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 311706665   3 QLVESRGVLVQPGGSLRLSCAASGFTVSSNEMSWVRQAPGKGLEWVSSIS--GGSTYYADSRKGRFTISRDNSKNTLHLQ 80
Cdd:cd04981    1 QLQESGPGLVKPGQSLKLSCKASGFTFTSYGMGWVRQAPGKGLEWIGLIYpgGGDTYYADSFKGRFTITRDTSKSTAYLQ 80

                         90
                 ....*....|....
gi 311706665  81 MNSLRAEDTAVYYC 94
Cdd:cd04981   81 LNSLTSEDTAVYYC 94

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 311706665   3 QLVESRGVLVQPGGSLRLSCAASGFTVSSNEMSWVRQAPGKGLEWVSSIS--GGSTYYADSRKGRFTISRDNSKNTLHLQ 80
Cdd:cd04981    1 QLQESGPGLVKPGQSLKLSCKASGFTFTSYGMGWVRQAPGKGLEWIGLIYpgGGDTYYADSFKGRFTITRDTSKSTAYLQ 80

                         90
                 ....*....|....
gi 311706665  81 MNSLRAEDTAVYYC 94
Cdd:cd04981   81 LNSLTSEDTAVYYC 94

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 311706665    5 VESRGVLVQPGGSLRLSCAASGFTVS-SNEMSWVRQAPGKGLEWVssISGGSTYYADSR-KGRFTISRDNSKNTLHLQMN 82
Cdd:pfam07686   1 QTPREVTVALGGSVTLPCTYSSSMSEaSTSVYWYRQPPGKGPTFL--IAYYSNGSEEGVkKGRFSGRGDPSNGDGSLTIQ 78

                          90
                  ....*....|...
gi 311706665   83 SLRAEDTAVYYCK 95
Cdd:pfam07686  79 NLTLSDSGTYTCA 91

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 311706665   3 QLVESRGVLVQPGGSLRLSCAASGFTVSSNEMSWVRQAPGKGLEWVSSIS--GGSTYYADSRKGRFTISRDNSKNTLHLQ 80
Cdd:cd04981    1 QLQESGPGLVKPGQSLKLSCKASGFTFTSYGMGWVRQAPGKGLEWIGLIYpgGGDTYYADSFKGRFTITRDTSKSTAYLQ 80

                         90
                 ....*....|....
gi 311706665  81 MNSLRAEDTAVYYC 94
Cdd:cd04981   81 LNSLTSEDTAVYYC 94

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 311706665   7 SRGVLVQPGGSLRLSCAASGFTVSSNeMSWVRQAPGKGLEWVSSISGGSTYYADSRKGRFTISRDnSKNTLHLQMNSLRA 86
Cdd:cd00099    5 PRSLSVQEGESVTLSCEVSSSFSSTY-IYWYRQKPGQGPEFLIYLSSSKGKTKGGVPGRFSGSRD-GTSSFSLTISNLQP 82

                 ....*...
gi 311706665  87 EDTAVYYC 94
Cdd:cd00099   83 EDSGTYYC 90

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

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 311706665    7 SRGVLVQPGGSLRLSCAASGFtvSSNEMSWVRQapgkGLEWVSSisggstyyadsrKGRFTISRDNskNTLHLQMNSLRA 86
Cdd:smart00410  1 PPSVTVKEGESVTLSCEASGS--PPPEVTWYKQ----GGKLLAE------------SGRFSVSRSG--STSTLTISNVTP 60

                  ....*...
gi 311706665   87 EDTAVYYC 94
Cdd:smart00410 61 EDSGTYTC 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 311706665  13 QPGGSLRLSCAASGFTVSSNEMSWVRQAPGKGLEWVSSISGGST--YYADSRKGRFTISRDNSKNTLHLQMNSLRAEDTA 90
Cdd:cd04982   11 EESKSVTISCKVSGIDFSTTYIHWYRQKPGQALERLLYVSSTSAvrKDSGKTKNKFEARKDVGKSTSTLTITNLEKEDSA 90

