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 21686977  29 TENVTVAEGGVAEITCRLHQYDGSIVVIQNPARQTLFFNGTRALKDERFQLEEFSPRRVRIRLSDARLEDEGGYFCQLYT 108
Cdd:cd05881   3 TEDVTVVEGEVATISCRVKNSDDSVIQLLNPNRQTIYFRDFRPLKDSRFQLVNFSSSELRVSLTNVSISDEGRYFCQLYT 82

                        90
                ....*....|..
gi 21686977 109 EDTHHQIATLTV 120
Cdd:cd05881  83 DPPQEAYTTITV 94

putative band 4.1 homologues' binding motif;

                           10
                   ....*....|....*....
gi 21686977    344 MVWCSVRQKGSYLTHEASG 362
Cdd:smart00294   1 MYRYKHRDEGSYHTHEPKG 19

First (N-terminal) immunoglobulin (Ig)-like domain of nectin-like molecule 2; member of the V-set of Ig superfamily (IgSF) domains; The members here are composed of the N-terminal immunoglobulin (Ig)-like domain of nectin-like molecule-2, Necl-2 (also known as cell adhesion molecule 1 (CADM1), SynCAM1, IGSF4A, Tslc1, sgIGSF, and RA175). Nectin-like molecules have similar domain structures to those of nectins. At least five nectin-like molecules have been identified (Necl-1 - Necl-5). They all have an extracellular region containing three Ig-like domains, a transmembrane region, and a cytoplasmic region. The N-terminal Ig-like domain of the extracellular region, belongs to the V-type subfamily of Ig domains, is essential to cell-cell adhesion, and plays a part in the interaction with the envelope glycoprotein D of various viruses. Necl-2 has Ca(2+)-independent homophilic and heterophilic cell-cell adhesion activity. Necl-2 is expressed in a wide variety of tissues and is a putative tumour suppressor gene, which is downregulated in aggressive neuroblastoma.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977  29 TENVTVAEGGVAEITCRLHQYDGSIVVIQNPARQTLFFNGTRALKDERFQLEEFSPRRVRIRLSDARLEDEGGYFCQLYT 108
Cdd:cd05881   3 TEDVTVVEGEVATISCRVKNSDDSVIQLLNPNRQTIYFRDFRPLKDSRFQLVNFSSSELRVSLTNVSISDEGRYFCQLYT 82

                        90
                ....*....|..
gi 21686977 109 EDTHHQIATLTV 120
Cdd:cd05881  83 DPPQEAYTTITV 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 21686977    231 SQAVVREGDTLVLTCAVTGNPRPnQIRWNRGNESL---PERAEAVGE----TLTLPGLVSADNGTYTCEASNKHGHARAL 303
Cdd:smart00410   2 PSVTVKEGESVTLSCEASGSPPP-EVTWYKQGGKLlaeSGRFSVSRSgstsTLTISNVTPEDSGTYTCAATNSSGSASSG 80

                   ....*
gi 21686977    304 YVLVV 308
Cdd:smart00410  81 TTLTV 85

CD80-like C2-set immunoglobulin domain; These domains belong to the immunoglobulin superfamily.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977   124 PENPVVEVReqaVEGGEVELSCLVPRSRPAATLRWYRDRKELKGVSSSQE---NGKVWSVASTVRFRVDRKDDGGIIICE 200
Cdd:pfam08205   3 IEPPASLLE---GEGPEVVATCSSAGGKPAPRITWYLDGKPLEAAETSSEqdpESGLVTVTSELKLVPSRSDHGQSLTCQ 79

                  ....*.
gi 21686977   201 AQNQAL 206
Cdd:pfam08205  80 VSYGAL 85

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 21686977    32 VTVAEGGVAEITCRLH-QYDGSIVVI----QNPARQTLF------FNGTRALKDERFQLEEFSPR-RVRIRLSDARLEDE 99
Cdd:pfam07686   6 VTVALGGSVTLPCTYSsSMSEASTSVywyrQPPGKGPTFliayysNGSEEGVKKGRFSGRGDPSNgDGSLTIQNLTLSDS 85

