Second immunoglobulin (Ig) domain of nectin-3 and nectin-4 (poliovirus receptor related protein 4), and similar domains; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin (Ig) domain of nectin-3 (also known as poliovirus receptor related protein 3 or cluster of differentiation (CD) 113) and nectin-4 (poliovirus receptor related protein 4). Nectin-3 and nectin-4 belong to the nectin family comprised of four transmembrane glycoproteins (nectin-1 through -4). Nectins are synaptic cell adhesion molecules (CAMs) which facilitate adhesion and signaling at various intracellular junctions. Nectins form homophilic cis-dimers, followed by homophilic and heterophilic trans-dimers involved in cell-cell adhesion. Nectin-2 and nectin-3 localize at Sertoli-spermatid junctions where they form heterophilic trans-interactions between the cells that are essential for the formation and maintenance of the junctions and for spermatid development. Nectin-3 has also been shown to form a heterophilic trans-interaction with nectin-1 in ciliary epithelia, establishing the apex-apex adhesion between the pigment and non-pigment cell layers. Nectin-4 has recently been identified in several types of breast carcinoma and can be used as a histological and serological marker for breast cancer.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971 151 PTVSLIKGPDSLIDGGNETVAAICIAATGKPVAHIDWEGDLGEMESTTTSFPNETATIISQYKLFPTRFARGRRITCVVK 230
Cdd:cd07704    1 PLVSLNPGPALLIDGGNETLAASCTAETGKPAASVTWETDLGGMESSRTFEHNRTATVTSEYHLVPTRFANGRPLTCVVS 80

                         90
                 ....*....|....*.
gi 966924971 231 HPALEKDIRYSFILDI 246
Cdd:cd07704   81 HPALQQDIRITHILDV 96

Second immunoglobulin (Ig) domain of nectin-3 and nectin-4 (poliovirus receptor related protein 4), and similar domains; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin (Ig) domain of nectin-3 (also known as poliovirus receptor related protein 3 or cluster of differentiation (CD) 113) and nectin-4 (poliovirus receptor related protein 4). Nectin-3 and nectin-4 belong to the nectin family comprised of four transmembrane glycoproteins (nectin-1 through -4). Nectins are synaptic cell adhesion molecules (CAMs) which facilitate adhesion and signaling at various intracellular junctions. Nectins form homophilic cis-dimers, followed by homophilic and heterophilic trans-dimers involved in cell-cell adhesion. Nectin-2 and nectin-3 localize at Sertoli-spermatid junctions where they form heterophilic trans-interactions between the cells that are essential for the formation and maintenance of the junctions and for spermatid development. Nectin-3 has also been shown to form a heterophilic trans-interaction with nectin-1 in ciliary epithelia, establishing the apex-apex adhesion between the pigment and non-pigment cell layers. Nectin-4 has recently been identified in several types of breast carcinoma and can be used as a histological and serological marker for breast cancer.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971 151 PTVSLIKGPDSLIDGGNETVAAICIAATGKPVAHIDWEGDLGEMESTTTSFPNETATIISQYKLFPTRFARGRRITCVVK 230
Cdd:cd07704    1 PLVSLNPGPALLIDGGNETLAASCTAETGKPAASVTWETDLGGMESSRTFEHNRTATVTSEYHLVPTRFANGRPLTCVVS 80