                 ....
gi 311706665  91 VYYC 94
Cdd:cd04982   91 TYYC 94

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 311706665  12 VQPGGSLRLSCAASgfTVSSNEMSWVRQAPGKGLEWVSSISGGSTyyaDSRKGRFTISRDNSKNTLHLQMNSLRAEDTAV 91
Cdd:cd04983   10 VQEGENVTLNCNYS--TSTFYYLFWYRQYPGQGPQFLIYISSDSG---NKKKGRFSATLDKSRKSSSLHISAAQLSDSAV 84

                 ...
gi 311706665  92 YYC 94
Cdd:cd04983   85 YFC 87

Immunoglobulin (Ig) variable (V) domain of Cluster of Differentiation (CD) 8 beta chain; The members here are composed of the immunoglobulin (Ig)-like domain in Cluster of Differentiation (CD) 8 beta. The CD8 glycoprotein plays an essential role in the control of T-cell selection, maturation, and the T-cell receptor (TCR)-mediated response to peptide antigen. CD8 is comprised of alpha and beta subunits and is expressed as either an alpha/alpha or alpha/beta dimer. Both dimeric isoforms can serve as a coreceptor for T cell activation and differentiation, however they have distinct physiological roles, different cellular distributions, unique binding partners, etc. Each CD8 subunit is comprised of an extracellular domain containing a V-type Ig-like domain, a single pass transmembrane portion, and a short intracellular domain. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 311706665  10 VLVQPGGSLRLSCAASGFTvSSNEMSWVR--QAPGKG------LEWVSSisGGSTYYADSRKGRFTISRDNSKNTLHLQM 81
Cdd:cd07700    8 LLVQTNQTVKMSCEAKTSP-KNTRIYWLRqrQAPSKDshfeflASWDPS--KGIVYGEGVDQEKLIILSDSDSSRYILSL 84

                         90
                 ....*....|...
gi 311706665  82 NSLRAEDTAVYYC 94
Cdd:cd07700   85 MSVKPEDSGTYFC 97

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
                 ....*....|....*....|....*....|....*....|....*....|....*....
gi 311706665  36 WVRQAPGKGLEWVssISGGStYYADSRKGRFTISRDNSKNTLHLQMNSLRAEDTAVYYC 94
Cdd:cd07706   34 WYKQLPSGEMTFL--IRQDS-SEQNAKSGRYSVNFQKAQKSISLTISALQLEDSAKYFC 89

Immunoglobulin (Ig)-like domain in the polymeric Ig receptor (pIgR) and similar proteins; The members here are composed of the immunoglobulin (Ig)-like domain in the polymeric Ig receptor (pIgR) and similar proteins. pIgR delivers dimeric IgA and pentameric IgM to mucosal secretions. Polymeric immunoglobulin (pIgs) are the first defense against pathogens and toxins. IgA and IgM can form polymers via an 18-residue extension at their C-termini referred to as the tailpiece. pIgR transports pIgs across mucosal epithelia into mucosal secretions. Human pIgR is a glycosylated type I transmembrane protein, comprised of a 620-residue extracellular region, a 23-residue transmembrane region, and a 103-residue cytoplasmic tail. The extracellular region contains five domains that share sequence similarity with Ig variable (v) regions. This group also contains the Ig-like extracellular domains of other receptors such as NK cell receptor Nkp44 and myeloid receptors, among others.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 311706665  10 VLVQPGGSLRLSCAASGfTVSSNEMSWVRQAPGKGLEWVSSISggstyyaDSRKGRFTISRDNSKNTLHLQMNSLRAEDT 89
Cdd:cd05716    7 VTGVEGGSVTIQCPYPP-KYASSRKYWCKWGSEGCQTLVSSEG-------VVPGGRISLTDDPDNGVFTVTLNQLRKEDA 78

                 ....*
gi 311706665  90 AVYYC 94
Cdd:cd05716   79 GWYWC 83