GNLVSKhmneTSHTQGSLRITNISSDDSGKQIsCVAENL 115
Cdd:cd05732    10 NQTAVELEQITLTCEAEGDPIPEITWRRatrgisfeegdldGRIVVR----GHARVSSLTLKDVQLTDAGRYD-CEASNR 84

                          90
                  ....*....|..
gi 1610576842 116 VGEDQDSVNLTV 127
Cdd:cd05732    85 IGGDQQSMYLEV 96

Immunoglobulin (Ig)-like domain of myotilin, palladin, and myopalladin; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig)-like domain in myotilin, palladin, and myopalladin. Myotilin, palladin, and myopalladin function as scaffolds that regulate actin organization. Myotilin and myopalladin are most abundant in skeletal and cardiac muscle; palladin is ubiquitously expressed in the organs of developing vertebrates and plays a key role in cellular morphogenesis. The three family members each interact with specific molecular partners with all three binding to alpha-actinin; In addition, palladin also binds to vasodilator-stimulated phosphoprotein (VASP) and ezrin, myotilin binds to filamin and actin, and myopalladin also binds to nebulin and cardiac ankyrin repeat protein (CARP). This group belongs to the I-set of IgSF domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. 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 1610576842  50 LTVEEGKSITLSCSVAGDPVPNMYWDV-GNLV---SKH---MNET-SHtqgSLRITNISSDDSGKQIsCVAENLVGEDQD 121
Cdd:cd05744    10 LEVQEGRLCRFDCKVSGLPTPDLFWQLnGKPVrpdSAHkmlVRENgRH---SLIIEPVTKRDAGIYT-CIARNRAGENSF 85

                  ....*.
gi 1610576842 122 SVNLTV 127
Cdd:cd05744    86 NAELVV 91

Fourth immunoglobulin (Ig)-like domain of hemolin, and similar domains; a member of the I-set of IgSF domains; The members here are composed of the fourth immunoglobulin (Ig)-like domain of hemolin and similar proteins. Hemolin, an insect immunoglobulin superfamily (IgSF) member containing four Ig-like domains, is a lipopolysaccharide-binding immune protein induced during bacterial infection. Hemolin shares significant sequence similarity with the first four Ig-like domains of the transmembrane cell adhesion molecules (CAMs) of the L1 family. 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. The fourth Ig-like domain of hemolin is a member of the I-set Ig domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. Like the V-set domains, members of the I-set have a discontinuous A strand but lack a C" strand. I-set domains are found in several cell adhesion molecules (such as VCAM, ICAM, and MADCAM), and are also present in numerous other diverse protein families, including several tyrosine-protein kinase receptors, the muscle proteins titin, telokin, and twitchin, the neuronal adhesion molecule axonin-1, and the signaling molecule semaphorin 4D that is involved in axonal guidance, immune function and angiogenesis.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 1610576842 147 IPFTVKGNPKPALQWFYNGAILNESKYictKIHVTNHTeyhgcLQLDNPTHMNNGDYTLIAKNEYGKDEKQISAH 221
Cdd:cd20978    21 LPCQVTGVPQPKITWLHNGKPLQGPME---RATVEDGT-----LTIINVQPEDTGYYGCVATNEIGDIYTETLLH 87

Immunoglobulin domain I1 of the titin I-band and similar proteins; a member of the I-set of IgSF domains; The members here are composed of the immunoglobulin domain I1 of the titin I-band and similar proteins. Titin is a key component in the assembly and functioning of vertebrate striated muscles. By providing connections at the level of individual microfilaments, it contributes to the fine balance of forces between the two halves of the sarcomere. The Ig superfamily (IgSF) is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. The two sheets are linked together by a conserved disulfide bond between B strand and F strand. 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. The Ig I1 domain of the titin I-band is a member of the I-set Ig domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. Like the V-set Ig domains, members of the I-set have a discontinuous A strand but lack a C" strand. I-set domains are found in several cell adhesion molecules (such as VCAM, ICAM, and MADCAM), and are also present in numerous other diverse protein families, including several tyrosine-protein kinase receptors, the hemolymph protein hemolin, the muscle proteins titin, telokin, and twitchin, the neuronal adhesion molecule axonin-1, and the signaling molecule semaphorin 4D that is involved in axonal guidance, immune function and angiogenesis.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  50 LTVEEGKSITLSCSVAGDPVPNMYW-------DVGNLVSKHMNETSHTQGSLRITNISSDDSGkQISCVAENLVGEDQDS 122
Cdd:cd20951    10 HTVWEKSDAKLRVEVQGKPDPEVKWykngvpiDPSSIPGKYKIESEYGVHVLHIRRVTVEDSA-VYSAVAKNIHGEASSS 88