                         90
                 ....*....|....*.
gi 966924971 231 HPALEKDIRYSFILDI 246
Cdd:cd07704   81 HPALQQDIRITHILDV 96

Third immunoglobulin domain of Nectin-like Protein-5, and similar domains; The members here are composed of the third immunoglobulin domain of Nectin-like Protein-5 (also known as Cluster of Differentiation 155 (CD155)). Nectin-like Protein-5 mediates NK (Natural Killer) cell adhesion and triggers NK cell effector functions. CD155 binds two different NK cell receptors: CD96 and CD226. These interactions accumulate at the cell-cell contact site, leading to the formation of a mature immunological synapse between NK cell and target cell. This may trigger adhesion and secretion of lytic granules and IFN-gamma and activate cytotoxicity of activated NK cells. CD155 may also promote NK cell-target cell modular exchange, and PVR transfer to the NK cell. This transfer is more important in some tumor cells expressing a lot of PVR, and may trigger fratricide NK cell activation, providing tumors with a mechanism of immunoevasion. Moreover, CD155 plays a role in mediating tumor cell invasion and migration.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971 250 PEVSVTGYDGNWFVGRKGVNLKCNADANPPPFKSVWSRLDGQWPDGLLASDNTLhFVHPLTFNYSGVYICKVTNSLGQRS 329
Cdd:cd20930    1 PEVSISGYDDNWYLGRNEATLTCDVRSNPEPTGYDWSTTSGPFPTSAVAQGPQL-LIHSVDRLVNTTFICTVTNAVGTGR 79

                 ....*..
gi 966924971 330 DQKVIYI 336
Cdd:cd20930   80 AEQTIFV 86

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971    45 PHVTAVWGKNVSLKCLIEVNETItQISWEKIHGKSSQtvavhhpqygfsvqgeYQGRVLFKNYSlNDATITLHNIGFSDS 124
Cdd:smart00410   2 PSVTVKEGESVTLSCEASGSPPP-EVTWYKQGGKLLA----------------ESGRFSVSRSG-STSTLTISNVTPEDS 63

                           90       100
                   ....*....|....*....|...
gi 966924971   125 GKYICkAVTFPLGNAQSSTTVTV 147
Cdd:smart00410  64 GTYTC-AATNSSGSASSGTTLTV 85

Immunoglobulin I-set domain;

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|..
gi 966924971  268 VNLKCNADANPPPfKSVWSRlDGQwpdgLLASDNTLHF----------VHPLTFNYSGVYICKVTNSLGQRS 329
Cdd:pfam07679  18 ARFTCTVTGTPDP-EVSWFK-DGQ----PLRSSDRFKVtyeggtytltISNVQPDDSGKYTCVATNSAGEAE 83

Second immunoglobulin (Ig) domain of nectin-3 and nectin-4 (poliovirus receptor related protein 4), and similar domains; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin (Ig) domain of nectin-3 (also known as poliovirus receptor related protein 3 or cluster of differentiation (CD) 113) and nectin-4 (poliovirus receptor related protein 4). Nectin-3 and nectin-4 belong to the nectin family comprised of four transmembrane glycoproteins (nectin-1 through -4). Nectins are synaptic cell adhesion molecules (CAMs) which facilitate adhesion and signaling at various intracellular junctions. Nectins form homophilic cis-dimers, followed by homophilic and heterophilic trans-dimers involved in cell-cell adhesion. Nectin-2 and nectin-3 localize at Sertoli-spermatid junctions where they form heterophilic trans-interactions between the cells that are essential for the formation and maintenance of the junctions and for spermatid development. Nectin-3 has also been shown to form a heterophilic trans-interaction with nectin-1 in ciliary epithelia, establishing the apex-apex adhesion between the pigment and non-pigment cell layers. Nectin-4 has recently been identified in several types of breast carcinoma and can be used as a histological and serological marker for breast cancer.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971 151 PTVSLIKGPDSLIDGGNETVAAICIAATGKPVAHIDWEGDLGEMESTTTSFPNETATIISQYKLFPTRFARGRRITCVVK 230
Cdd:cd07704    1 PLVSLNPGPALLIDGGNETLAASCTAETGKPAASVTWETDLGGMESSRTFEHNRTATVTSEYHLVPTRFANGRPLTCVVS 80

