Immunoglobulin Variable (IgV) domain at the N-terminus of CD33 and related Siglecs (sialic acid-binding Ig-like lectins); The members here are composed of the immunoglobulin (Ig) domain at the N-terminus of Cluster of Differentiation (CD) 33 and related Siglecs (sialic acid-binding Ig-like lectins). Siglec refers to a structurally related protein family that specifically recognizes sialic acid in oligosaccharide chains of glycoproteins and glycolipids. Siglecs are type I transmembrane proteins, organized as an extracellular module composed of Ig-like domains, an N-terminal variable set of Ig-like carbohydrate recognition domains, and 1 to 16 constant Ig-like domains, followed by transmembrane and short cytoplasmic domains. Human Siglecs are classified into two subgroups, one subgroup is comprised of sialoadhesin (Siglec-1), CD22 (Siglec-2), and MAG, the other subgroup is comprised of CD33-related Siglecs which include CD33 (Siglec-3) and human Siglecs 5-11.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 158081784  21 YELQVQKSVTVQEGLCVLVPCSFSYPWNSWySPSPLYVYWFRDGESQYYAEAVATNNPDRRVKPETQGRFRLLGDVRNKN 100
Cdd:cd05712    1 WGLQMPKSVTVQEGLCVLIPCSFSYPADYW-VSNPVHGYWYRGGPYPKYRPPVATNNRTREVHESTQGRFRLLGDPGKKN 79

                         90       100       110       120
                 ....*....|....*....|....*....|....*....|
gi 158081784 101 CSLSIGDARMGDTGNYYFRVERGRNVKYNYVQNKLNLEVT 140
Cdd:cd05712   80 CSLSISDARPEDSGKYFFRVERGDSNKYSYLSNQLSLTVT 119

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
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 158081784 254 TSTLLVLEGEALRLLCEAPSNPPAHLSWFQassapNTTPIANTGILELPRVEFTKEGVFTCRAQHPLGSLHIFLNLSV 331
Cdd:cd20948    2 PSDTYYLSGENLNLSCHAASNPPAQYSWTI-----NGTFQTSSQELFLPAITENNEGTYTCSAHNSLTGKNISLVLSV 74

Immunoglobulin Variable (IgV) domain at the N-terminus of CD33 and related Siglecs (sialic acid-binding Ig-like lectins); The members here are composed of the immunoglobulin (Ig) domain at the N-terminus of Cluster of Differentiation (CD) 33 and related Siglecs (sialic acid-binding Ig-like lectins). Siglec refers to a structurally related protein family that specifically recognizes sialic acid in oligosaccharide chains of glycoproteins and glycolipids. Siglecs are type I transmembrane proteins, organized as an extracellular module composed of Ig-like domains, an N-terminal variable set of Ig-like carbohydrate recognition domains, and 1 to 16 constant Ig-like domains, followed by transmembrane and short cytoplasmic domains. Human Siglecs are classified into two subgroups, one subgroup is comprised of sialoadhesin (Siglec-1), CD22 (Siglec-2), and MAG, the other subgroup is comprised of CD33-related Siglecs which include CD33 (Siglec-3) and human Siglecs 5-11.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 158081784  21 YELQVQKSVTVQEGLCVLVPCSFSYPWNSWySPSPLYVYWFRDGESQYYAEAVATNNPDRRVKPETQGRFRLLGDVRNKN 100
Cdd:cd05712    1 WGLQMPKSVTVQEGLCVLIPCSFSYPADYW-VSNPVHGYWYRGGPYPKYRPPVATNNRTREVHESTQGRFRLLGDPGKKN 79

                         90       100       110       120
                 ....*....|....*....|....*....|....*....|
gi 158081784 101 CSLSIGDARMGDTGNYYFRVERGRNVKYNYVQNKLNLEVT 140
Cdd:cd05712   80 CSLSISDARPEDSGKYFFRVERGDSNKYSYLSNQLSLTVT 119