                  ....*
gi 1610576842 123 VNLTV 127
Cdd:cd20951    89 ASVVV 93

Fifth immunoglobulin domain of the Drosophila melanogaster Dscam protein, and similar domains; a member of the I-set of IgSF domains; The members here are composed of the fifth immunoglobulin domain of the Drosophila melanogaster Down syndrome cell adhesion molecule (DSCAM) protein and similar proteins. Down syndrome cell adhesion molecule (DSCAM) is a cell adhesion molecule that plays critical roles in neural development, including axon guidance and branching, axon target recognition, self-avoidance and synaptic formation. DSCAM belongs to the immunoglobulin superfamily and contributes to defects in the central nervous system in Down syndrome patients. Vertebrate DSCAMs differ from Drosophila Dscam1 in that they lack the extensive alternative splicing that occurs in the insect gene. Drosophila melanogaster Dscam has 38,016 isoforms generated by the alternative splicing of four variable exon clusters, which allows every neuron in the fly to display a distinctive set of Dscam proteins on its cell surface. Drosophila Dscam1 is a cell-surface protein that plays important roles in neural development and axon tiling of neurons. It is shown that thousands of isoforms bind themselves through specific homophilic (self-binding) interactions, a process which mediates cellular self-recognition. Drosophila Dscam2 is also alternatively spliced and plays a key role in the development of two visual system neurons, monopolar cells L1 and L2. This group is a member of the I-set Ig domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. 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 1610576842  48 PNLTVEEGKSITLSCSVAGDPVPNMYWDVGN--LVSKHmNETSHTQGSLRITNI-SSDDSGkQISCVAENLVGE-DQDSV 123
Cdd:cd20958     8 GNLTAVAGQTLRLHCPVAGYPISSITWEKDGrrLPLNH-RQRVFPNGTLVIENVqRSSDEG-EYTCTARNQQGQsASRSV 85

                  ....
gi 1610576842 124 NLTV 127
Cdd:cd20958    86 FVKV 89

Fourth immunoglobulin domain of the Drosophila melanogaster Dscam protein, and similar domains; a member of the I-set of IgSF domains; The members here are composed of the fourth immunoglobulin domain of the Drosophila melanogaster Down syndrome cell adhesion molecule (DSCAM) protein and similar proteins. Down syndrome cell adhesion molecule (DSCAM) is a cell adhesion molecule that plays critical roles in neural development, including axon guidance and branching, axon target recognition, self-avoidance and synaptic formation. DSCAM belongs to the immunoglobulin superfamily and contributes to defects in the central nervous system in Down syndrome patients. Vertebrate DSCAMs differ from Drosophila Dscam1 in that they lack the extensive alternative splicing that occurs in the insect gene. Drosophila melanogaster Dscam has 38,016 isoforms generated by the alternative splicing of four variable exon clusters, which allows every neuron in the fly to display a distinctive set of Dscam proteins on its cell surface. Drosophila Dscam1 is a cell-surface protein that plays important roles in neural development and axon tiling of neurons. It is shown that thousands of isoforms bind themselves through specific homophilic (self-binding) interactions, a process which mediates cellular self-recognition. Drosophila Dscam2 is also alternatively spliced and plays a key role in the development of two visual system neurons, monopolar cells L1 and L2. This group is a member of the I-set Ig domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. 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 1610576842  48 PNLTVEEGKSITLSCSVAGDPVPNMYWD-------------VGNLVSKHMNETSHtqgsLRITNISSDDSGkQISCVAEN 114
Cdd:cd20956     9 SEQTLQPGPSVSLKCVASGNPLPQITWTldgfpipesprfrVGDYVTSDGDVVSY----VNISSVRVEDGG-EYTCTATN 83

