Immunoglobulin V-Type;

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1344538310   38 SVTLPCTYNTYVSDREgFIQW-DKLLRSQTERVVTWNFVTKKYiYGNRYENRVRVSNDAELSNASITIDQLTMDDNGTYE 116
Cdd:smart00406   1 SVTLSCKFSGSTFSSY-YVSWvRQPPGKGLEWLGYIGSNGSSY-YQESYKGRFTISKDTSKNDVSLTISNLRVEDTGTYY 78

                   ...
gi 1344538310  117 CSV 119
Cdd:smart00406  79 CAV 81

Immunoglobulin V-Type;

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1344538310   38 SVTLPCTYNTYVSDREgFIQW-DKLLRSQTERVVTWNFVTKKYiYGNRYENRVRVSNDAELSNASITIDQLTMDDNGTYE 116
Cdd:smart00406   1 SVTLSCKFSGSTFSSY-YVSWvRQPPGKGLEWLGYIGSNGSSY-YQESYKGRFTISKDTSKNDVSLTISNLRVEDTGTYY 78

                   ...
gi 1344538310  117 CSV 119
Cdd:smart00406  79 CAV 81

Immunoglobulin Variable (IgV) domain of T cell Immunoglobulin Domain and Mucin Domain 3 (Tim-3), and similar domains; The members here are composed of the immunoglobulin variable (IgV) domain of T cell immunoglobulin domain and mucin domain 3 (Tim-3; also known as Hepatitis A virus cellular receptor 2 (HAVcr-2) and Cluster of Differentiation 366 (CD366)) and similar proteins. TIM-3 is a checkpoint inhibitor in immune responses to tumors, as well as involved in chronic viral infections. Thus, Tim-3 has emerged as one of most promising immune checkpoint targets for cancer immunotherapy. Tim-3 is highly expressed on Th1 lymphocytes and CD11b(+) macrophages and is upregulated on activated T and myeloid cells. TIM-3 regulates macrophage, activation and inhibits Th1 mediated immune responses to promote immunological tolerance. There are three TIM family members in humans (TIM-1, TIM-3, and TIM-4) and eight members in mice (TIM-1 to TIM-8). The IgV domain of human TIM-3 has been shown to bind ligands such as carcinoembryonic antigen cell adhesion molecule 1 (CEACAM1), high mobility group protein B1 (HMGB1)and galectin-9 (GAL9). The binding of GAL9 to TIM-3 can negatively regulate Th1 immune response, enhance immune tolerance and inhibit anti#tumor immunity. Dysregulation of the TIM-3/GAL9 pathway is implicated in numerous chronic autoimmune diseases, such as multiple sclerosis and systemic lupus erythematosus.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1344538310  32 RAARGRSVTLPCTYNTYVSDREGFIQWDK--LLRSQTERVVTWnfvTKKYIYGNRYENRVRVSNDAELSNASITIDQLTM 109
Cdd:cd20982     4 RAEVGHNAYLPCSYTTAAPGNLVPVCWGKgaCPVSYCGNVLLR---TDERDVTYQKSSRYQLKGDFSKGDVSLTIENVTL 80

                          90       100
                  ....*....|....*....|....
gi 1344538310 110 DDNGTYECSVS---LMSDQDVNAK 130
Cdd:cd20982    81 ADSGIYCCRIQipgIMNDEKFNLK 104

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1344538310   31 LRAARGRSVTLPCTYNTYVSDRegfiqwdkllrsqtervVTWNFVTKKYIYgnrYENRVRVSNDAelSNASITIDQLTMD 110
Cdd:smart00410   4 VTVKEGESVTLSCEASGSPPPE-----------------VTWYKQGGKLLA---ESGRFSVSRSG--STSTLTISNVTPE 61

                           90       100
                   ....*....|....*....|....*..
gi 1344538310  111 DNGTYECSVslmSDQDVNAKSRVRLLV 137
Cdd:smart00410  62 DSGTYTCAA---TNSSGSASSGTTLTV 85

