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 1104325227  23 LTQPRSVSGSPGQSVTISCTGTSSDVGGYnYVSWYQQHPGKAPKLMIYDVSKRPSGVPDRFSGSKSGNTASLTISGLQAE 102
Cdd:cd04984     2 LTQPSSLSVSPGETVTITCTGSSGNISGN-YVNWYQQKPGSAPRYLIYEDKHRPSGIPDRFSGSKSGNTASLTISGAQTE 80

                          90
                  ....*....|....*..
gi 1104325227 103 DEADYYCCS-YAGSYTF 118
Cdd:cd04984    81 DEADYYCQVwDSNSYVF 97

Immunoglobulin (Ig) lambda light chain variable (V) domain; The members here are composed of the immunoglobulin (Ig) light chain, lambda type, variable (V) domain. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. There are two types of light chains: kappa and lambda, each composed of a constant domain (CL) and a variable domain (VL). There are five types of heavy chains (alpha, gamma, delta, epsilon, and mu), which determines the type of immunoglobulin formed: IgA, IgG, IgD, IgE, and IgM, respectively. In higher vertebrates, there are two types of light chain, designated kappa and lambda, which seem to be functionally identical, and can associate with any of the heavy chains. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1104325227  23 LTQPRSVSGSPGQSVTISCTGTSSDVGGYnYVSWYQQHPGKAPKLMIYDVSKRPSGVPDRFSGSKSGNTASLTISGLQAE 102
Cdd:cd04984     2 LTQPSSLSVSPGETVTITCTGSSGNISGN-YVNWYQQKPGSAPRYLIYEDKHRPSGIPDRFSGSKSGNTASLTISGAQTE 80

                          90
                  ....*....|....*..
gi 1104325227 103 DEADYYCCS-YAGSYTF 118
Cdd:cd04984    81 DEADYYCQVwDSNSYVF 97

Immunoglobulin V-Type;

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1104325227   36 SVTISCTGTSSDVGGYnYVSWYQQHPGKAPKLMIYDVSKR----PSGVPDRFSGSK--SGNTASLTISGLQAEDEADYYC 109
Cdd:smart00406   1 SVTLSCKFSGSTFSSY-YVSWVRQPPGKGLEWLGYIGSNGssyyQESYKGRFTISKdtSKNDVSLTISNLRVEDTGTYYC 79

Immunoglobulin (Ig) lambda light chain variable (V) domain; The members here are composed of the immunoglobulin (Ig) light chain, lambda type, variable (V) domain. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. There are two types of light chains: kappa and lambda, each composed of a constant domain (CL) and a variable domain (VL). There are five types of heavy chains (alpha, gamma, delta, epsilon, and mu), which determines the type of immunoglobulin formed: IgA, IgG, IgD, IgE, and IgM, respectively. In higher vertebrates, there are two types of light chain, designated kappa and lambda, which seem to be functionally identical, and can associate with any of the heavy chains. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1104325227  23 LTQPRSVSGSPGQSVTISCTGTSSDVGGYnYVSWYQQHPGKAPKLMIYDVSKRPSGVPDRFSGSKSGNTASLTISGLQAE 102
Cdd:cd04984     2 LTQPSSLSVSPGETVTITCTGSSGNISGN-YVNWYQQKPGSAPRYLIYEDKHRPSGIPDRFSGSKSGNTASLTISGAQTE 80

                          90
                  ....*....|....*..
gi 1104325227 103 DEADYYCCS-YAGSYTF 118
Cdd:cd04984    81 DEADYYCQVwDSNSYVF 97

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 1104325227  23 LTQ-PRSVSGSPGQSVTISCTGTSSDvgGYNYVSWYQQHPGKAPKLMIY---DVSKRPSGVPDRFSGSKSG-NTASLTIS 97
Cdd:cd00099     1 VTQsPRSLSVQEGESVTLSCEVSSSF--SSTYIYWYRQKPGQGPEFLIYlssSKGKTKGGVPGRFSGSRDGtSSFSLTIS 78

                          90       100
                  ....*....|....*....|..
gi 1104325227  98 GLQAEDEADYYCCSYAGSYTFH 119
Cdd:cd00099    79 NLQPEDSGTYYCAVSESGGTDK 100

Immunoglobulin V-Type;

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1104325227   36 SVTISCTGTSSDVGGYnYVSWYQQHPGKAPKLMIYDVSKR----PSGVPDRFSGSK--SGNTASLTISGLQAEDEADYYC 109
Cdd:smart00406   1 SVTLSCKFSGSTFSSY-YVSWVRQPPGKGLEWLGYIGSNGssyyQESYKGRFTISKdtSKNDVSLTISNLRVEDTGTYYC 79

