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 71152965 256 TVVGVLGEPVTLPLALPACRDTEKVVWLFNTSIISKEREEAaTADPLIKSRDPYKNRVWVSSQDCSLKISQLKIEDAGPY 335
Cdd:cd16842   2 EVNGILGGSVTFPLNISDGQEIENITWSFKTSLAVIAPGEG-GAPEIIITDKSYKERLNISQNDYSLQISNLTMEDAGSY 80

                        90       100
                ....*....|....*....|..
gi 71152965 336 HAYVCSEASSVTSMTHVTLLIY 357
Cdd:cd16842  81 RARINTKNSRVTITKEFTLHIY 102

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 71152965 256 TVVGVLGEPVTLPLALPACRDTEKVVWLFNTSIISKEREEAaTADPLIKSRDPYKNRVWVSSQDCSLKISQLKIEDAGPY 335
Cdd:cd16842   2 EVNGILGGSVTFPLNISDGQEIENITWSFKTSLAVIAPGEG-GAPEIIITDKSYKERLNISQNDYSLQISNLTMEDAGSY 80

                        90       100
                ....*....|....*....|..
gi 71152965 336 HAYVCSEASSVTSMTHVTLLIY 357
Cdd:cd16842  81 RARINTKNSRVTITKEFTLHIY 102

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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 71152965 174 ITLMCSVKGAEKSVLYSWT----PREPHASESNGGSILTVSRTPCDPDLPYICTAQNPVSQRSSLPV 236
Cdd:cd05740  18 VTLTCEPETQNTSYLWWFNgqslPVTPRLTLSNGNRTLTLLNVTREDAGAYQCEISNPVSANRSDPV 84

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 71152965 256 TVVGVLGEPVTLPLALPACRDTEKVVWLFNTSIISKEREEAaTADPLIKSRDPYKNRVWVSSQDCSLKISQLKIEDAGPY 335
Cdd:cd16842   2 EVNGILGGSVTFPLNISDGQEIENITWSFKTSLAVIAPGEG-GAPEIIITDKSYKERLNISQNDYSLQISNLTMEDAGSY 80

                        90       100
                ....*....|....*....|..
gi 71152965 336 HAYVCSEASSVTSMTHVTLLIY 357
Cdd:cd16842  81 RARINTKNSRVTITKEFTLHIY 102

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 71152965 255 ETVVGVLGEPVTL-PLALPACRDteKVVWLFNtsiiskeREEAATADPLIKSR--DPYKNRVWVSSQDCSLKISQLKIED 331
Cdd:cd05775   3 GEVYGALGGNVTLtISSLQDDID--EIKWKKT-------KDKIVEWENNIGPTyfGSFKDRVLLDKESGSLTIKNLTKED 73

                        90       100
                ....*....|....*....|....*.
gi 71152965 332 AGPYHAYVCSEASSVTSMTHvTLLIY 357
Cdd:cd05775  74 SGTYELEITSTNGKVLSSKF-TLEVL 98

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 71152965  51 APTVVSGILGGSVTLPLNISVD---TEIENVIWIGPKNA--LAFARPKENVTI----MVKSYLGRLDITKWSYSLCISNL 121
Cdd:cd20989   5 VPPEVRGFLGGSVTLPCHLLPPnmvTHVSQVTWQRHDEHgsVAVFHPKQGPSFpeseRLSFVAARLGAELRNASLAMFGL 84

                        90
                ....*....|..
gi 71152965 122 TLNDAGSYKAQI 133
Cdd:cd20989  85 RVEDEGNYTCEF 96