                          90       100
                  ....*....|....*....|...
gi 21686977   100 GGYFCQLYTEDTHHQIATLTVLV 122
Cdd:pfam07686  86 GTYTCAVIPSGEGVFGKGTRLTV 108

envelope glycoprotein C; Provisional

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977  100 GGYFCQLYTEDTHHQIATLTVLVAPENPVVEVREQAVEGGEV-ELSCLVPRSRP--AATLRWYRDRKELKGVSSSQENGK 176
Cdd:PHA03273 211 GVYVWSLYAKNGTLVNSTSVTVSTYNAPLVDLSVHPSLKGENyRAVCVVASYFPhsSVKLRWYKNAKEVDFTKYVTNASS 290

                         90       100       110       120       130       140       150       160
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977  177 VW-----SVASTVRFRVDRKDD-GGIIICEAQNQALPSGHSKQTQYVL-DVQYSPTARIHasqavVREGDTLvltCAVTG 249
Cdd:PHA03273 291 VWvdgliTRISTLSIPVDPDEEyTPSLRCSIEWYRDEVSFARIAKAGTpSVFVAPTVSVT-----VEDGDAV---CTAKC 362

                        170       180       190       200       210       220       230       240
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977  250 NPRPN-QIRWNRGNE--SLPERAEAVGETLTLPGLV--------SADNG--TYTCEASNKHGHARALYVLVVYDPGAVVE 316
Cdd:PHA03273 363 VPSTGvFVSWSVNDHlpGVPSQDMTTGVCSSHPGLVnmqsrrplSEENGerEYSCIIEGYPDGLPMFSDTVVYDASPIVE 442

                        250       260
                 ....*....|....*....|....*..
gi 21686977  317 AQ---TSVPYAIVGGILALLVFLIICV 340
Cdd:PHA03273 443 DEpvlTSIIAVTCGAAALALVVLITAV 469

Second immunoglobulin (Ig)-like domain of the nectin-like molecules Necl-1 - Necl-4; member of the I-set of Ig superfamily domains; The members here are composed of the second immunoglobulin (Ig)-like domain of the nectin-like molecules Necl-1 (also known as cell adhesion molecule 3 or CADM3), Necl-2 (also known as CADM1), Necl-3 (also known as CADM2) and Necl-4 (also known as CADM4). These nectin-like molecules have similar domain structures to those of nectins. At least five nectin-like molecules have been identified (Necl-1 through Necl-5). These have an extracellular region containing three Ig-like domains, one transmembrane region, and one cytoplasmic region. The N-terminal Ig-like domain of the extracellular region belongs to the V-type subfamily of Ig domains, is essential to cell-cell adhesion, and plays a part in the interaction with the envelope glycoprotein D of various viruses. Necl-1 and Necl-2 have Ca(2+)-independent homophilic and heterophilic cell-cell adhesion activity. Necl-1 is specifically expressed in neural tissue and is important to the formation of synapses, axon bundles, and myelinated axons. Necl-2 is expressed in a wide variety of tissues, and is a putative tumour suppressor gene, which is downregulated in aggressive neuroblastoma. Necl-3 has been shown to accumulate in tissues of the central and peripheral nervous system, where it is expressed in ependymal cells and myelinated axons. It is observed at the interface between the axon shaft and the myelin sheath. Necl-4 is expressed on Schwann cells, and plays a key part in initiating peripheral nervous system (PNS) myelination. Necl-4 participates in cell-cell adhesion and is proposed to play a role in tumor suppression.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977 121 LVAPENPVVEVREQAV-EGGEVELSCLVPRSRPAATLRWYRDRKELKGVSSSQENG--KVWSVASTVRFRVDRKDDGGII 197
Cdd:cd05761   1 LGVPEKPVITGFTSPVvEGDEITLTCTTSGSKPAADIRWFKNDKELKGVKEVQESGagKTFTVTSTLRFRVDRDDDGVAV 80

