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 46254221  16 TLKESGPVLVKPTETLTLTCTVSGFSLSNARMGvsWIRQPPGKALEWLAHIFSND-EKSYSTSLKSRLTISKDTSKSQVV 94
Cdd:cd04981   1 QLQESGPGLVKPGQSLKLSCKASGFTFTSYGMG--WVRQAPGKGLEWIGLIYPGGgDTYYADSFKGRFTITRDTSKSTAY 78

                        90       100       110       120
                ....*....|....*....|....*....|....*....|
gi 46254221  95 LTMTNMDPVDTATYYCARIPLYYY--GMDVWGKGTTVTVS 132
Cdd:cd04981  79 LQLNSLTSEDTAVYYCARGLGGYGysYFDYWGQGTTVTVS 118

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 46254221  16 TLKESGPVLVKPTETLTLTCTVSGFSLSNARMGvsWIRQPPGKALEWLAHIFSND-EKSYSTSLKSRLTISKDTSKSQVV 94
Cdd:cd04981   1 QLQESGPGLVKPGQSLKLSCKASGFTFTSYGMG--WVRQAPGKGLEWIGLIYPGGgDTYYADSFKGRFTITRDTSKSTAY 78

                        90       100       110       120
                ....*....|....*....|....*....|....*....|
gi 46254221  95 LTMTNMDPVDTATYYCARIPLYYY--GMDVWGKGTTVTVS 132
Cdd:cd04981  79 LQLNSLTSEDTAVYYCARGLGGYGysYFDYWGQGTTVTVS 118

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 46254221    19 ESGPVLVKPTETLTLTCTVSGFSlSNARMGVSWIRQPPGKALEWLAHIFSNDEKSYSTslKSRLTISKDTSKSQVVLTMT 98
Cdd:pfam07686   2 TPREVTVALGGSVTLPCTYSSSM-SEASTSVYWYRQPPGKGPTFLIAYYSNGSEEGVK--KGRFSGRGDPSNGDGSLTIQ 78

                          90       100       110
                  ....*....|....*....|....*....|...
gi 46254221    99 NMDPVDTATYYCARIPlyyYGMDVWGKGTTVTV 131
Cdd:pfam07686  79 NLTLSDSGTYTCAVIP---SGEGVFGKGTRLTV 108

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 46254221  16 TLKESGPVLVKPTETLTLTCTVSGFSLSNARMGvsWIRQPPGKALEWLAHIFSND-EKSYSTSLKSRLTISKDTSKSQVV 94
Cdd:cd04981   1 QLQESGPGLVKPGQSLKLSCKASGFTFTSYGMG--WVRQAPGKGLEWIGLIYPGGgDTYYADSFKGRFTITRDTSKSTAY 78

                        90       100       110       120
                ....*....|....*....|....*....|....*....|
gi 46254221  95 LTMTNMDPVDTATYYCARIPLYYY--GMDVWGKGTTVTVS 132
Cdd:cd04981  79 LQLNSLTSEDTAVYYCARGLGGYGysYFDYWGQGTTVTVS 118

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 46254221  23 VLVKPTETLTLTCTVSGFSLSNarmGVSWIRQPPGKALEWLAHIFSNDEKSYSTSlKSRLTISKDTSKSqVVLTMTNMDP 102
Cdd:cd00099   8 LSVQEGESVTLSCEVSSSFSST---YIYWYRQKPGQGPEFLIYLSSSKGKTKGGV-PGRFSGSRDGTSS-FSLTISNLQP 82

                        90       100
                ....*....|....*....|....*....
gi 46254221 103 VDTATYYCARIPLYYYGMDVWGKGTTVTV 131
Cdd:cd00099  83 EDSGTYYCAVSESGGTDKLTFGSGTRLTV 111

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 46254221  27 PTETLTLTCTVSGFSLSNARmgVSWIRQPPGKALEWLAHIFSNDEKSYST-SLKSRLTISKDTSKSQVVLTMTNMDPVDT 105
Cdd:cd04982  12 ESKSVTISCKVSGIDFSTTY--IHWYRQKPGQALERLLYVSSTSAVRKDSgKTKNKFEARKDVGKSTSTLTITNLEKEDS 89

                        90       100       110
                ....*....|....*....|....*....|
gi 46254221 106 ATYYCA---RIPLYYYgmDVWGKGTTVTVS 132
Cdd:cd04982  90 ATYYCAyweSGSGYYI--KVFGSGTKLIVT 117

T-cell receptor Mu, Heavy chain, variable (V) domain; The members here are composed of the immunoglobulin (Ig) heavy chain (H), variable (V) domain of the T-cell receptor Mu. 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. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 46254221  17 LKESGPVLVKPTETLTLTCTVSGFSLSNARMGvsWIRQPPGKALEWLAhifSNDEKSYSTSlKSRLTISKDTSKSQVVLT 96
Cdd:cd16095   4 LEESGGGSHPAGKTLSLKCQTSGFQFNTSQLS--WYLWVPGHAPLWLT---SLDHISTKVS-EDRITSSREDTNSQIFLQ 77