                         90
                 ....*....|....*.
gi 966924971 231 HPALEKDIRYSFILDI 246
Cdd:cd07704   81 HPALQQDIRITHILDV 96

Second immunoglobulin (Ig) domain of poliovirus receptor (PVR, also known as CD155 and Necl-5), and similar domains; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin (Ig) domain of poliovirus receptor (PVR, also known as CD155 and nectin-like protein 5 (Necl-5)) and similar proteins. Poliovirus (PV) binds to its cellular receptor (PVR/CD155) to initiate infection. CD155 is a membrane-anchored, single-span glycoprotein; its extracellular region has three Ig-like domains. There are four different isotypes of CD155 (referred to as alpha, beta, gamma, and delta), these result from alternate splicing of the CD155 mRNA, and have identical extracellular domains. CD155-beta and CD155-gamma are secreted, while CD155-alpha and CD155-delta are membrane-bound and function as PV receptors. The virus recognition site is contained in the amino-terminal domain, D1. Having the virus attachment site on the receptor distal from the plasma membrane may be important for successful initiation of infection of cells by the virus. CD155 binds in the poliovirus "canyon" and has a footprint similar to that of the intercellular adhesion molecule-1 receptor on human rhinoviruses. This group also includes the second Ig-like domain of nectin-1, also known as poliovirus receptor related protein(PVRL)1 or CD111.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971 151 PTVSLIKGPDSLIdGGNETVAAICIAATGKPVAHIDWEGDLGEMESTTTSFP-NETATIISQYKLFPTRFARGRRITCVV 229
Cdd:cd05719    1 PTNSLEGGPALLI-GGEPTLVATCISANGKPPASVTWETDLKGEASTTQVRGsNGTVTVTSRYRLVPSREADGQPLTCVV 79

                         90
                 ....*....|....*..
gi 966924971 230 KHPALEKDIRYSFILDI 246
Cdd:cd05719   80 EHPSLEKDQRISVTLNV 96

First immunoglobulin variable (IgV) domain of nectin-1, and similar domains; The members here are composed of the first immunoglobulin (Ig) domain of nectin-1 (also known as poliovirus receptor related protein 1 (PVRL1) or cluster of differentiation (CD) 111). Nectin-1 belongs to the nectin family comprised of four transmembrane glycoproteins (nectins-1 through -4). Nectins are synaptic cell adhesion molecules (CAMs) which facilitate adhesion and signaling at various intracellular junctions. Nectins form homophilic cis-dimers, followed by homophilic and heterophilic trans-dimers involved in cell-cell adhesion. In addition nectins heterophilically trans-interact with other CAMs such as nectin-like molecules (Necls), nectin-1 for example, has been shown to trans-interact with Necl-1. Nectins also interact with various other proteins, including the actin filament (F-actin)-binding protein, afadin. Mutation in the human nectin-1 gene is associated with cleft lip/palate ectodermal dysplasia syndrome (CLPED1). Nectin-1 is a major receptor for herpes simplex virus through interaction with the viral envelope glycoprotein D.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971  52 GKNVSLKCLI---EVNETITQISWEKIHGKSSQTVAVHHPQYGFSVQGEYQGRVLFKNYSLNDATITLHNIGFSDSGKYI 128
Cdd:cd05886   14 GTDVVLHCSFanpLPSVKITQVTWQKSTNGSKQNVAIYNPSMGVSVLPPYRERVTFLNPSFTDGTIRLSRLELEDEGVYI 93

                         90       100
                 ....*....|....*....|
gi 966924971 129 CKAVTFPLGNAQSSTTVTVL 148
Cdd:cd05886   94 CEFATFPTGNRESQLNLTVM 113

Third immunoglobulin domain of Nectin-like Protein-5, and similar domains; The members here are composed of the third immunoglobulin domain of Nectin-like Protein-5 (also known as Cluster of Differentiation 155 (CD155)). Nectin-like Protein-5 mediates NK (Natural Killer) cell adhesion and triggers NK cell effector functions. CD155 binds two different NK cell receptors: CD96 and CD226. These interactions accumulate at the cell-cell contact site, leading to the formation of a mature immunological synapse between NK cell and target cell. This may trigger adhesion and secretion of lytic granules and IFN-gamma and activate cytotoxicity of activated NK cells. CD155 may also promote NK cell-target cell modular exchange, and PVR transfer to the NK cell. This transfer is more important in some tumor cells expressing a lot of PVR, and may trigger fratricide NK cell activation, providing tumors with a mechanism of immunoevasion. Moreover, CD155 plays a role in mediating tumor cell invasion and migration.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971 250 PEVSVTGYDGNWFVGRKGVNLKCNADANPPPFKSVWSRLDGQWPDGLLASDNTLhFVHPLTFNYSGVYICKVTNSLGQRS 329
Cdd:cd20930    1 PEVSISGYDDNWYLGRNEATLTCDVRSNPEPTGYDWSTTSGPFPTSAVAQGPQL-LIHSVDRLVNTTFICTVTNAVGTGR 79