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 158081784   24 QVQKSVTVQEGLCVLVPCSFSypwnSWYSPSPLYVYWFR--DGESQYYAEAVATNNpdrRVKPETQGRFRLLGDVRNKNC 101
Cdd:pfam07686   1 QTPREVTVALGGSVTLPCTYS----SSMSEASTSVYWYRqpPGKGPTFLIAYYSNG---SEEGVKKGRFSGRGDPSNGDG 73

                          90       100       110
                  ....*....|....*....|....*....|....*....
gi 158081784  102 SLSIGDARMGDTGNYYFRVergRNVKYNYVQNKLNLEVT 140
Cdd:pfam07686  74 SLTIQNLTLSDSGTYTCAV---IPSGEGVFGKGTRLTVL 109

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 158081784   255 STLLVLEGEALRLLCEAPSNPPAHLSWFQassaPNTTPIA-----------NTGILELPRVEFTKEGVFTCRAQHPLGSL 323
Cdd:smart00410   2 PSVTVKEGESVTLSCEASGSPPPEVTWYK----QGGKLLAesgrfsvsrsgSTSTLTISNVTPEDSGTYTCAATNSSGSA 77

                   ....*...
gi 158081784   324 HIFLNLSV 331
Cdd:smart00410  78 SSGTTLTV 85

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 158081784    26 QKSVTVQEGLCVLVPCSFSypwnswySPSPLYVYWFRDGesqyyaeavatnnpdrRVKPETQGRFRLLGDvrNKNCSLSI 105
Cdd:smart00410   1 PPSVTVKEGESVTLSCEAS-------GSPPPEVTWYKQG----------------GKLLAESGRFSVSRS--GSTSTLTI 55

                           90       100
                   ....*....|....*....|....*..
gi 158081784   106 GDARMGDTGNYYFRVERGRNVKYNYVQ 132
Cdd:smart00410  56 SNVTPEDSGTYTCAATNSSGSASSGTT 82

Fifth immunoglobulin (Ig)-like domain of Kirrel (kin of irregular chiasm-like) 3, and similar domains; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the fifth immunoglobulin (Ig)-like domain of Kirrel (kin of irregular chiasm-like) 3 (also known as Neph2). This protein has five Ig-like domains, one transmembrane domain, and a cytoplasmic tail. Included in this group is mammalian Kirrel (also known as Neph1), Kirrel2 (also known as Neph3), and Drosophila RST (also known as irregular chiasm C-roughest) protein. These proteins contain multiple Ig domains, have properties of cell adhesion molecules, and are important in organ development.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*.
gi 158081784 353 CSFRAWPAP-SLCWWLGEKPLEgNSSQGSFKVNSSSAGPWANSSLILHGGLTSVLKVS--CKGWNTYGSQSGSVVL 425
Cdd:cd05758   23 CLVFSSPPPdRIVWSWDEGFLE-SGSSGRFSVETFPTEPGVISVLHISGTQRSDFQTSfnCSAWNRFGEGTAIVSL 97

Immunoglobulin Variable (IgV) domain at the N-terminus of CD33 and related Siglecs (sialic acid-binding Ig-like lectins); The members here are composed of the immunoglobulin (Ig) domain at the N-terminus of Cluster of Differentiation (CD) 33 and related Siglecs (sialic acid-binding Ig-like lectins). Siglec refers to a structurally related protein family that specifically recognizes sialic acid in oligosaccharide chains of glycoproteins and glycolipids. Siglecs are type I transmembrane proteins, organized as an extracellular module composed of Ig-like domains, an N-terminal variable set of Ig-like carbohydrate recognition domains, and 1 to 16 constant Ig-like domains, followed by transmembrane and short cytoplasmic domains. Human Siglecs are classified into two subgroups, one subgroup is comprised of sialoadhesin (Siglec-1), CD22 (Siglec-2), and MAG, the other subgroup is comprised of CD33-related Siglecs which include CD33 (Siglec-3) and human Siglecs 5-11.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 158081784  21 YELQVQKSVTVQEGLCVLVPCSFSYPWNSWySPSPLYVYWFRDGESQYYAEAVATNNPDRRVKPETQGRFRLLGDVRNKN 100
Cdd:cd05712    1 WGLQMPKSVTVQEGLCVLIPCSFSYPADYW-VSNPVHGYWYRGGPYPKYRPPVATNNRTREVHESTQGRFRLLGDPGKKN 79