                        90       100
                ....*....|....*....|...
gi 21686977 198 ICEAQNQALPsGHSKQTQYVLDV 220
Cdd:cd05761  81 ICRVDHESLT-STPKQTQQVLEV 102

First (N-terminal) immunoglobulin (Ig)-like domain of the nectin-like molecules; member of the V-set of Ig superfamily (IgSF) domains; The members here are composed of the N-terminal immunoglobulin (Ig)-like domain of the nectin-like molecules Necl-1 (also known as cell adhesion molecule 3 (CADM3)), Necl-2 (CADM1), Necl-3 (CADM2), and similar proteins. At least five nectin-like molecules have been identified (Necl-1 to Necl-5). They all have an extracellular region containing three Ig-like domains, a transmembrane region, and a cytoplasmic region. The N-terminal Ig-like domain of the extracellular region belongs to the V-type subfamily of Ig domains, is essential to cell-cell adhesion, and plays a part in the interaction with the envelope glycoprotein D of various viruses. Necl-1, Necl-2, and Necl-3 have Ca(2+)-independent homophilic and heterophilic cell-cell adhesion activity. Necl-1 is specifically expressed in neural tissue, and is important to the formation of synapses, axon bundles, and myelinated axons. Necl-2 is expressed in a wide variety of tissues and is a putative tumour suppressor gene which is downregulated in aggressive neuroblastoma. Necl-3 accumulates in central and peripheral nervous system tissue and has been shown to selectively interact with oligodendrocytes. This group also contains Class-I MHC-restricted T-cell-associated molecule (CRTAM), whose expression pattern is consistent with its expression in Class-I MHC-restricted T-cells.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977  29 TENVTVAEGGVAEITCRLHQYDGSIVVIQNPARQTLFFNGTRALKDERFQLEEFSPRRVRIRLSDARLEDEGGYFCQLYT 108
Cdd:cd05717   3 TQDVTVVEGETLTLKCQVSLRDDSSLQWLNPNGQTIYFNDKRALRDSRYQLLNHSASELSISVSNVTLSDEGVYTCLHYT 82

                        90
                ....*....|..
gi 21686977 109 EDTHHQIATLTV 120
Cdd:cd05717  83 DPVSTKKVTVTV 94

Second immunoglobulin (Ig)-like domain of nectin-like molecule-3 (Necl-3); member of the I-set of Ig superfamily domains; The members here are composed of the second immunoglobulin (Ig)-like domain of nectin-like molecule-3 (Necl-3; also known as cell adhesion molecule 2 (CADM2)). Nectin-like molecules have similar domain structures to those of nectins. At least five nectin-like molecules have been identified (Necl-1 through Necl-5). These have an extracellular region containing three Ig-like domains, one transmembrane region, and one cytoplasmic region. Necl-3 has been shown to accumulate in tissues of the central and peripheral nervous system where it is expressed in ependymal cells and myelinated axons. It is observed at the interface between the axon shaft and the myelin sheath. Ig domains are likely to participate in ligand binding and recognition.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977 120 VLVAPENPVVEVREQAV-EGGEVELSCLVPRSRPAATLRWYRDRKELKGVSSSQE---NGKVWSVASTVRFRVDRKDDGG 195
Cdd:cd05884   1 VLGVPEKPQISGFTSPVmEGDHIQLTCKTSGSKPAADIRWFKNDKEVKDVKYLKAedaNRKTFTVSSSLDFHVDRDDDGV 80

                        90       100
                ....*....|....*....|....*
gi 21686977 196 IIICEAQNQALPSGHSKQTQyVLDV 220
Cdd:cd05884  81 AITCRVDHESLTATPQIAMQ-VLEI 104