First immunoglobulin (Ig) domain of nectin-4, and similar domains; The members here are composed of the first immunoglobulin (Ig) domain of nectin-4 (also known as poliovirus receptor related protein 4 or LNIR receptor). Nectin-4 belongs to the nectin family, which is comprised of four transmembrane glycoproteins (nectins-1 through -4). Nectins are synaptic cell adhesion molecules (CAMs) which participate in adhesion and signaling at various intracellular junctions. Nectins form homophilic cis-dimers, followed by homophilic and heterophilic trans-dimers involved in cell-cell adhesion. For example nectin-4 trans-interacts with nectin-1. Nectin-4 has also been shown to interact with the actin filament-binding protein, afadin. Unlike the other nectins, which are widely expressed in adult tissues, nectin-4 is mainly expressed during embryogenesis, and is not detected in normal adult tissue or in serum. Nectin-4 is re-expressed in breast carcinoma, and patients having metastatic breast cancer have a circulating form of nectin-4 formed from the ectodomain

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1344538310  29 DILRAARGRSVTLPCTYNTYVSDREGFIQWDKL-LRSQTERVVTWNFVTKKYIYGNrYENRVRVSNDAELSNASITIDQL 107
Cdd:cd05888     1 DVVTVVLGQDAKLPCFYRGDSGEQVGQVAWARVdAGEGAQEIALLHSKYGLHVFPA-YEGRVEQPPPPRPADGSVLLRNA 79

                          90       100
                  ....*....|....*....|....*....
gi 1344538310 108 TMDDNGTYECSVSLMSDQDVNAKSRVRLL 136
Cdd:cd05888    80 VQADEGEYECRVSTFPAGNFQAELRLRVL 108

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 1344538310  23 TVETTQDILRAARGRSVTLPCTYNTYVSDREgfIQWDKLLRSQTERVVTWNFVTKKYiygnryENRvrvsndAELSNASI 102
Cdd:cd20946     1 TVPSSQQVVTVVENQEVILSCKTPKKTSSPR--VEWKKLQRDVTFVVFQNNKIQGDY------KGR------AEILGTNI 66

                          90       100       110
                  ....*....|....*....|....*....|....*.
gi 1344538310 103 TIDQLTMDDNGTYECSVSLMSDQDVNAKSRVRLLVL 138
Cdd:cd20946    67 TIKNVTRSDSGKYRCEVSARSDGQNLGEVTVTLEVL 102

Immunoglobulin (Ig)-like domain of protein zero (P0) and similar proteins; The members here are composed of the immunoglobulin (Ig) domain of protein zero (P0), a myelin membrane adhesion molecule. P0 accounts for over 50% of the total protein in peripheral nervous system (PNS) myelin. P0 is a single-pass transmembrane glycoprotein with a highly basic intracellular domain and an extracellular Ig domain. The extracellular domain of P0 (P0-ED) is similar to the Ig variable domain, carrying one acceptor sequence for N-linked glycosylation. P0 plays a role in membrane adhesion in the spiral wraps of the myelin sheath. The intracellular domain is thought to mediate membrane apposition of the cytoplasmic faces and may, through electrostatic interactions, interact directly with lipid headgroups. It is thought that homophilic interactions of the P0 extracellular domain mediate membrane juxtaposition in the extracellular space of PNS myelin. This group also contains the Ig domain of sodium channel subunit beta-2 (SCN2B), and of epithelial V-like antigen 1 (EVA). EVA, also known as myelin protein zero-like 2, is an adhesion molecule, which may play a role in structural organization of the thymus and early lymphocyte development. SCN2B subunits play a role in determining sodium channel density and function in neurons,and in control of electrical excitability in the brain.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1344538310  26 TTQDILRAARGRSVTLPCTYN-TYVSDREGFIQWDKLLRSQTERVVTWNFVTKKYIYGN--RYENRVRVSNDAELSNASI 102
Cdd:cd05715     4 YTPRELNVLNGSDVRLTCTFTsCYTVGDAFSVTWTYQPEGGNTTESMFHYSKGKPYILKvgRFKDRVSWAGNPSKKDASI 83