                         90       100       110       120
                 ....*....|....*....|....*....|....*....|
gi 158081784 101 CSLSIGDARMGDTGNYYFRVERGRNVKYNYVQNKLNLEVT 140
Cdd:cd05712   80 CSLSISDARPEDSGKYFFRVERGDSNKYSYLSNQLSLTVT 119

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 158081784   24 QVQKSVTVQEGLCVLVPCSFSypwnSWYSPSPLYVYWFR--DGESQYYAEAVATNNpdrRVKPETQGRFRLLGDVRNKNC 101
Cdd:pfam07686   1 QTPREVTVALGGSVTLPCTYS----SSMSEASTSVYWYRqpPGKGPTFLIAYYSNG---SEEGVKKGRFSGRGDPSNGDG 73

                          90       100       110
                  ....*....|....*....|....*....|....*....
gi 158081784  102 SLSIGDARMGDTGNYYFRVergRNVKYNYVQNKLNLEVT 140
Cdd:pfam07686  74 SLTIQNLTLSDSGTYTCAV---IPSGEGVFGKGTRLTVL 109

Second immunoglobulin domain of Cluster of Differentiation (CD) 22; member of the Constant 1 (C1)-set of IgSF domains; The members here are composed of the second immunoglobulin domain of clusters of differentiation (CD) 22 (also known as Siglec-2). CD22, a sialic-acid binding immunoglobulin type-lectin (Siglec) family member, is an inhibitory co-receptor of the B-cell receptor (BCR). The inhibitory function of CD22 and its restricted expression on B cells makes CD22 an attractive target against dysregulated B cells that cause autoimmune diseases and B-cell-derived cancers. CD22 plays a vital role in establishing a baseline level of B-cell inhibition, and thus is an important determinant of homeostasis in humoral immunity. Siglecs are primarily expressed on immune cells and recognize sialic acid-containing glycan ligands. Siglecs are organized as an extracellular module composed of Ig-like domains (an N-terminal variable set of Ig-like carbohydrate recognition domains, and 1 to 16 constant Ig-like domains), followed by transmembrane and short cytoplasmic domains. Human Siglecs are classified into two subgroups, one subgroup is comprised of sialoadhesin (Siglec-1), CD22 (Siglec-2), and MAG (Siglec-4, myelin-associated glycoprotein), the other subgroup is comprised of CD33-related Siglecs which include CD33 (Siglec-3) and human Siglecs 5-11. 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 C1-set of IgSF domains.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 158081784 152 EPLESGRLTrLSCSLPGSCeVGRPLTFSWTGD----------VLSPLDPETTGSSELTLTPRPEDHGTNLTCHVKHQGAQ 221
Cdd:cd20938   10 EIQESQEVT-LTCLLNFSC-YGYPIQLQWLLEgspmrqaavtSTSLTIKSVFTRSELKFQPKWSHHGKIVTCQLQDADGK 87

                         90
                 ....*....|.
gi 158081784 222 VTTERTVQLNV 232
Cdd:cd20938   88 VLSEDTVQLNV 98