                 ....*..
gi 966924971 330 DQKVIYI 336
Cdd:cd20930   80 AEQTIFV 86

Second immunoglobulin (Ig) domain of Nectin-2 and Nectin-like protein 5, and similar domains; member of the C1-set of the Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin (Ig) domain of nectin-2 (also known as poliovirus receptor related protein 2 or Cluster of Differentiation 112 (CD112)), nectin-like protein 5 (CD155), and similar proteins. Nectins and Nectin-like molecules are a family of Ca(2+)-independent immunoglobulin-like transmembrane glycoproteins belonging to the class of adhesion receptors, consisting of nine members (nectins 1 through 4 and nectin-like proteins 1 through 5). Nectins are synaptic cell adhesion molecules (CAMs) which facilitate adhesion and signaling at various intracellular junctions. Nectins form homophilic cis-dimers, followed by homophilic and heterophilic trans-dimers involved in cell-cell adhesion. Nectin-2 and nectin-3 localize at Sertoli-spermatid junctions where they form heterophilic trans-interactions between the cells that are essential for the formation and maintenance of the junctions and for spermatid development. CD155 is the fifth member in the nectin-like molecule family, and functions as the receptor of poliovirus; therefore, CD155 is also referred to as Necl-5, or PVR. In contrast to all other family members, CD155 lacks self-adhesion capacity, yet it shares with nectins the feature to interact with other nectins. For instance, CD155 heterophilically trans-interacts with nectin-3, thereby contributing significantly to the establishment of adherens junctions between epithelial cells. This group belongs to the Constant 1 (C1)-set of IgSF domains, which has one beta-sheet that is formed by strands A-B-E-D and the other strands by G-F-C-C'.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 966924971 165 GGNETVAAICIAATGKPVAHIDWEGDLGEMESTT--TSFPNETATIISQYKLFPTRFARGRRITCVVKHPALEKD 237
Cdd:cd07703   13 GGIPVPVARCVSANGRPPARISWSSTLNGNANTTqvPGPDSGTVTVTSEYSLVPTPEANGKEVTCKVEHETLEEP 87

First immunoglobulin variable (IgV) domain of nectin-2, nectin-like protein 5, and similar domains; The members here are composed of the second immunoglobulin (Ig) domain of nectin-2 (also known as poliovirus receptor related protein 2 or Cluster of Differentiation 112 (CD112)), nectin-like protein 5 (CD155), and similar proteins. Nectins and Nectin-like molecules are a family of Ca(2+)-independent immunoglobulin-like transmembrane glycoproteins belonging to the class of adhesion receptors, consisting of nine members (nectins 1 through 4 and nectin-like proteins 1 through 5). Nectins are synaptic cell adhesion molecules (CAMs) which facilitate adhesion and signaling at various intracellular junctions. Nectins form homophilic cis-dimers, followed by homophilic and heterophilic trans-dimers involved in cell-cell adhesion. Nectin-2 and nectin-3 localize at Sertoli-spermatid junctions where they form heterophilic trans-interactions between the cells that are essential for the formation and maintenance of the junctions and for spermatid development. CD155 is the fifth member in the nectin-like molecule family, and functions as the receptor of poliovirus; therefore, CD155 is also referred to as Necl-5, or PVR. In contrast to all other family members, CD155 lacks self-adhesion capacity, yet it shares with nectins the feature to interact with other nectins. For instance, CD155 heterophilically trans-interacts with nectin-3, thereby contributing significantly to the establishment of adherens junctions between epithelial cells. This group belongs to the Constant 1 (C1)-set of IgSF domains, which has one beta-sheet that is formed by strands A-B-E-D and the other strands by G-F-C-C'.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971  41 IIVEPHVTAVWGKNVSLKCLIEVNE---TITQISWEKiHGkSSQTVAVHHPQYGFSVQGEyqGRVLF----KNYSLNDAT 113
Cdd:cd20989    3 VQVPPEVRGFLGGSVTLPCHLLPPNmvtHVSQVTWQR-HD-EHGSVAVFHPKQGPSFPES--ERLSFvaarLGAELRNAS 78