                          90       100       110
                  ....*....|....*....|....*....|....*
gi 1344538310 103 TIDQLTMDDNGTYECSVSLMSDQDVnAKSRVRLLV 137
Cdd:cd05715    84 VISNLQFSDNGTYTCDVKNPPDIVG-GHGEIRLYV 117

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 1344538310  33 AARGRSVTLPCTYNTYVSDreGFIQWDKLLRSQT-ERVVTWNfvTKKYIYGNRYENRVRVSNDAElSNASITIDQLTMDD 111
Cdd:cd00099    10 VQEGESVTLSCEVSSSFSS--TYIYWYRQKPGQGpEFLIYLS--SSKGKTKGGVPGRFSGSRDGT-SSFSLTISNLQPED 84

                  ....*....
gi 1344538310 112 NGTYECSVS 120
Cdd:cd00099    85 SGTYYCAVS 93

Immunoglobulin (Ig)-like domain of the chondroitin sulfate proteoglycan core protein (CSPG), versican; The members here are composed of the immunoglobulin (Ig)-like domain of the chondroitin sulfate proteoglycan core protein (CSPG), versican. 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. Like aggrecan, versican has a wide distribution in connective tissue and extracellular matrices. 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 1344538310  31 LRAARGRSVTLPCTYNT-------YVSDREGF-IQWDKLLRS-------QTERVVTWNFVTKkyiYGNRYENRVRVSNDA 95
Cdd:cd05901     7 VHGSLSGSVVLPCRFSTlptlppsYNITSEFLrIKWTKIQVDkngkdhkETTVLVAQNGIIK---IGQEYMGRVSVPSHP 83

                          90       100
                  ....*....|....*....|....*
gi 1344538310  96 E-LSNASITIDQLTMDDNGTYECSV 119
Cdd:cd05901    84 EdQGDASLTIVKLRASDAGVYRCEV 108

N-terminal immunoglobulin (Ig)-like domain of T-cell surface antigen CD2, and similar domains; The members here are composed of the N-terminal immunoglobulin (Ig)-like domain (or domain 1) of T-cell surface antigen Clusters of Differentiation (CD) 2 and similar proteins. CD2 is a T-cell specific surface glycoprotein and is critically important for mediating adhesion between T cells and antigen-presenting cells or between cytolytic T cells and target cells. CD2 is located on chromosome 1 at 1p13 in humans and on chromosome 3 in mice. CD2 contains an extracellular domain with two or Ig-like domains, a single transmembrane segment, and a cytoplasmic region rich in proline and basic residues.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1344538310  33 AARGRSVTLPCTYNTYVSDRegfIQWDKllrsQTERVVTWNFVTKKYIYGNrYENRVRVSNdaelSNASITIDQLTMDDN 112
Cdd:cd05775     7 GALGGNVTLTISSLQDDIDE---IKWKK----TKDKIVEWENNIGPTYFGS-FKDRVLLDK----ESGSLTIKNLTKEDS 74

                          90       100
                  ....*....|....*....|....*.
gi 1344538310 113 GTYECSVSlmSDQDVNAKSRVRLLVL 138
Cdd:cd05775    75 GTYELEIT--STNGKVLSSKFTLEVL 98