First immunoglobulin domain of Cluster of Differentiation (CD) 22; member of the V-set of IgSF domains; The members here are composed of the first immunoglobulin domain in Cluster of Differentiation (CD) 22 (also known as Siglec-2). CD22, a sialic-acid binding immunoglobulin type-lectin (Siglec) family member, is an inhibitory co-receptor of the B-cell receptor (BCR). The inhibitory function of CD22 and its restricted expression on B cells makes CD22 an attractive target against dysregulated B cells that cause autoimmune diseases and B-cell-derived cancers. CD22 plays a vital role in establishing a baseline level of B-cell inhibition, and thus is an important determinant of homeostasis in humoral immunity. Siglecs are primarily expressed on immune cells and recognize sialic acid-containing glycan ligands. Siglecs are organized as an extracellular module composed of Ig-like domains (an N-terminal variable set of Ig-like carbohydrate recognition domains, and 1 to 16 constant Ig-like domains), followed by transmembrane and short cytoplasmic domains. Human Siglecs are classified into two subgroups, one subgroup is comprised of sialoadhesin (Siglec-1), CD22 (Siglec-2), and MAG (Siglec-4, myelin-associated glycoprotein), the other subgroup is comprised of CD33-related Siglecs which include CD33 (Siglec-3) and human Siglecs 5-11. 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 V-set of IgSF domains.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 158081784  33 EGLCVLVPCSFSYPWNSWYSPSPLYVYWFRDGESQYYAEAVATNNPDRRVKPEtQGRFRLLGDvRNKNCSLSIGDARMGD 112
Cdd:cd20929   13 EGACVWIPCTYRALDGDLESFILFHNPEYNKATSKFDGTRLYESTKDGKVPSE-QKRVQFLGD-KNKNCTLSIHPVHLND 90

                         90
                 ....*....|.
gi 158081784 113 TGNYYFRVERG 123
Cdd:cd20929   91 SGQLGLRMESK 101

Immunoglobulin (Ig)-like domain of the chondroitin sulfate proteoglycan core protein (CSPG), neurocan; The members here are composed of the immunoglobulin (Ig)-like domain of the chondroitin sulfate proteoglycan core protein (CSPG), neurocan. In CSPGs, the Ig-like domain is followed by hyaluronan (HA)-binding tandem repeats, and a C-terminal region with epidermal growth factor-like, lectin-like, and complement regulatory protein-like domains. Separating these N- and C-terminal regions is a nonhomologous glycosaminoglycan attachment region. In cartilage, the CSPG aggrecan (not included in this group) forms cartilage link protein stabilized aggregates with HA. These aggregates contribute to the tissue's load bearing properties. Unlike aggrecan which is widely distributed in connective tissue and extracellular matrices, neurocan is localized almost exclusively in nervous tissue. 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 158081784  31 VQEGLC--VLVPCSFSYPWNSWYSPSPLYVYWFR---DGESQYYAEAVATNNPdRRVKPETQGRFRLLGDVRNK-NCSLS 104
Cdd:cd05902    7 VRRPLSssVLLPCVFTLPPSASSPPEGPRIKWTKlstSGGQQQRPVLVARDNV-VRVAKAFQGRVSLPGYPKNRyNASLV 85

                         90       100       110
                 ....*....|....*....|....*....|....*...
gi 158081784 105 IGDARMGDTGNYYFRVERGrnvkYNYVQNKLNLEVTAL 142
Cdd:cd05902   86 LSRLRYSDSGTYRCEVVLG----INDEQDTVPLEVTGV 119