First (N-terminal) immunoglobulin (Ig)-like domain of nectin-like molecule-1 (Necl-1); member of the V-set of Ig superfamily (IgSF) domains; The members here are composed of the N-terminal immunoglobulin (Ig)-like domain of nectin-like molecule-1, Necl-1 (also known as celll adhesion molecule 3 (CADM3), SynCAM2, or IGSF4). Nectin-like molecules have similar domain structures to those of nectins. At least five nectin-like molecules have been identified (Necl-1 - Necl-5). They all have an extracellular region containing three Ig-like domains, a transmembrane region, and a cytoplasmic region. The N-terminal Ig-like domain of the extracellular region belongs to the V-type subfamily of Ig domains, is essential to cell-cell adhesion, and plays a part in the interaction with the envelope glycoprotein D of various viruses. Necl-1 has Ca(2+)-independent homophilic and heterophilic cell-cell adhesion activity. Necl-1 is specifically expressed in neural tissue and is important to the formation of synapses, axon bundles, and myelinated axons.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977  29 TENVTVAEGGVAEITCRLHQYDGSIVVIQNPARQTLFFNGTRALKDERFQLEEFSPRRVRIRLSDARLEDEGGYFCQLYT 108
Cdd:cd05882   4 TQDETVAVGGTVTLKCGVKEHDNSSLQWSNTAQQTLYFGEKRALRDNRIQLVKSTPTELIISISNVQLSDEGEYTCSIFT 83

                        90
                ....*....|..
gi 21686977 109 EDTHHQIATLTV 120
Cdd:cd05882  84 MPVRTAKATVTV 95

Second immunoglobulin (Ig)-like domain of nectin-like molcule-1 (Necl-1); member of the I-set of Ig superfamily domains; The members here are composed of the second immunoglobulin (Ig)-like domain of nectin-like molcule-1 (Necl-1; also known as cell adhesion molecule3 (CADM3)). These nectin-like molecules have similar domain structures to those of nectins. At least five nectin-like molecules have been identified (Necl-1 through Necl-5). These have an extracellular region containing three Ig-like domains, one transmembrane region, and one cytoplasmic region. The N-terminal Ig-like domain of the extracellular region belongs to the V-type subfamily of Ig domains is essential to cell-cell adhesion and plays a part in the interaction with the envelope glycoprotein D of various viruses. Necl-1 and Necl-2 have Ca(2+)-independent homophilic and heterophilic cell-cell adhesion activity. Necl-1 is specifically expressed in neural tissue and is important to the formation of synapses, axon bundles, and myelinated axons. Necl-2 is expressed in a wide variety of tissues and is a putative tumour suppressor gene which is downregulated in aggressive neuroblastoma. Ig domains are likely to participate in ligand binding and recognition.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977 124 PENPVVEVREQAV-EGGEVELSCLVPRSRPAATLRWYRDRKELKGVSSS-QE--NGKVWSVASTVRFRVDRKDDGGIIIC 199
Cdd:cd07705   4 PQKPQITGYESAFkEKDKAKLRCTSSGSKPAANIKWRKGDQELEGAPTSvQEdgNGKTFTVSSSVEFQVTREDDGAEITC 83

                        90       100
                ....*....|....*....|.
gi 21686977 200 EAQNQALpSGHSKQTQYVLDV 220
Cdd:cd07705  84 SVGHESL-HDSDRSTSQRIEV 103

Immunoglobulin I-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977   224 PTARIHASQAVVREGDTLVLTCAVTGNPRPnQIRWNRGNESLPE------RAEAVGETLTLPGLVSADNGTYTCEASNKH 297
Cdd:pfam07679   1 PKFTQKPKDVEVQEGESARFTCTVTGTPDP-EVSWFKDGQPLRSsdrfkvTYEGGTYTLTISNVQPDDSGKYTCVATNSA 79