                          90
                  ....*....|...
gi 1610576842 115 LVGEDQDSVNLTV 127
Cdd:cd20956    84 DVGSVSHSARINV 96

Third immunoglobulin (Ig)-like domain of peroxidasin; The members here are composed of the third immunoglobulin (Ig)-like domain in peroxidasin. Peroxidasin has a peroxidase domain and interacting extracellular motifs containing four Ig-like domains. It has been suggested that peroxidasin is secreted and has functions related to the stabilization of the extracellular matrix. It may play a part in various other important processes such as removal and destruction of cells which have undergone programmed cell death and protection of the organism against non-self.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 1610576842  54 EGKSITLSCSVAGDPVPNMYWDVG----NLVSKHMNETShtqGSLRITNISSDDSGkQISCVAENLVGEDQDSVNLTV 127
Cdd:cd05745     1 EGQTVDFLCEAQGYPQPVIAWTKGgsqlSVDRRHLVLSS---GTLRISRVALHDQG-QYECQAVNIVGSQRTVAQLTV 74

Immunoglobulin (Ig)-like domain in neuregulins; The members here are composed of the immunoglobulin (Ig)-like domain in neuregulins (NRGs). NRGs are signaling molecules which participate in cell-cell interactions in the nervous system, breast, heart, and other organ systems, and are implicated in the pathology of diseases including schizophrenia, multiple sclerosis, and breast cancer. There are four members of the neuregulin gene family (NRG-1, NRG-2, NRG-3, and NRG-4). The NRG-1 protein, binds to and activates the tyrosine kinases receptors ErbB3 and ErbB4, initiating signaling cascades. The other NRGs proteins bind one or the other or both of these ErbBs. NRG-1 has multiple functions: in the brain it regulates various processes such as radial glia formation and neuronal migration, dendritic development, and expression of neurotransmitters receptors, while in the peripheral nervous system NRG-1 regulates processes such as target cell differentiation, and Schwann cell survival. There are many NRG-1 isoforms which arise from the alternative splicing of mRNA. Less is known of the functions of the other NRGs. NRG-2 and NRG-3 are expressed predominantly in the nervous system. NRG-2 is expressed by motor neurons and terminal Schwann cells, and is concentrated near synaptic sites and may be a signal that regulates synaptic differentiation. NRG-4 has been shown to direct pancreatic islet cell development towards the delta-cell lineage.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  49 NLTVEEGKSITLSC-SVAGDPVPNMYW-DVGNLVSKHMNETSHTQGS-----LRITNISSDDSGkQISCVAENLVGEDQD 121
Cdd:cd05750     8 SQTVQEGSKLVLKCeATSENPSPRYRWfKDGKELNRKRPKNIKIRNKkknseLQINKAKLEDSG-EYTCVVENILGKDTV 86

                  ....*.
gi 1610576842 122 SVNLTV 127
Cdd:cd05750    87 TGNVTV 92

C-terminal immunoglobulin (Ig)-like domain of M-protein; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the C-terminal immunoglobulin (Ig)-like domain of M-protein (also known as myomesin-2). M-protein is a structural protein localized to the M-band, a transverse structure in the center of the sarcomere, and is a candidate for M-band bridges. M-protein is modular consisting mainly of repetitive IG-like and fibronectin type III (FnIII) domains and has a muscle-type specific expression pattern. M-protein is present in fast fibers.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  39 GLPSAnlaapnLTVEEGKSITLSCSVAGDPVPNMYW---DVGNLVSKHMNeTSHTQG---SLRITNISSDDSGKQISCVA 112
Cdd:cd05891     6 GLPDV------VTIMEGKTLNLTCTVFGNPDPEVIWfknDQDIELSEHYS-VKLEQGkyaSLTIKGVTSEDSGKYSINVK 78

                  ....*....
gi 1610576842 113 ENLVGEDQD 121
Cdd:cd05891    79 NKYGGETVD 87

Second Ig-like domain of the giant muscle protein titin Z1z2 in the sarcomeric Z-disk, and similar domains; a member of the I-set of IgSF domains; The members here are composed of the second immunoglobulin (Ig)-like domain of the giant muscle protein titin Z1z2 in the sarcomeric Z-disk and similar proteins. Titin is a key component in the assembly and functioning of vertebrate striated muscles. By providing connections at the level of individual microfilaments, it contributes to the fine balance of forces between the two halves of the sarcomere. The Ig superfamily (IgSF) is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. 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. Unlike the V-set, one of the distinctive features of I-set domains is the lack of a C" strand. The structure of the titin Z1z2 lacks this strand and thus it belongs to the I-set of the IgSF. I-set domains are found in several cell adhesion molecules (such as VCAM, ICAM, and MADCAM), and are also present in numerous other diverse protein families, including several tyrosine-protein kinase receptors, the hemolymph protein hemolin, the muscle proteins titin, telokin, and twitchin, the neuronal adhesion molecule axonin-1, and the signaling molecule semaphorin 4D that is involved in axonal guidance, immune function and angiogenesis.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  51 TVEEGKSITLSCSVAGDPVPNMYWDV-GNLVSKHMNETSHTQG---SLRITNISSDDSGKqISCVAENLVGEDQDSVNLT 126
Cdd:cd20972    12 EVAEGSKVRLECRVTGNPTPVVRWFCeGKELQNSPDIQIHQEGdlhSLIIAEAFEEDTGR-YSCLATNSVGSDTTSAEIF 90