Immunoglobulin (Ig) variable (V) domain of T-cell receptor (TCR) gamma chain; The members here are composed of the immunoglobulin (Ig) variable (V) domain of the gamma chain of gamma/delta T-cell receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes, and are heterodimers consisting of alpha and beta chains or gamma and delta chains. Each chain contains a variable (V) and a constant (C) region. The majority of T cells contain alpha/beta TCRs, but a small subset contain gamma/delta TCRs. Alpha/beta TCRs recognize antigens as peptide fragments presented by major histocompatibility complex (MHC) molecules. Gamma/delta TCRs recognize intact protein antigens directly without antigen processing and recognize MHC independently of the bound peptide. Gamma/delta T cells can also be stimulated by non-peptide antigens such as small phosphate- or amine-containing compounds. The variable domain of gamma/delta TCRs is responsible for antigen recognition and is located at the N-terminus of the receptor. Members of this group contain the standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 158081784  24 QVQKSVTVQEGLCVLVPCSFSYPWNSwyspsPLYVYWFR--DGESQYYAEAVATNNPDRRVKPETQGRFRLLGDVRNKNC 101
Cdd:cd04982    3 QPQLSITREESKSVTISCKVSGIDFS-----TTYIHWYRqkPGQALERLLYVSSTSAVRKDSGKTKNKFEARKDVGKSTS 77

                         90
                 ....*....|....*.
gi 158081784 102 SLSIGDARMGDTGNYY 117
Cdd:cd04982   78 TLTITNLEKEDSATYY 93

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
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 158081784  254 TSTLLVLEGEALRLLCEA-PSNPPAHLSWFQASSAPNT---TPIANTGI----LELPRVEFTKEGVFTCRAQHPLGS 322
Cdd:pfam00047   3 PPTVTVLEGDSATLTCSAsTGSPGPDVTWSKEGGTLIEslkVKHDNGRTtqssLLISNVTKEDAGTYTCVVNNPGGS 79

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 158081784 265 LRLLCEAPSNPPAHLSWF------QASSAPNTTPIANTGILELPRVEFTKEGVFTCRAQHPLG 321
Cdd:cd00096    1 VTLTCSASGNPPPTITWYkngkplPPSSRDSRRSELGNGTLTISNVTLEDSGTYTCVASNSAG 63

Immunoglobulin domain; This domain contains immunoglobulin-like domains.

                          10        20        30        40        50        60
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 158081784  255 STLLVLEGEALRLLCEAPSNPPAHLSWFQassapNTTPIANTGILELPRVEFTKEGVFTCRAQHPLGS 322
Cdd:pfam13895   7 SPTVVTEGEPVTLTCSAPGNPPPSYTWYK-----DGSAISSSPNFFTLSVSAEDSGTYTCVARNGRGG 69

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 158081784  24 QVQKSVTVQEGLCVLVPCSFSYpwnswySPSPLYVYWFRDGESQYYAEAVATNNPDRRVKPETQGRFRLLGDvRNKNCSL 103
Cdd:cd00099    3 QSPRSLSVQEGESVTLSCEVSS------SFSSTYIYWYRQKPGQGPEFLIYLSSSKGKTKGGVPGRFSGSRD-GTSSFSL 75

                         90
                 ....*....|....
gi 158081784 104 SIGDARMGDTGNYY 117
Cdd:cd00099   76 TISNLQPEDSGTYY 89

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

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 158081784 174 RPLTFSWTGD-VLSPLDPETTG-----------SSELTLTPRPEDHGTNLTCHVKHQGAQVTTERTV 228
Cdd:cd00098   29 KDITVTWLKNgVPLTSGVSTSSpvepndgtysvTSSLTVPPSDWDEGATYTCVVTHESLKSPLSKTW 95

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 158081784 173 GRP-LTFSWTGD---------VLSPLDPETTGSSELTLTPRPEDHGTNLTCHVKHQGAQVTTERTVQLNV 232
Cdd:cd07703   27 GRPpARISWSSTlngnanttqVPGPDSGTVTVTSEYSLVPTPEANGKEVTCKVEHETLEEPQLLPVTLSV 96

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 158081784 256 TLLVLEGEALRLLCEAPSNPPAHLSWFQASSAPNTTPIANT--GILELPRVEFTKEGVFTCRAQHPLG 321
Cdd:cd04968   10 DTYALKGQTVTLECFALGNPVPQIKWRKVDGSPSSQWEITTsePVLEIPNVQFEDEGTYECEAENSRG 77