                  .
gi 21686977   298 G 298
Cdd:pfam07679  80 G 80

agrin-responsive first immunoglobulin-like domains (Ig1) of the MuSK ectodomain; a member of the I-set of IgSF domains; The members here are composed of the first immunoglobulin-like domains (Ig1) of the Muscle-specific kinase (MuSK). MuSK is a receptor tyrosine kinase specifically expressed in skeletal muscle, where it plays a central role in the formation and maintenance of the neuromuscular junction (NMJ). MuSK is activated by agrin, a neuron-derived heparan sulfate proteoglycan. The activation of MUSK in myotubes regulates the formation of NMJs through the regulation of different processes including the specific expression of genes in subsynaptic nuclei, the reorganization of the actin cytoskeleton and the clustering of the acetylcholine receptors (AChR) in the postsynaptic membrane. 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 MuSK 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 21686977 231 SQAVVREGDTLVLTCAVTGNPRPnQIRWNRGNESLPERAEAV-----GETLTLPGLVSADNGTYTCEASNK-HGHARALY 304
Cdd:cd20970  10 FTVTAREGENATFMCRAEGSPEP-EISWTRNGNLIIEFNTRYivrenGTTLTIRNIRRSDMGIYLCIASNGvPGSVEKRI 88

                ....
gi 21686977 305 VLVV 308
Cdd:cd20970  89 TLQV 92

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
                ....*....|....*....|....*....|....*....|....*....|....*....|....
gi 21686977 241 LVLTCAVTGNPRPnQIRWNRGNESLPE------RAEAVGETLTLPGLVSADNGTYTCEASNKHG 298
Cdd:cd00096   1 VTLTCSASGNPPP-TITWYKNGKPLPPssrdsrRSELGNGTLTISNVTLEDSGTYTCVASNSAG 63

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 21686977 230 ASQAVVREGDTLVLTCAVTGNPRPnQIRWNRGNESLP---ERAEAVGETLTLPGLVSADNGTYTCEASNKHGHARALYVL 306
Cdd:cd05731   2 ESSTMVLRGGVLLLECIAEGLPTP-DIRWIKLGGELPkgrTKFENFNKTLKIENVSEADSGEYQCTASNTMGSARHTISV 80

                ..
gi 21686977 307 VV 308
Cdd:cd05731  81 TV 82

Immunoglobulin domain; This domain contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977   228 IHASQAVVREGDTLVLTCAVTGNPRPNqIRWNRGNESLPERAEavgetLTLPGLVSADNGTYTCEASNKHGHARALYVLV 307
Cdd:pfam13895   4 LTPSPTVVTEGEPVTLTCSAPGNPPPS-YTWYKDGSAISSSPN-----FFTLSVSAEDSGTYTCVARNGRGGKVSNPVEL 77

                  .
gi 21686977   308 V 308
Cdd:pfam13895  78 T 78

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
                ....*....|....*....|....*....|....*....|....*....|....*....|...
gi 21686977 238 GDTLVLTCAVTGNPRPNqIRWNRGNESLP--ERAEAVGETLTLPGLVSADNGTYTCEASNKHG 298
Cdd:cd05728  14 GSSLRWECKASGNPRPA-YRWLKNGQPLAseNRIEVEAGDLRITKLSLSDSGMYQCVAENKHG 75

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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 21686977 234 VVREGDTLVLTCAVTGNPRPNqIRWNRGNESLPE-RAEAVGE-TLTLPGLVSADNGTYTCEASNKHGHARALYVLVV 308
Cdd:cd05725   8 VVLVDDSAEFQCEVGGDPVPT-VRWRKEDGELPKgRYEILDDhSLKIRKVTAGDMGSYTCVAENMVGKIEASATLTV 83

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
                ....*....|....*....|....*....|....*....|....*....|....*....|...
gi 21686977 238 GDTLVLTCAVTGNPRPnQIRWNRGNESLPERAEAV--GETLTLPGLVSADNGTYTCEASNKHG 298
Cdd:cd04968  16 GQTVTLECFALGNPVP-QIKWRKVDGSPSSQWEITtsEPVLEIPNVQFEDEGTYECEAENSRG 77