                         90       100       110
                 ....*....|....*....|....*....|....
gi 966924971 114 ITLHNIGFSDSGKYICKAVTFPLGNAQSSTTVTV 147
Cdd:cd20989   79 LAMFGLRVEDEGNYTCEFATFPQGSRSGDTWLRV 112

Second immunoglobulin (Ig) domain of nectin-1, and similar domains; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin (Ig) domain of nectin-1 (also known as poliovirus receptor related protein 1, or cluster of differentiation (CD) 111). Nectin-1 belongs to the nectin family comprised of four transmembrane glycoproteins (nectin-1 through -4). Nectins are synaptic cell adhesion molecules (CAMs) which facilitate adhesion and signaling at various intracellular junctions. Nectins form homophilic cis-dimers, followed by homophilic and heterophilic trans-dimers involved in cell-cell adhesion. Nectins also heterophilically trans-interact with other CAMs such as nectin-like molecules (Necls); nectin-1 for example, has been shown to trans-interact with Necl-1. Nectins also interact with various other proteins, including the actin filament (F-actin)-binding protein, afadin. Mutation in the human nectin-1 gene is associated with cleft lip/palate ectodermal dysplasia syndrome (CLPED1). Nectin-1 is a major receptor for herpes simplex virus through interaction with the viral envelope glycoprotein D.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|.
gi 966924971 172 AICIAATGKPVAHIDWEGDL-GEMESTTTSFPNETATIISQYKLFPTRFARGRRITCVVKH 231
Cdd:cd05890   25 ATCTSANGKPPSVVSWDTRLkGEAEFQEIRNPNGTVTVISRYRLVPSREAHQQSLACIVNY 85

First Ig-like domain of Junctional adhesion molecule-1 (JAM1)and similar domains; a member of the V-set of IgSF domains; The members here are composed of the first Ig-like domain of Junctional Adhesion Molecule-1 (JAM1)and similar domains. JAM1 is an immunoglobulin superfamily (IgSF) protein with two Ig-like domains in its extracellular region; it plays a role in the formation of endothelial and epithelial tight junction and acts as a receptor for mammalian reovirus sigma-1. The 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 first Ig-like domain of JAM1 is a member of the V-set Ig domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C'-C" in the other.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971  44 EPHVTAVWGKNVSLKCLIEVNETITQISWEKIHGksSQTVAVHHPQygfSVQGEYQGRVlfknySLNDATITLHNIGFSD 123
Cdd:cd20946    6 QQVVTVVENQEVILSCKTPKKTSSPRVEWKKLQR--DVTFVVFQNN---KIQGDYKGRA-----EILGTNITIKNVTRSD 75

                         90       100
                 ....*....|....*....|....*.
gi 966924971 124 SGKYICKAVTFPLGNAQSSTTVTVLV 149
Cdd:cd20946   76 SGKYRCEVSARSDGQNLGEVTVTLEV 101

Immunoglobulin (Ig)-like domain of human cartilage link protein (LP), and similar domains; The members here are composed of the immunoglobulin (Ig)-like domain similar to that found in human cartilage link protein (LP; also called hyaluronan and proteoglycan link protein). In cartilage, chondroitin-keratan sulfate proteoglycan (CSPG), aggrecan, forms cartilage link protein stabilized aggregates with hyaluronan (HA). These aggregates contribute to the tissue's load bearing properties. Aggregates having other CSPGs substituting for aggrecan may contribute to the structural integrity of many different tissues. Members of the vertebrate HPLN (hyaluronan/HA and proteoglycan binding link) protein family are physically linked adjacent to CSPG genes.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971  47 VTAVWGKNVSLKCLIEVNETI-----TQISWEKIHGKSSQTVAV------HHPQYGfsvqgEYQGRVLFKNYSLNDATIT 115
Cdd:cd05877    7 VFSHRGGNVTLPCRYHYEPELsaprkIRVKWTKLEVDYAKEEDVlvaigtRHKSYG-----SYQGRVFLRRADDLDASLV 81

