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 9055238   27 VEVPSETEAVQGNPMKLRCI--SCmkrEEVEATTVVEWFYRPEGGKDFL-IYEYRNG--HQEVESPFQGRLQWNGSKDLQ 101
Cdd:cd05715   3 VYTPRELNVLNGSDVRLTCTftSC---YTVGDAFSVTWTYQPEGGNTTEsMFHYSKGkpYILKVGRFKDRVSWAGNPSKK 79

                        90       100
                ....*....|....*....|.
gi 9055238  102 DVSITVLNVTLNDSGLYTCNV 122
Cdd:cd05715  80 DASIVISNLQFSDNGTYTCDV 100

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 9055238   27 VEVPSETEAVQGNPMKLRCI--SCmkrEEVEATTVVEWFYRPEGGKDFL-IYEYRNG--HQEVESPFQGRLQWNGSKDLQ 101
Cdd:cd05715   3 VYTPRELNVLNGSDVRLTCTftSC---YTVGDAFSVTWTYQPEGGNTTEsMFHYSKGkpYILKVGRFKDRVSWAGNPSKK 79

                        90       100
                ....*....|....*....|.
gi 9055238  102 DVSITVLNVTLNDSGLYTCNV 122
Cdd:cd05715  80 DASIVISNLQFSDNGTYTCDV 100

Immunoglobulin (Ig)-like domain of epithelial V-like antigen (EVA) 1; The members here are composed of the immunoglobulin (Ig) domain of epithelial V-like antigen 1 (EVA 1). EVA is also known as myelin protein zero-like 2. EVA is an adhesion molecule and may play a role in the structural organization of the thymus and early lymphocyte development.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 9055238   27 VEVPSETEAVQGNPMKLRCiSCMKREEVEATTVVEWFYRPE--GGKDFLIYEYRNGHQEVESPFQGRLQWNGSKDLQDVS 104
Cdd:cd05880   3 VYTSKEVEAVNGTDVRLKC-TFSSSAPIGDTLVITWNFRPLdgGREESVFYYHKRPYPPPDGRFKGRVVWDGNIMRRDAS 81

                        90
                ....*....|....*...
gi 9055238  105 ITVLNVTLNDSGLYTCNV 122
Cdd:cd05880  82 ILIWQLQPTDNGTYTCQV 99

Immunoglobulin Variable (V) domain of the Coxsackievirus and Adenovirus Receptor (CAR), and similar proteins; The members here are composed of the Variable (V) domain of the Coxsackievirus and Adenovirus Receptor (CAR), and similar proteins. CAR, which is encoded by human CXADR gene, is a cell adhesion molecule of the Immunoglobulin (Ig) superfamily. The CAR acts as a type I membrane receptor for group B1-B6 coxsackie viruses and subgroup C adenoviruses. For instance, adenovirus interacts with the coxsackievirus and adenovirus receptor to enter epithelial airway cells. The CAR is also shown to be involved in physiological processes such as neuronal and heart development, epithelial tight junction integrity, and tumor suppression. The CAR is a component of the epithelial apical junction complex that may function as a homophilic cell adhesion molecule and is essential for tight junction integrity. The CAR is also involved in transepithelial migration of leukocytes through adhesive interactions with JAML a transmembrane protein of the plasma membrane of leukocytes. The interaction between both receptors also mediates the activation of gamma-delta T-cells, a subpopulation of T-cells residing in epithelia and involved in tissue homeostasis and repair. The CAR is composed of one V-set and one C2-set Ig module, a single transmembrane helix, and an intracellular domain. 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 9055238   31 SETEAVQGNPMKLRCISCMKREEVEaTTVVEWFYRPEGGKDFLIYEYRNGH--QEVESPFQGRLQWNGSKDLQDVSITVL 108
Cdd:cd20960   8 TEIKKVAGENVTLPCHHQLGLEDQG-TLDIEWLLLPSDKVEKVVITYSGDRvyNHYYPALKGRVAFTSNDLSGDASLNIS 86

                        90
                ....*....|....
gi 9055238  109 NVTLNDSGLYTCNV 122
Cdd:cd20960  87 NLKLSDTGTYQCKV 100

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 9055238     24 PVCVEVPSETEAVQGNPMKLRCiscmkreEVEA--TTVVEWfyrpeggkdfliyeYRNGHQEVESPFQGRLQWNGSkdlq 101
Cdd:pfam13927   2 PVITVSPSSVTVREGETVTLTC-------EATGspPPTITW--------------YKNGEPISSGSTRSRSLSGSN---- 56