Immunoglobulin (Ig)-like domain of vascular endothelial growth factor (VEGF) receptor (R) and similar proteins; member of the I-set of IgSF domains; The members here are composed of the immunoglobulin (Ig)-like domain of vascular endothelial growth factor (VEGF) receptor (R) and related proteins. The VEGFRs have an extracellular component with seven Ig-like domains, a transmembrane segment, and an intracellular tyrosine kinase domain interrupted by a kinase-insert domain. The VEGFR family consists of three members: VEGFR-1 (Flt-1), VEGFR-2 (KDR/Flk-1) and VEGFR-3 (Flt-4). VEGF-A interacts with both VEGFR-1 and VEGFR-2. VEGFR-1 binds strongest to VEGF; VEGF-2 binds more weakly. VEGFR-3 appears not to bind VEGF, but binds other members of the VEGF family (VEGF-C and -D). VEGFRs bind VEGFs with high affinity with the IG-like domains. VEGF-A is important to the growth and maintenance of vascular endothelial cells and to the development of new blood- and lymphatic-vessels in physiological and pathological states. VEGFR-2 is a major mediator of the mitogenic, angiogenic, and microvascular permeability-enhancing effects of VEGF-A. VEGFR-1 may play an inhibitory part in these processes by binding VEGF and interfering with its interaction with VEGFR-2. VEGFR-1 has a signaling role in mediating monocyte chemotaxis. VEGFR-1 and VEGFR-2 may mediate a chemotactic and a survival signal in hematopoietic stem cells or leukemia cells. VEGFR-3 has been shown to be involved in tumor angiogenesis and growth. This group also contains alpha-type platelet-derived growth factor receptor precursor (PDGFR)-alpha (CD140a), and PDGFR-beta (CD140b). PDGFRs alpha and beta have an extracellular component with five Ig-like domains, a transmembrane segment, and a cytoplasmic portion that has protein tyrosine kinase activity.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977 219 DVQYSPTARihasQAVVREGDTLVLTCAVTGNPRPN-QIRW-------NRGNESLPERAEAVGE------TLTLPGLVSA 284
Cdd:cd05742   2 DLELSPNAE----PTVLPQGETLVLNCTANVNLNEVvDFQWtypsekeGKLALLKPDIKVDWSEpgefvsTLTIPEATLK 77

                        90
                ....*....|
gi 21686977 285 DNGTYTCEAS 294
Cdd:cd05742  78 DSGTYTCAAR 87

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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 21686977 234 VVREGDTLVLTCAVTGNPrPNQIRWNrgnesLPERAEAVGETLTLPGLVSADNGTYTCEASNK-HGHARALYVLVVY 309
Cdd:cd20948   6 YYLSGENLNLSCHAASNP-PAQYSWT-----INGTFQTSSQELFLPAITENNEGTYTCSAHNSlTGKNISLVLSVTV 76

Sixth 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 sixth 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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977 238 GDTLVLTCAVTGNPRPNQIRWNRGNESLPE-------RAEAVGETLTLPGLVSADNGTYTCEASNKHGHA 300
Cdd:cd20959  17 GMRAQLHCGVPGGDLPLNIRWTLDGQPISDdlgitvsRLGRRSSILSIDSLEASHAGNYTCHARNSAGSA 86

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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|...
gi 21686977 235 VREGDTLVLTCAVTGNPRPnQIRWNRGNESLP---------ERAEAVgeTLTLPGLVSADNGTYTCEASNKHG 298
Cdd:cd05891  13 IMEGKTLNLTCTVFGNPDP-EVIWFKNDQDIElsehysvklEQGKYA--SLTIKGVTSEDSGKYSINVKNKYG 82

Immunoglobulin (Ig)-like domain of human carcinoembryonic antigen (CEA) related cell adhesion molecule (CEACAM) domains 2, 4, and 6, and similar domains; The members here are composed of the second, fourth, and sixth immunoglobulin (Ig)-like domains in human carcinoembryonic antigen (CEA) related cell adhesion molecule (CEACAM) protein subfamily. 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. This group represents the CEACAM subfamily. CEACAM1 has many important cellular functions; it is a cell adhesion molecule and a signaling molecule that regulates the growth of tumor cells, an angiogenic factor, and a receptor for bacterial and viral pathogens, including mouse hepatitis virus (MHV). In mice, four isoforms of CEACAM1 generated by alternative splicing have either two [D1, D4] or four [D1-D4] Ig-like domains on the cell surface.