                         90
                 ....*....|....
gi 966924971 116 LHNIGFSDSGKYIC 129
Cdd:cd05877   82 ITDLRLEDYGRYRC 95

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 966924971 268 VNLKCNADANPPPfKSVWSR------LDGQWPDGLLASDNTLHFvHPLTFNYSGVYICKVTNSLG 326
Cdd:cd00096    1 VTLTCSASGNPPP-TITWYKngkplpPSSRDSRRSELGNGTLTI-SNVTLEDSGTYTCVASNSAG 63

Immunoglobulin variable (IgV)-like domain in complement receptor of the immunoglobulin superfamily (CRIg); The members here are composed of the immunoglobulin variable (IgV) region of the complement receptor of the immunoglobulin superfamily (CRIg). The N-terminal domain of CRIg (also known as Z39Ig and V-set and Ig domain-containing 4 (VSIG4) belongs to the IgV family of immunoglobulin-like domains while the C-terminal domain of CRIg belongs to the IgC family of immunoglobulin-like domains. Like all members of this family, the CRIg domain contains two beta-sheets: one composed of strands A', G, F, C, C' and C", and the other of strands B, E and D. The complement system is an important part of the innate immune system and is required for removal of pathogens from the bloodstream. After exposure to pathogens, the third component of the complement system, C3, is cleaved to C3b which, after recruitment of factor B, initiates formation of the alternative pathway convertases. CRIg, a complement receptor expressed on macrophages, binds to C3b and iC3b mediating phagocytosis of the particles. It is also a potent inhibitor of the alternative pathway convertases and a negative regulator of T cell activation. 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, such as, T-cell receptors, CD2, CD4, CD8, and membrane glycoproteins, such as, 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.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971  40 PIIVEPH-VTAVWGKNVSLKCLIEVNETITQI--SWEKIHGKSSQTVAVHHPQYGFSVQGEYQGRVLFKNYSLNDATITL 116
Cdd:cd16089    1 PILEGPEsITGPWKGSVNLPCTYVPEEGYTQVlvKWLVQRDSDPVTIFLRDSSGDHIQQAKYRGRLEVSKDTPGDVSLQL 80

                         90
                 ....*....|....*...
gi 966924971 117 HNIGFSDSGKYICkAVTF 134
Cdd:cd16089   81 DTLEMDDRGHYTC-QVTW 97

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
                 ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 966924971 268 VNLKCNADANPPPfKSVWSRLDGQWPDGL--LASDNTLHFVHpLTFNYSGVYICKVTNSLGQ 327
Cdd:cd05725   15 AEFQCEVGGDPVP-TVRWRKEDGELPKGRyeILDDHSLKIRK-VTAGDMGSYTCVAENMVGK 74

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 966924971  47 VTAVWGKNVSLKCLIEVNETiTQISWEKihgKSSQTVavhhpqYGFSVQGEYQGRVLFKNYSLNDATITLHNIGFSDSGK 126
Cdd:cd05882    7 ETVAVGGTVTLKCGVKEHDN-SSLQWSN---TAQQTL------YFGEKRALRDNRIQLVKSTPTELIISISNVQLSDEGE 76

                         90
                 ....*....|....*....
gi 966924971 127 YICKAVTFPLGNAQSSTTV 145
Cdd:cd05882   77 YTCSIFTMPVRTAKATVTV 95

Immunoglobulin I-set domain;

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|..
gi 966924971  268 VNLKCNADANPPPfKSVWSRlDGQwpdgLLASDNTLHF----------VHPLTFNYSGVYICKVTNSLGQRS 329
Cdd:pfam07679  18 ARFTCTVTGTPDP-EVSWFK-DGQ----PLRSSDRFKVtyeggtytltISNVQPDDSGKYTCVATNSAGEAE 83