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1104325227   26 PRSVSGSPGQSVTISCTGTSSDVggyNYVSWYQQHPgkapklmiydvskRPSGVPDRFSGSKSGNTASLTISGLQAEDEA 105
Cdd:smart00410   1 PPSVTVKEGESVTLSCEASGSPP---PEVTWYKQGG-------------KLLAESGRFSVSRSGSTSTLTISNVTPEDSG 64

                   ....
gi 1104325227  106 DYYC 109
Cdd:smart00410  65 TYTC 68

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 1104325227  23 LTQPR-SVSGSPGQSVTISCTGTSSDVGGyNYVSWYQQHPGKAPKLMIY-----DVSKRPSGVPDRFSGSKSGN--TASL 94
Cdd:cd04982     1 LEQPQlSITREESKSVTISCKVSGIDFST-TYIHWYRQKPGQALERLLYvsstsAVRKDSGKTKNKFEARKDVGksTSTL 79

                          90       100
                  ....*....|....*....|....*.
gi 1104325227  95 TISGLQAEDEADYYCCSY-AGSYTFH 119
Cdd:cd04982    80 TITNLEKEDSATYYCAYWeSGSGYYI 105

Immunoglobulin (Ig) heavy chain (H), variable (V) domain; The members here are composed of the immunoglobulin (Ig) heavy chain (H), variable (V) domain. This group contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology. 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. There are five types of heavy chains (alpha, gamma, delta, epsilon, and mu), which determines the type of immunoglobulin formed: IgA, IgG, IgD, IgE, and IgM, respectively. In higher vertebrates, there are two types of light chain, designated kappa and lambda, which can associate with any of the heavy chains. This family includes alpha, gamma, delta, epsilon, and mu heavy chains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1104325227  23 LTQPRSVSGSPGQSVTISCTGTSSDVGGYnYVSWYQQHPGKAPKLM--IYDVSKRP---SGVPDRFSGS--KSGNTASLT 95
Cdd:cd04981     2 LQESGPGLVKPGQSLKLSCKASGFTFTSY-GMGWVRQAPGKGLEWIglIYPGGGDTyyaDSFKGRFTITrdTSKSTAYLQ 80

                          90       100
                  ....*....|....*....|.
gi 1104325227  96 ISGLQAEDEADYYCCSYAGSY 116
Cdd:cd04981    81 LNSLTSEDTAVYYCARGLGGY 101

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 1104325227  26 PRSVSGSPGQSVTISCTGTSSDVGGYNYVSWYQQHPGKAPKLMIYDVSKRPSgVP----DRFSG---SKSGNTASLTISG 98
Cdd:cd05718     6 PTEVTGFLGGSVTLPCSLTSPGTTKITQVTWMKIGAGSSQNVAVFHPQYGPS-VPnpyaERVEFlaaRLGLRNATLRIRN 84

                          90       100
                  ....*....|....*....|
gi 1104325227  99 LQAEDEAdYYCCSYAgsyTF 118
Cdd:cd05718    85 LRVEDEG-NYICEFA---TF 100

Immunoglobulin I-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1104325227  23 LTQPRSVSGSPGQSVTISC--TGTSSDVggynyVSWYQQhpgkapklmiyDVSKRPSgvpDRFSGSKSGNTASLTISGLQ 100
Cdd:pfam07679   4 TQKPKDVEVQEGESARFTCtvTGTPDPE-----VSWFKD-----------GQPLRSS---DRFKVTYEGGTYTLTISNVQ 64

                  ....*....
gi 1104325227 101 AEDEADYYC 109
Cdd:pfam07679  65 PDDSGKYTC 73

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 1104325227  23 LTQPRSVSGSPGQSVTISCTGT-------SSDVGGYnyvsWYQQHPGKAPKLMIYdVSKRPSGVPDRFS------GSKSG 89
Cdd:cd05712     3 LQMPKSVTVQEGLCVLIPCSFSypadywvSNPVHGY----WYRGGPYPKYRPPVA-TNNRTREVHESTQgrfrllGDPGK 77

                          90
                  ....*....|....*....
gi 1104325227  90 NTASLTISGLQAEDEADYY 108
Cdd:cd05712    78 KNCSLSISDARPEDSGKYF 96

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 1104325227  26 PRSVSGSPGQSVTISCTGTSSDVGGY-NYVSWyqQHPGKAPKLMIYDVSKRPS-GVPDR--FSGSKSG---NTASLTISG 98
Cdd:cd20989     6 PPEVRGFLGGSVTLPCHLLPPNMVTHvSQVTW--QRHDEHGSVAVFHPKQGPSfPESERlsFVAARLGaelRNASLAMFG 83

                          90
                  ....*....|.
gi 1104325227  99 LQAEDEADYYC 109
Cdd:cd20989    84 LRVEDEGNYTC 94