                          90       100
                  ....*....|....*....|..
gi 9055238    102 dVSITVLNVTLNDSGLYTCNVS 123
Cdd:pfam13927  57 -STLTISNVTRSDAGTYTCVAS 77

Immunoglobulin (Ig) variable (V) domain of T-cell receptor (TCR) beta chain; The members here are composed of the immunoglobulin (Ig) variable domain of the beta chain of alpha/beta T-cell antigen receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes, and are composed of alpha and beta, or gamma and delta, polypeptide chains with variable (V) and constant (C) regions. This group includes the variable domain of the alpha chain of alpha/beta TCRs. Alpha/beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. The variable domain of TCRs is responsible for antigen recognition, and is located at the N-terminus of the receptor. Gamma/delta TCRs recognize intact protein antigens directly without antigen processing and recognize MHC independently of the bound peptide. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 9055238   30 PSETEAVQGNPMKLRCISCMKREEVeattvveWFYR--PEGGKDFLIYEYRNGHQEVESPFQGRLQWNGsKDLQDVSITV 107
Cdd:cd05899   5 PRYLIKRRGQSVTLRCSQKSGHDNM-------YWYRqdPGKGLQLLFYSYGGGLNEEGDLPGDRFSASR-PSLTRSSLTI 76

                        90
                ....*....|....*..
gi 9055238  108 LNVTLNDSGLYTCNVSR 124
Cdd:cd05899  77 KSAEPEDSAVYLCASSL 93

Immunoglobulin (Ig) variable (V) domain of T-cell receptor (TCR) alpha chain and similar proteins; The members here are composed of the immunoglobulin (Ig) variable domain of the alpha chain of alpha/beta T-cell antigen receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes, and are composed of alpha and beta, or gamma and delta polypeptide chains with variable (V) and constant (C) regions. This group represents the variable domain of the alpha chain of TCRs and also includes the variable domain of delta chains of TCRs. Alpha/beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. The variable domain of TCRs is responsible for antigen recognition, and is located at the N-terminus of the receptor. Gamma/delta TCRs recognize intact protein antigens directly without antigen processing and recognize MHC independently of the bound peptide. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 9055238   30 PSETEAVQGNPMKLRCiscmkREEVEATTVVEWfYR--PEGGKDFLIYEYRNGhQEVESpfqGRLQWNGSKDLQDVSITV 107
Cdd:cd04983   5 PQSLSVQEGENVTLNC-----NYSTSTFYYLFW-YRqyPGQGPQFLIYISSDS-GNKKK---GRFSATLDKSRKSSSLHI 74

                        90
                ....*....|....*.
gi 9055238  108 LNVTLNDSGLYTCNVS 123
Cdd:cd04983  75 SAAQLSDSAVYFCALS 90

First immunoglobulin variable (IgV) domain of poliovirus receptor (PVR, also known as CD155 and necl-5), and similar domains; The members here are composed of the first immunoglobulin (Ig) domain of poliovirus receptor (PVR, also known as CD155 and nectin-like protein 5 (necl-5)). 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), that result from alternate splicing of the CD155 mRNA, and have identical extracellular domains. CD155-beta and CD155-gamma are secreted; 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" with a footprint similar to that of the intercellular adhesion molecule-1 receptor on human rhinoviruses. This group also includes the first Ig-like domain of nectin-1 (also known as poliovirus receptor related protein(PVRL)1; CD111), nectin-3 (also known as PVRL 3), nectin-4 (also known as PVRL4; LNIR receptor)and DNAX accessory molecule 1 (DNAM-1; CD226).

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 9055238   27 VEVPSETEAVQGNPMKLRCIscMKREEVEATTVVEWFyRPEGGKDFLIYEYrngHQE----VESPFQGRLQW-NGSKDLQ 101
Cdd:cd05718   3 VQVPTEVTGFLGGSVTLPCS--LTSPGTTKITQVTWM-KIGAGSSQNVAVF---HPQygpsVPNPYAERVEFlAARLGLR 76

                        90
                ....*....|....*....
gi 9055238  102 DVSITVLNVTLNDSGLYTC 120
Cdd:cd05718  77 NATLRIRNLRVEDEGNYIC 95

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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 9055238   57 TTVVEWfYR--PEGGKDFLIYEYrNGHQEVESPFQGRLQWNGSKDlQDVSITVLNVTLNDSGLYTCNVSR 124
Cdd:cd00099  28 STYIYW-YRqkPGQGPEFLIYLS-SSKGKTKGGVPGRFSGSRDGT-SSFSLTISNLQPEDSGTYYCAVSE 94