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 966924971  46 HVTAVWGKNVSLKCLIEVNETiTQISWEKihgKSSQTVAVhhpqygfsvqGEYQG----RVLFKNYSLNDATITLHNIGF 121
Cdd:cd05717    5 DVTVVEGETLTLKCQVSLRDD-SSLQWLN---PNGQTIYF----------NDKRAlrdsRYQLLNHSASELSISVSNVTL 70

                         90       100
                 ....*....|....*....|....*.
gi 966924971 122 SDSGKYICKAVTFPLgnAQSSTTVTV 147
Cdd:cd05717   71 SDEGVYTCLHYTDPV--STKKVTVTV 94

Immunoglobulin variable domain (IgV); The members here are composed of the immunoglobulin variable domain (IgV). The IgV family contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology, and are components of immunoglobulin (Ig) and T cell receptors. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. In Ig, each chain is composed of one variable domain (IgV) and one or more constant domains (IgC); these names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. Within the variable domain, there are regions of even more variability called the hypervariable or complementarity-determining regions (CDRs) which are responsible for antigen binding. A predominant feature of most Ig domains is the disulfide bridge connecting 2 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" strands in the other.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971  52 GKNVSLKCLIEVNETITQISWekIHGKSSQtvavhHPQY-------GFSVQGEYQGRVLFKNYSLNDATITLHNIGFSDS 124
Cdd:cd00099   13 GESVTLSCEVSSSFSSTYIYW--YRQKPGQ-----GPEFliylsssKGKTKGGVPGRFSGSRDGTSSFSLTISNLQPEDS 85

                         90       100
                 ....*....|....*....|....*.
gi 966924971 125 GKYICKAVTFPLGNAQ---SSTTVTV 147
Cdd:cd00099   86 GTYYCAVSESGGTDKLtfgSGTRLTV 111

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60
                  ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 966924971  268 VNLKCNADANPPPfkSVWSRLDGQWPDGLLASDNTLHF------VHPLTFNYSGVYICKVTN 323
Cdd:pfam13927  19 VTLTCEATGSPPP--TITWYKNGEPISSGSTRSRSLSGsnstltISNVTRSDAGTYTCVASN 78

Immunoglobulin (Ig)-like domain of myelin oligodendrocyte glycoprotein (MOG); The members here are composed of the immunoglobulin (Ig)-like domain of myelin oligodendrocyte glycoprotein (MOG). MOG, a minor component of the myelin sheath, is an important CNS-specific autoantigen, linked to the pathogenesis of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). It is a transmembrane protein having an extracellular Ig domain. MOG is expressed in the CNS on the outermost lamellae of the myelin sheath, and on the surface of oligodendrocytes, and may participate in the completion, compaction, and/or maintenance of myelin. This group also includes butyrophilin (BTN). BTN is the most abundant protein in bovine milk-fat globule membrane (MFGM).

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 966924971  39 GPiivEPHVTAVWGKNVSLKCLI--EVNETITQISWekIHGKSSQtvAVHHPQYG---FSVQ-GEYQGRVLFKNYSLNDA 112
Cdd:cd05713    5 GP---TEPILALVGEDAELPCHLspKMSAEHMEVRW--FRSQFSP--VVHLYRDGqdqEEEQmPEYRGRTELLKDAIAEG 77

                         90
                 ....*....|....*....
gi 966924971 113 TITL--HNIGFSDSGKYIC 129
Cdd:cd05713   78 SVALriHNVRPSDEGQYTC 96

Fifth immunoglobulin (Ig) domain of contactin; The members here are composed of the fifth 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.

                         10        20        30
                 ....*....|....*....|....*....|....*....
gi 966924971 109 LNDATITLHNIGFSDSGKYICKAVTFpLGNAQSSTTVTV 147
Cdd:cd04969   52 LPDGSLKIKNVTKSDEGKYTCFAVNF-FGKANSTGSLSV 89