                        10        20        30        40        50        60        70
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*.
gi 21686977 224 PTARIHASQAVvREGDTLVLTCAVTGNPrpNQIRWNRGNESLPE----RAEAVGETLTLPGLVSADNGTYTCEASN 295
Cdd:cd05740   2 PFISSNNSNPV-EDKDAVTLTCEPETQN--TSYLWWFNGQSLPVtprlTLSNGNRTLTLLNVTREDAGAYQCEISN 74

Immunoglobulin (Ig)-like domain of the human basement membrane heparan sulfate proteoglycan perlecan and similar proteins; The members here are composed of the immunoglobulin (Ig)-like domain of the human basement membrane heparan sulfate proteoglycan perlecan, also known as HSPG2, and similar proteins. Perlecan consists of five domains: domain I has three putative heparan sulfate attachment sites, domain II has four LDL receptor-like repeats, and one Ig-like repeat, domain III resembles the short arm of laminin chains, domain IV has multiple Ig-like repeats (21 repeats in human perlecan), and domain V resembles the globular G domain of the laminin A chain and internal repeats of EGF. Perlecan may participate in a variety of biological functions including cell binding, LDL-metabolism, basement membrane assembly and selective permeability, calcium binding, and growth- and neurite-promoting activities.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977 238 GDTLVLTCAVTGNPRPnQIRW--NRGNESLPERAEAVGE----TLTLPGLVSADNGTYTCEASNKHGharalYVLVVydP 311
Cdd:cd05743   1 GETVEFTCVATGVPTP-IINWrlNWGHVPDSARVSITSEggygTLTIRDVKESDQGAYTCEAINTRG-----MVFGI--P 72

                ....*
gi 21686977 312 GAVVE 316
Cdd:cd05743  73 DGILT 77

Immunoglobulin (Ig)-like domain found in Perlecan and similar proteins; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the third immunoglobulin (Ig)-like domain found in Perlecan. Perlecan is a large multi-domain heparin sulfate proteoglycan, important in tissue development and organogenesis. Perlecan can be represented as 5 major portions; its fourth major portion (domain IV) is a tandem repeat of immunoglobulin-like domains (Ig2-Ig15) which can vary in size due to alternative splicing. Perlecan binds many cellular and extracellular ligands. Its domain IV region has many binding sites. Some of these have been mapped at the level of individual Ig-like domains, including a site restricted to the Ig5 domain for heparin/sulfatide, a site restricted to the Ig3 domain for nidogen-1 and nidogen-2, a site restricted to Ig4-5 for fibronectin, and sites restricted to Ig2 and to Ig13-15 for fibulin-2. 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
                ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 21686977 235 VREGDTLVLTC-AVTGNPRPNqIRWNRGNESLPERAEAVGETLTLPGLVSADNGTYTCEASN 295
Cdd:cd05754  13 VRPGADVSFICrAKSKSPAYT-LVWTRVNGTLPSRAMDFNGILTIRNVQLSDAGTYVCTGSN 73

Second immunoglobulin (Ig)-like domain of fibroblast growth factor (FGF) receptor; member of the I-set of IgSF domains; The members here are composed of the second immunoglobulin (Ig)-like domain of fibroblast growth factor (FGF) receptor. FGF receptors bind FGF signaling polypeptides. FGFs participate in multiple processes such as morphogenesis, development, and angiogenesis. FGFs bind to four FGF receptor tyrosine kinases (FGFR1, FGFR2, FGFR3, FGFR4). Receptor diversity is controlled by alternative splicing producing splice variants with different ligand binding characteristics and different expression patterns. FGFRs have an extracellular region comprised of three IG-like domains, a single transmembrane helix, and an intracellular tyrosine kinase domain. Ligand binding and specificity reside in the Ig-like domains 2 and 3, and the linker region that connects these two. FGFR activation and signaling depend on FGF-induced dimerization, a process involving cell surface heparin or heparin sulfate proteoglycans.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 21686977 227 RIHASQAvvreGDTLVLTCAVTGNPRPNqIRWNRGNESLPERAEAVG-------ETLTLPGLVSADNGTYTCEASNKHGH 299
Cdd:cd05857  12 KLHAVPA----ANTVKFRCPAAGNPTPT-MRWLKNGKEFKQEHRIGGykvrnqhWSLIMESVVPSDKGNYTCVVENEYGS 86