                  .
gi 1610576842 127 V 127
Cdd:cd20972    91 V 91

C-terminal immunoglobulin-like domain of the myosin-associated giant protein kinase Twitchin, and similar domains; member of the I-set IgSF domains; The members here are composed of the C-terminal immunoglobulin-like domain of the myosin-associated giant protein kinase Twitchin and similar proteins, including Caenorhabditis elegans and Aplysia californica Twitchin, Drosophila melanogaster Projectin, and similar proteins. These are very large muscle proteins containing multiple immunoglobulin (Ig)-like and fibronectin type III (FN3) domains and a single kinase domain near the C-terminus. In humans these proteins are called Titin. The Ig superfamily (IgSF) is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. 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. The Ig-like domain of the Twitchin is a member of the I-set IgSF domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. Like the V-set Ig domains, members of the I-set have a discontinuous A strand but lack a C" strand. I-set domains are found in several cell adhesion molecules (such as VCAM, ICAM, and MADCAM), and are also present in numerous other diverse protein families, including several tyrosine-protein kinase receptors, the hemolymph protein hemolin, the muscle proteins (titin, telokin, and twitchin), the neuronal adhesion molecule axonin-1, and the signaling molecule semaphorin 4D.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  50 LTVEEGKSITLSCSVAGDPVPNMYWDV-GNLVSKHMNETSHTQG---SLRITNISSDDSGkQISCVAENLVGEDQDSVNL 125
Cdd:cd20949     9 TTVKEGQSATILCEVKGEPQPNVTWHFnGQPISASVADMSKYRIladGLLINKVTQDDTG-EYTCRAYQVNSIASDMQER 87

                  ..
gi 1610576842 126 TV 127
Cdd:cd20949    88 TV 89

Third immunoglobulin (Ig)-like domain of Neural Cell Adhesion Molecule 1 (NCAM-1); member of the I-set of IgSF domains; The members here are composed of the third immunoglobulin (Ig)-like domain of Neural Cell Adhesion Molecule (NCAM-1). NCAM plays important roles in the development and regeneration of the central nervous system, in synaptogenesis and neural migration. NCAM mediates cell-cell and cell-substratum recognition and adhesion via homophilic (NCAM-NCAM), and heterophilic (NCAM-non-NCAM), interactions. NCAM is expressed as three major isoforms having different intracellular extensions. The extracellular portion of NCAM has five N-terminal Ig-like domains and two fibronectin type III domains. The double zipper adhesion complex model for NCAM homophilic binding involves Ig1, Ig2, and Ig3. By this model, Ig1 and Ig2 mediate dimerization of NCAM molecules situated on the same cell surface (cis interactions), and Ig3 domains mediate interactions between NCAM molecules expressed on the surface of opposing cells (trans interactions) through binding to the Ig1 and Ig2 domains. The adhesive ability of NCAM is modulated by the addition of polysialic acid chains to the fifth Ig-like domain.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  49 NLTVEEGKSITLSCSVAGDPVPNMYW-DVGNLVSKHMNETSHTQGS--LRITNISSDDSGkQISCVAENLVGEDQDSVNL 125
Cdd:cd05730    12 NATANLGQSVTLACDADGFPEPTMTWtKDGEPIESGEEKYSFNEDGseMTILDVDKLDEA-EYTCIAENKAGEQEAEIHL 90