                        90       100       110
                ....*....|....*....|....*....|....*....
gi 46254221  97 MTNMDPVDTATYYCARipLYYYGMD----VWGKGTTVTV 131
Cdd:cd16095  78 IKGLGLRDSGQYHCAR--RVGYGDDtdklIFGPGTDVIV 114

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 46254221  49 VSWIRQPPGKALEWLAHIFSNDEKSYSTSLKSRLTISKdTSKSQVVLTMTNMDPVDTATYYCA------RIPLYYygmdv 122
Cdd:cd05899  29 MYWYRQDPGKGLQLLFYSYGGGLNEEGDLPGDRFSASR-PSLTRSSLTIKSAEPEDSAVYLCAsslgggADEAYF----- 102

                ....*....
gi 46254221 123 wGKGTTVTV 131
Cdd:cd05899 103 -GPGTRLTV 110

CH1 domain (first constant Ig domain of the heavy chain) in immunoglobulin heavy mu chain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the first immunoglobulin constant-1 set domain of mu chains. It belongs to a family composed of the first immunoglobulin constant-1 set domain of alpha, delta, epsilon, gamma, and mu heavy chains. This domain is found on the Fab antigen-binding fragment. 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 is composed of a constant domain and a variable domain. There are five types of heavy chains: alpha, delta, epsilon, gamma, and mu, all consisting of a variable domain (VH) with three (alpha, delta and gamma) or four (epsilon and mu) constant domains (CH1 to CH4). Ig molecules are modular proteins, in which the variable and constant domains have clear, conserved sequence patterns. This group belongs to the C1-set of IgSF domains, which are classical Ig-like domains resembling the antibody constant domain. C1-set domains are found almost exclusively in molecules involved in the immune system, such as in immunoglobulin light and heavy chains, in the major histocompatibility complex (MHC) class I and II complex molecules, and in various T-cell receptors.

                        10        20        30
                ....*....|....*....|....*....|
gi 46254221 138 APTLFPLVSCENSPSDtsSVAVGCLAQDFL 167
Cdd:cd21819   1 APTLFPLVSCGSSTSD--PVTVGCLATDFL 28

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 46254221  21 GPVLVKPTETLTLTCTVSGFSLSnarMGVSWIRQPPG----KALEWLAHIFSNDEKSYSTSLKS-RLTISKDTSKSQVVL 95
Cdd:cd07700   6 GSLLVQTNQTVKMSCEAKTSPKN---TRIYWLRQRQApskdSHFEFLASWDPSKGIVYGEGVDQeKLIILSDSDSSRYIL 82

                        90       100       110
                ....*....|....*....|....*....|....*...
gi 46254221  96 TMTNMDPVDTATYYCARI--PlyyygMDVWGKGTTVTV 131
Cdd:cd07700  83 SLMSVKPEDSGTYFCMTVgsP-----ELIFGTGTKLSV 115

CH1 domain (first constant Ig domain of the heavy chain) in immunoglobulin heavy alpha, delta, epsilon, gamma, and mu chains; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the first immunoglobulin constant-1 set domain of alpha, delta, epsilon, gamma, and mu heavy chains. This domain is found on the Fab antigen-binding fragment. 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 is composed of a constant domain and a variable domain. There are five types of heavy chains: alpha, delta, epsilon, gamma, and mu, all consisting of a variable domain (VH) with three (alpha, delta and gamma) or four (epsilon and mu) constant domains (CH1 to CH4). Ig molecules are modular proteins, in which the variable and constant domains have clear, conserved sequence patterns. This group belongs to the C1-set of IgSF domains, which are classical Ig-like domains resembling the antibody constant domain. C1-set domains are found almost exclusively in molecules involved in the immune system, such as in immunoglobulin light and heavy chains, in the major histocompatibility complex (MHC) class I and II complex molecules, and in various T-cell receptors.

                        10        20        30
                ....*....|....*....|....*....|
gi 46254221 138 APTLFPLVSCENSPSdTSSVAVGCLAQDFL 167
Cdd:cd04985   1 APTVFPLQSATKSQS-NGPVALGCLISDYF 29

Immunoglobulin (Ig)-like variable (V) domain of Cluster of Differentiation (CD) 8 alpha chain; The members here are composed of the immunoglobulin (Ig)-like variable domain of the Cluster of Differentiation (CD) 8 alpha. 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. The Ig domain of CD8 alpha binds to antibodies. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 46254221  29 ETLTLTCTVsgfsLSNARMGVSWIRQPPGKA--LEWLAHIFSNDEKSYSTSLKS-RLTISKDTSKsqVVLTMTNMDPVDT 105
Cdd:cd05720  14 QKVELVCEV----LNSVPQGCSWLFQPRGSApqPTFLLYLSSSNKTKWAEGLDSkRFSGSRSGSS--YVLTLKDFRKEDE 87

                ....*
gi 46254221 106 ATYYC 110
Cdd:cd05720  88 GYYFC 92