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 309350    22 QLQQPGAVLVRHGASVKLSCKASGYTFTSSWMHWAKQRHGQGLEWIGEIHPNSGNTNYNEKFKGKATLTVDKSSSTAYVD 101
Cdd:cd04981   1 QLQESGPGLVKPGQSLKLSCKASGFTFTSYGMGWVRQAPGKGLEWIGLIYPGGGDTYYADSFKGRFTITRDTSKSTAYLQ 80

                        90
                ....*....|....*..
gi 309350   102 LSSLTSEDSAVYYCARH 118
Cdd:cd04981  81 LNSLTSEDTAVYYCARG 97

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 309350    22 QLQQPGAVLVRHGASVKLSCKASGYTFTSSWMHWAKQRHGQGLEWIGEIHPNSGNTNYNEKFKGKATLTVDKSSSTAYVD 101
Cdd:cd04981   1 QLQESGPGLVKPGQSLKLSCKASGFTFTSYGMGWVRQAPGKGLEWIGLIYPGGGDTYYADSFKGRFTITRDTSKSTAYLQ 80

                        90
                ....*....|....*..
gi 309350   102 LSSLTSEDSAVYYCARH 118
Cdd:cd04981  81 LNSLTSEDTAVYYCARG 97

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 309350      24 QQPGAVLVRHGASVKLSCKASGY-TFTSSWMHWAKQRHGQGLEWigEIHPNSGNTNyNEKFKGKATLTVDKSSSTAYVDL 102
Cdd:pfam07686   1 QTPREVTVALGGSVTLPCTYSSSmSEASTSVYWYRQPPGKGPTF--LIAYYSNGSE-EGVKKGRFSGRGDPSNGDGSLTI 77

                          90
                  ....*....|....
gi 309350     103 SSLTSEDSAVYYCA 116
Cdd:pfam07686  78 QNLTLSDSGTYTCA 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 309350    22 QLQQPGAVLVRHGASVKLSCKASGYTFTSSWMHWAKQRHGQGLEWIGEIHPNSGNTNYNEKFKGKATLTVDKSSSTAYVD 101
Cdd:cd04981   1 QLQESGPGLVKPGQSLKLSCKASGFTFTSYGMGWVRQAPGKGLEWIGLIYPGGGDTYYADSFKGRFTITRDTSKSTAYLQ 80

                        90
                ....*....|....*..
gi 309350   102 LSSLTSEDSAVYYCARH 118
Cdd:cd04981  81 LNSLTSEDTAVYYCARG 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 309350    24 QQPGAVLVRHGASVKLSCKASGyTFTSSWMHWAKQRHGQGLEWIGEIhpNSGNTNYNEKFKGKATLTVDKSSStAYVDLS 103
Cdd:cd00099   3 QSPRSLSVQEGESVTLSCEVSS-SFSSTYIYWYRQKPGQGPEFLIYL--SSSKGKTKGGVPGRFSGSRDGTSS-FSLTIS 78

                        90
                ....*....|....
gi 309350   104 SLTSEDSAVYYCAR 117
Cdd:cd00099  79 NLQPEDSGTYYCAV 92

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 309350    23 LQQPGAVLVRH-GASVKLSCKASGYTFTSSWMHWAKQRHGQGLEWIGEIHPNSGNTNYNEKFKGKATLTVDKSSSTAYVD 101
Cdd:cd04982   1 LEQPQLSITREeSKSVTISCKVSGIDFSTTYIHWYRQKPGQALERLLYVSSTSAVRKDSGKTKNKFEARKDVGKSTSTLT 80

                        90
                ....*....|....*.
gi 309350   102 LSSLTSEDSAVYYCAR 117
Cdd:cd04982  81 ITNLEKEDSATYYCAY 96

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 309350    23 LQQPGAVLVRHGASVKLSCKASGYTfTSSWMHWAKQRHG----QGLEWIGEIHPnSGNTNYNEKFKG-KATLTVDKSSST 97
Cdd:cd07700   2 LQTPGSLLVQTNQTVKMSCEAKTSP-KNTRIYWLRQRQApskdSHFEFLASWDP-SKGIVYGEGVDQeKLIILSDSDSSR 79

                        90
                ....*....|....*....
gi 309350    98 AYVDLSSLTSEDSAVYYCA 116
Cdd:cd07700  80 YILSLMSVKPEDSGTYFCM 98

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 309350    23 LQQPGAVLVRHGASVKLSCKASGYTFTSSWMHWAKQRHGQGLEWIgeIHPNSGNTN-YNEKFKGKatltvdKSSSTAYVD 101
Cdd:cd04984   2 LTQPSSLSVSPGETVTITCTGSSGNISGNYVNWYQQKPGSAPRYL--IYEDKHRPSgIPDRFSGS------KSGNTASLT 73

                        90
                ....*....|....*
gi 309350   102 LSSLTSEDSAVYYCA 116
Cdd:cd04984  74 ISGAQTEDEADYYCQ 88

Immunoglobulin (Ig) light chain, kappa type, variable (V) domain; The members here are composed of the immunoglobulin (Ig) light chain, kappa type, 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. 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.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 309350    24 QQPGAVLVRHGASVKLSCKASGyTFTSSWMHWAKQRHGQGLEWIgeIH-PNSGNTNYNEKFKGKAtltvdksSSTAY-VD 101
Cdd:cd04980   5 QSPASLSVSPGERVTISCKASQ-SISSNYLAWYQQKPGQAPKLL--IYyASTLHSGVPSRFSGSG-------SGTDFtLT 74

                        90
                ....*....|....
gi 309350   102 LSSLTSEDSAVYYC 115
Cdd:cd04980  75 ISSVEPEDAAVYYC 88

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 309350    20 QVQLQQPgAVLVRHGASVKLSCkasgyTFTSSW----MHWAKQRHGQGLEWIgeIHPNSGNTNyneKFKGKATLTVDKSS 95
Cdd:cd07706   1 KVTQAQP-DVSVQVGEEVTLNC-----RYETSWtnyyLFWYKQLPSGEMTFL--IRQDSSEQN---AKSGRYSVNFQKAQ 69

                        90       100
                ....*....|....*....|.
gi 309350    96 STAYVDLSSLTSEDSAVYYCA 116
Cdd:cd07706  70 KSISLTISALQLEDSAKYFCA 90