                  ..
gi 1610576842 126 TV 127
Cdd:cd05730    91 KV 92

Second immunoglobulin (Ig)-like domain of a Follistatin-related protein 5, and similar domains; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin (Ig)-like domain found in human Follistatin-related protein 5 (FSTL5) and a follistatin-like molecule encoded by the CNS-related Mahya gene. Mahya genes have been retained in certain Bilaterian branches during evolution. They are conserved in Hymenoptera and Deuterostomes, but are absent from other metazoan species such as fruit fly and nematode. Mahya proteins are secretory, with a follistatin-like domain (Kazal-type serine/threonine protease inhibitor domain and EF-hand calcium-binding domain), two Ig-like domains, and a novel C-terminal domain. Mahya may be involved in learning and memory and in processing of sensory information in Hymenoptera and vertebrates. Follistatin is a secreted, multidomain protein that binds activins with high affinity and antagonizes their signaling.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  53 EEGKSITLSCSVAGDPVPNMYW-----DVGNLVSKHMneTSHTQGS-LRITNISSDDSGKqISCVAENLVGEDQDSVNLT 126
Cdd:cd05736    13 EPGVEASLRCHAEGIPLPRVQWlkngmDINPKLSKQL--TLIANGSeLHISNVRYEDTGA-YTCIAKNEGGVDEDISSLF 89

                  .
gi 1610576842 127 V 127
Cdd:cd05736    90 V 90

Fourth Ig domain of the neural cell adhesion molecule contactin-2, and similar domains; The members here are composed of the fourth Ig domain of the neural cell adhesion molecule contactin-2. Contactins are comprised of six Ig domains followed by four fibronectin type III (FnIII) domains anchored to the membrane by glycosylphosphatidylinositol. Contactin-2 (also called TAG-1, axonin-1) facilitates cell adhesion by homophilic binding between molecules in apposed membranes. The first four Ig domains form the intermolecular binding fragment which arranges as a compact U-shaped module by contacts between Ig domains 1 and 4, and domains 2 and 3. It has been proposed that a linear zipper-like array forms, from contactin-2 molecules alternatively provided by the two apposed membranes.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|...
gi 1610576842  55 GKSITLSCSVAGDPVPNMYWDVGNLVSKHMNETSHTQGSLRITNISSDDSGkQISCVAENLVGEDQDSVNLTV 127
Cdd:cd05728    14 GSSLRWECKASGNPRPAYRWLKNGQPLASENRIEVEAGDLRITKLSLSDSG-MYQCVAENKHGTIYASAELAV 85

Immunoglobulin (Ig)-like domain of titin and similar proteins; The members here are composed of the immunoglobulin (Ig)-like domain found in titin-like proteins and similar proteins. Titin (also called connectin) is a fibrous sarcomeric protein specifically found in vertebrate striated muscle. Titin is a giant protein; depending on isoform composition, it ranges from 2970 to 3700 kDa, and is of a length that spans half a sarcomere. Titin largely consists of multiple repeats of Ig-like and fibronectin type 3 (FN-III)-like domains. Titin connects the ends of myosin thick filaments to Z disks and extends along the thick filament to the H zone. It appears to function similarly to an elastic band, keeping the myosin filaments centered in the sarcomere during muscle contraction or stretching. Within the sarcomere, titin is also attached to or is associated with myosin binding protein C (MyBP-C). MyBP-C appears to contribute to the generation of passive tension by titin and like titin has repeated Ig-like and FN-III domains. Also included in this group are worm twitchin and insect projectin, thick filament proteins of invertebrate muscle which also have repeated Ig-like and FN-III domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  50 LTVEEGKSITLSCSVAGDPVPNMYW---DVGNLVSKHMN-ETSHTQGSLRITNISSDDSGKQISCVaENLVGEDQDSVNL 125
Cdd:cd05748     2 IVVRAGESLRLDIPIKGRPTPTVTWskdGQPLKETGRVQiETTASSTSLVIKNAKRSDSGKYTLTL-KNSAGEKSATINV 80

                  ..
gi 1610576842 126 TV 127
Cdd:cd05748    81 KV 82

Third immunoglobulin (Ig)-like domain of the L1 cell adhesion molecule (CAM), and similar domains; The members here are composed of the third immunoglobulin (Ig)-like domain of the L1 cell adhesion molecule (CAM). L1 belongs to the L1 subfamily of cell adhesion molecules (CAMs) and is comprised of an extracellular region having six Ig-like domains and five fibronectin type III domains, a transmembrane region and an intracellular domain. L1 is primarily expressed in the nervous system and is involved in its development and function. L1 is associated with an X-linked recessive disorder, X-linked hydrocephalus, MASA syndrome, and spastic paraplegia type 1, that involves abnormalities of axonal growth. This group also contains the chicken neuron-glia cell adhesion molecule, Ng-CAM and human neurofascin.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  49 NLTVEEGKSITLSCSVAGDPVPNMYW-DVGNLVSKHMNETSHTQGSLRITNISSDDSGkQISCVAENLVGEDQDSVNLTV 127
Cdd:cd05731     4 STMVLRGGVLLLECIAEGLPTPDIRWiKLGGELPKGRTKFENFNKTLKIENVSEADSG-EYQCTASNTMGSARHTISVTV 82