                ....*....
gi 21686977 300 ARALYVLVV 308
Cdd:cd05857  87 INHTYHLDV 95

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 21686977 224 PTARIHASQ--AVVREGDTLVLTCAVTGNPRPnQIRWNRGNESLPERAEAV-----GETLTLPGLVSADNGTYTCEASNK 296
Cdd:cd05730   2 PTIRARQSEvnATANLGQSVTLACDADGFPEP-TMTWTKDGEPIESGEEKYsfnedGSEMTILDVDKLDEAEYTCIAENK 80

                        90
                ....*....|...
gi 21686977 297 HGHARALYVLVVY 309
Cdd:cd05730  81 AGEQEAEIHLKVF 93

Second immunoglobulin (Ig)-like domain of Axl/Tyro3 family receptor tyrosine kinases (RTKs); member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin (Ig)-like domain in the Axl/Tyro3 family of receptor tyrosine kinases (RTKs). This family includes Axl (also known as Ark, Ufo, and Tyro7), Tyro3 (also known as Sky, Rse, Brt, Dtk, and Tif), and Mer (also known as Nyk, c-Eyk, and Tyro12). Axl/Tyro3 family receptors have an extracellular portion with two Ig-like domains followed by two fibronectin-types III (FNIII) domains, a membrane-spanning single helix, and a cytoplasmic tyrosine kinase domain. Axl, Tyro3, and Mer are widely expressed in adult tissues, though they show higher expression in the brain, lymphatic and vascular systems, and testis. Axl, Tyro3, and Mer bind the vitamin K dependent protein Gas6 with high affinity, and in doing so activate their tyrosine kinase activity. Axl/Gas6 signaling may play a part in cell adhesion processes, prevention of apoptosis, and cell proliferation.

                        10        20        30        40        50
                ....*....|....*....|....*....|....*....|....*....|....*.
gi 21686977 243 LTCAVTGNPRPNQIRWNRGNESLPERAEAVGETLTLPGLvsADNGTYTCEASNKHG 298
Cdd:cd05749  19 LTCQAVGPPEPVEILWWQGGSPLGGPPAPSPSVLNVPGL--NETTKFSCEAHNAKG 72

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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 21686977 235 VREGDTLVLTCAVTGNPRPnQIRWNRGNESLPERAE-AVGETLTLPGLV----------SADNGTYTCEASNKHGHA 300
Cdd:cd20956  13 LQPGPSVSLKCVASGNPLP-QITWTLDGFPIPESPRfRVGDYVTSDGDVvsyvnissvrVEDGGEYTCTATNDVGSV 88

Fourth immunoglobulin (Ig)-like domain in neogenin, and similar domains; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the fourth immunoglobulin (Ig)-like domain in neogenin and related proteins. Neogenin is a cell surface protein which is expressed in the developing nervous system of vertebrate embryos in the growing nerve cells. It is also expressed in other embryonic tissues, and may play a general role in developmental processes such as cell migration, cell-cell recognition, and tissue growth regulation. Included in this group is the tumor suppressor protein DCC which is deleted in colorectal carcinoma. DCC and neogenin each have four Ig-like domains followed by six fibronectin type III domains, a transmembrane domain, and an intracellular domain. 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 21686977 229 HASQAVVREGDTLVLTCAVTGNPRPNqIRWNR-GNESLP-ERAEAVGE-TLTLPGLVSADNGTYTCEASNKHGHARALYV 305
Cdd:cd05723   3 KPSNIYAHESMDIVFECEVTGKPTPT-VKWVKnGDVVIPsDYFKIVKEhNLQVLGLVKSDEGFYQCIAENDVGNAQASAQ 81

                ...
gi 21686977 306 LVV 308
Cdd:cd05723  82 LII 84