N-terminal immunoglobulin (Ig)-like domain of the signaling lymphocyte activation molecule (SLAM) family; The members here are composed of the N-terminal immunoglobulin (Ig)-like domain of the signaling lymphocyte activation molecule (SLAM) family and similar proteins. The SLAM family is a group of immune-cell specific receptors that can regulate both adaptive and innate immune responses. Members of this group include proteins such as CD84, SLAM (CD150), Ly-9 (CD229), NTB-A (ly-108, SLAM6), 19A (CRACC), and SLAMF9. The genes coding for the SLAM family are nested on chromosome 1, in humans at 1q23, and in mice at 1H2. The SLAM family is a subset of the CD2 family, which also includes CD2 and CD58 located on chromosome 1 at 1p13 in humans. In mice, CD2 is located on chromosome 3, and there is no CD58 homolog. The SLAM family proteins are organized as an extracellular domain with either two or four Ig-like domains, a single transmembrane segment, and a cytoplasmic region having Tyr-based motifs. The extracellular domain is organized as a membrane-distal Ig variable (IgV) domain that is responsible for ligand recognition and a membrane-proximal truncated Ig constant-2 (IgC2) domain.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1344538310  36 GRSVTLPctYNTYVSDREGFIQWdklLRSQTERVVTWNFVTKKYI--YGNRYENRVRVSNDaelsNASITIDQLTMDDNG 113
Cdd:cd16842     8 GGSVTFP--LNISDGQEIENITW---SFKTSLAVIAPGEGGAPEIiiTDKSYKERLNISQN----DYSLQISNLTMEDAG 78

                          90
                  ....*....|..
gi 1344538310 114 TYECSVSLMSDQ 125
Cdd:cd16842    79 SYRARINTKNSR 90

Immunoglobulin (Ig)-like domain of the aggrecan-like chondroitin sulfate proteoglycan core protein (CSPG); The members here are composed of the immunoglobulin (Ig)-like domain of the aggrecan-like chondroitin sulfate proteoglycan core proteins (CSPGs). Included in this group are the Ig domains of other CSPGs: versican, and neurocan. In CSPGs, this 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, aggrecan forms cartilage link protein stabilized aggregates with hyaluronan (HA). These aggregates contribute to the tissue's load bearing properties. Aggrecan and versican have a wide distribution 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 1344538310  31 LRAARGRSVTLPC----------TYNTYVSDRegfIQWDKLLRSQTERVVTWNFVTKKYIY--GNRYENRVRVSNDAEL- 97
Cdd:cd05878     7 VRVLLGTSVTLPCyfidpphpvtPSTAPLAPR---IKWSKVSVDGKKEKEVVLLVATEGRVrvNSAYQGRVSLPNYPAIp 83

                          90       100
                  ....*....|....*....|..
gi 1344538310  98 SNASITIDQLTMDDNGTYECSV 119
Cdd:cd05878    84 SDATLEVQSLRASDSGLYRCEV 105

Immunoglobulin Variable (IgV) domain of B7-H4; The members here are composed of the immunoglobulin variable (IgV) domain of B7-H4 (also known as B7-S1, B7x, or Vtcn1). B7-H4 is one of the B7 family of immune-regulatory ligands that act as negative regulators of T cell function; it contains one IgV domain and one IgC domain. The B7-family consists of structurally related cell-surface protein ligands, which bind to receptors on lymphocytes that regulate immune responses. The binding of B7-H4 to unidentified receptors results in the inhibition of TCR-mediated T cell proliferation, cell-cycle progression and IL-2 production. As a co-inhibitory molecule, B7-H4 is widely expressed in tumor tissues and its expression is significantly associated with poor prognosis in human cancers such as glioma, pancreatic cancer, oral squamous cell carcinoma, renal cell carcinoma, and lung cancer.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1344538310  31 LRAARGRSVTLPCTYNTYVSDREGFIQWDKLLRSQtervvtwnfVTKKYIYGN--------RYENRVRV-SNDAELSNAS 101
Cdd:cd20984     7 LAGNIGEDGILSCTFTPDIKLSDIVIQWLKEGDSG---------LVHEFKEGKdelsrqspMFRGRTSLfADQVHVGNAS 77

                          90
                  ....*....|....*....
gi 1344538310 102 ITIDQLTMDDNGTYECSVS 120
Cdd:cd20984    78 LRLKNVQLTDAGTYLCIIS 96