Second immunoglobulin (Ig)-like domain of a Follistatin-related protein 5, and similar domains; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin (Ig)-like domain found in human Follistatin-related protein 5 (FSTL5) and a follistatin-like molecule encoded by the CNS-related Mahya gene. Mahya genes have been retained in certain Bilaterian branches during evolution. They are conserved in Hymenoptera and Deuterostomes, but are absent from other metazoan species such as fruit fly and nematode. Mahya proteins are secretory, with a follistatin-like domain (Kazal-type serine/threonine protease inhibitor domain and EF-hand calcium-binding domain), two Ig-like domains, and a novel C-terminal domain. Mahya may be involved in learning and memory and in processing of sensory information in Hymenoptera and vertebrates. Follistatin is a secreted, multidomain protein that binds activins with high affinity and antagonizes their signaling.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 1610576842 151 VKGNPKPALQWFYNGAILN--ESKYICTkihVTNHTEYHgclqLDNPTHMNNGDYTLIAKNEYGKDEkQISAHFM 223
Cdd:cd05736    24 AEGIPLPRVQWLKNGMDINpkLSKQLTL---IANGSELH----ISNVRYEDTGAYTCIAKNEGGVDE-DISSLFV 90

Fifth immunoglobulin (Ig)-like domain of the carcinoembryonic antigen (CEA) related cell adhesion molecule 5 (CEACAM5) and similar domains; member of the C2-set IgSF domains; The members here are composed of the fifth immunoglobulin (Ig)-like domain of the carcinoembryonic antigen (CEA) related cell adhesion molecule 5 (CEACAM5) and similar domains. The CEA family is a group of anchored or secreted glycoproteins, expressed by epithelial cells, leukocytes, endothelial cells and placenta. The CEA family is divided into the CEACAM and pregnancy-specific glycoprotein (PSG) subfamilies. Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5), also known as CD66e (Cluster of Differentiation 66e), is a cell surface glycoprotein that plays a role in cell adhesion, intracellular signaling and tumor progression. Diseases associated with CEACAM5 include lung cancer and rectum cancer. 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. This group belongs to the C2-set of IgSF domains, having A, B, and E strands in one beta-sheet and A', G, F, C' in the other. Unlike other Ig domain sets, the C2-set lacks the D strand.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1610576842  48 PNLTVEEGKSITLSCSVAGDPVPNMYWDV--GNLVSKHmnetshtqgSLRITNISSDDSGkQISCVAENLVGEDQDSVNL 125
Cdd:cd20948     3 SDTYYLSGENLNLSCHAASNPPAQYSWTIngTFQTSSQ---------ELFLPAITENNEG-TYTCSAHNSLTGKNISLVL 72

                  ..
gi 1610576842 126 TV 127
Cdd:cd20948    73 SV 74

Fourth immunoglobulin (Ig)-like domain of L1, Ng-CAM (Neuron-glia CAM cell adhesion molecule), and NrCAM (Ng-CAM-related); The members here are composed of the fourth immunoglobulin (Ig)-like domain of L1, Ng-CAM (Neuron-glia CAM cell adhesion molecule), and NrCAM (Ng-CAM-related). These proteins belong to the L1 subfamily of cell adhesion molecules (CAMs) and are comprised of an extracellular region having six Ig-like domains and five fibronectin type III domains, a transmembrane region and an intracellular domain. These molecules are primarily expressed in the nervous system. L1 is associated with an X-linked recessive disorder, X-linked hydrocephalus, MASA syndrome, or spastic paraplegia type 1, that involves abnormalities of axonal growth.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|...
gi 1610576842  48 PNLTVEEGKSITLSCSVAGDPVPNMYWDV-GNLVSKHMNETSHT--QGSLRITNISSDDSGkQISCVAENLVG 117
Cdd:cd04978     7 PSLVLSPGETGELICEAEGNPQPTITWRLnGVPIEPAPEDMRRTvdGRTLIFSNLQPNDTA-VYQCNASNVHG 78