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 1344538310  35 RGRSVTLPCTYNTYVSDREGFiQWD-------KLLRSQTERVVTWNFVTKKYiygnryenrvrvsndaelsnASITIDQL 107
Cdd:cd05742    16 QGETLVLNCTANVNLNEVVDF-QWTypsekegKLALLKPDIKVDWSEPGEFV--------------------STLTIPEA 74

                          90       100
                  ....*....|....*....|....
gi 1344538310 108 TMDDNGTYECSVSLMSDQDVNAKS 131
Cdd:cd05742    75 TLKDSGTYTCAARSGVMKKEKQTS 98

Immunoglobulin (Ig)-like domain of the chondroitin sulfate proteoglycan core protein (CSPG), aggrecan; The members here are composed of the immunoglobulin (Ig)-like domain of the chondroitin sulfate proteoglycan core protein (CSPG), aggrecan. 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, aggrecan forms cartilage link protein stabilized aggregates with HA. These aggregates contribute to the tissue's load bearing properties. Aggrecan has a wide distribution in connective tissue and extracellular matrices. 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 1344538310  31 LRAARGRSVTLPCTYNTYVSDREGF---------IQWDKLLRSQTERVVTwnfVTKKYIYGN-RYENRVRVSN-DAELSN 99
Cdd:cd05900     7 LRVVLGSSLLIPCYFQDPIAKDPGAptvaplsprIKWSFISKEKESVLLV---ATEGKVRVNtEYLDRVSLPNyPAIPSD 83

                          90       100
                  ....*....|....*....|
gi 1344538310 100 ASITIDQLTMDDNGTYECSV 119
Cdd:cd05900    84 ATLEITELRSNDSGTYRCEV 103

Immunoglobulin Variable region-containing chitin-binding proteins; an immunoglobulin V-set domain; The members here are composed of the immunoglobulin variable (IgV) region-containing chitin-binding proteins (VCBPs). VCBPs are secreted, immune-type molecules that have been identified in both amphioxus and sea squirt (Ciona intestinalis). VCBPs, which consist of a leader peptide, two tandem N-terminal immunoglobulin V-type domains and a single C-terminal chitin-binding domain, belong to a multigene family encoding secreted proteins. The VCBPs were identified first in the cephalochordate Branchiostoma floridae and show structural similarities with V-type domains of immunoglobulins and T cell receptors, suggesting that VCBPs represent a unique gut-associated form of innate immune proteins. 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. 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, having A, B, E and D strands in one beta-sheet and A', G, F, C, C' and C" in the other.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1344538310  36 GRSVTLPCTYNTYVSDREGFIQWDKLLRSQTERVV-----TWNFVTKKY-IYGNRYENRVRVSNdaeLSNASITIDQLTM 109
Cdd:cd20963    17 GNRVELPCSYTISPAAQPPTITWLKGISVDRAEVVfkgfkYWNETSSSGeVYFGDYAGRASVAS---LTQPTLVLTDLKF 93

                          90       100
                  ....*....|....*....|....*..
gi 1344538310 110 DDNGTYECSVSLMSDQD---VNAKSRV 133
Cdd:cd20963    94 DDWGRYWCRVANWSQRDefgTDAESML 120

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

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1344538310  24 VETTQDILRAARGRSVTLPCTYNTyvSDREGFIQWDKLLRSQtervvTWNFVTKKY-IYGNRYENRVRVSNDAELSNASI 102
Cdd:cd07706     2 VTQAQPDVSVQVGEEVTLNCRYET--SWTNYYLFWYKQLPSG-----EMTFLIRQDsSEQNAKSGRYSVNFQKAQKSISL 74

                          90       100
                  ....*....|....*....|....
gi 1344538310 103 TIDQLTMDDNGTYECSVSLMSDQD 126
Cdd:cd07706    75 TISALQLEDSAKYFCALSLPYDTD 98