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 768041374  29 QLQESGPGLVKPSETLSLTCTVSGYSISSgYYWGWIRQPPGKGLEWIGSIY-HSGSTYYNPSLKSRVTISVDTSKNQFSL 107
Cdd:cd04981    1 QLQESGPGLVKPGQSLKLSCKASGFTFTS-YGMGWVRQAPGKGLEWIGLIYpGGGDTYYADSFKGRFTITRDTSKSTAYL 79

                         90
                 ....*....|....*....
gi 768041374 108 KLSSVTAADTAVYYCARDT 126
Cdd:cd04981   80 QLNSLTSEDTAVYYCARGL 98

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 768041374  29 QLQESGPGLVKPSETLSLTCTVSGYSISSgYYWGWIRQPPGKGLEWIGSIY-HSGSTYYNPSLKSRVTISVDTSKNQFSL 107
Cdd:cd04981    1 QLQESGPGLVKPGQSLKLSCKASGFTFTS-YGMGWVRQAPGKGLEWIGLIYpGGGDTYYADSFKGRFTITRDTSKSTAYL 79

                         90
                 ....*....|....*....
gi 768041374 108 KLSSVTAADTAVYYCARDT 126
Cdd:cd04981   80 QLNSLTSEDTAVYYCARGL 98

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 768041374   31 QESGPGLVKPSETLSLTCTVSGYSISSGYYWGWIRQPPGKGLEWIgsIYHSGSTYYNPSLKSRVTISVDTSKNQFSLKLS 110
Cdd:pfam07686   1 QTPREVTVALGGSVTLPCTYSSSMSEASTSVYWYRQPPGKGPTFL--IAYYSNGSEEGVKKGRFSGRGDPSNGDGSLTIQ 78

                          90
                  ....*....|...
gi 768041374  111 SVTAADTAVYYCA 123
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 768041374  29 QLQESGPGLVKPSETLSLTCTVSGYSISSgYYWGWIRQPPGKGLEWIGSIY-HSGSTYYNPSLKSRVTISVDTSKNQFSL 107
Cdd:cd04981    1 QLQESGPGLVKPGQSLKLSCKASGFTFTS-YGMGWVRQAPGKGLEWIGLIYpGGGDTYYADSFKGRFTITRDTSKSTAYL 79

                         90
                 ....*....|....*....
gi 768041374 108 KLSSVTAADTAVYYCARDT 126
Cdd:cd04981   80 QLNSLTSEDTAVYYCARGL 98

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 768041374  31 QESGPGLVKPSETLSLTCTVSGYSISSGYYWgwIRQPPGKGLEWIGSIYhSGSTYYNPSLKSRVTISVDTSKnQFSLKLS 110
Cdd:cd00099    3 QSPRSLSVQEGESVTLSCEVSSSFSSTYIYW--YRQKPGQGPEFLIYLS-SSKGKTKGGVPGRFSGSRDGTS-SFSLTIS 78

                         90       100
                 ....*....|....*....|
gi 768041374 111 SVTAADTAVYYCARDTVRGG 130
Cdd:cd00099   79 NLQPEDSGTYYCAVSESGGT 98

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 768041374  42 ETLSLTCTvsgYSISSGYYWGWIRQPPGKGLEWIgsIYhsGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYY 121
Cdd:cd04983   14 ENVTLNCN---YSTSTFYYLFWYRQYPGQGPQFL--IY--ISSDSGNKKKGRFSATLDKSRKSSSLHISAAQLSDSAVYF 86

                 ..
gi 768041374 122 CA 123
Cdd:cd04983   87 CA 88

Gammadelta T-cell antigen receptor, variable (V) domain; The members here are composed of the immunoglobulin (Ig) variable (V) domain of the 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 768041374  38 VKPSETLSLTCTVSGYSISSgYYWGWIRQPPGKGLEWIgsiYHSGSTYyNPSLKSRVTISVDTSKNQFSLKLSSVTAADT 117
Cdd:cd20988   10 VSVGKPVTLKCSMKGEAISN-YYINWYRKTQGNTMTFI---YREGGIY-GPGFKDNFRGDIDSSNNLAVLKILEASERDE 84

                         90
                 ....*....|....
gi 768041374 118 AVYYCARDTVRGGE 131
Cdd:cd20988   85 GSYYCASDTPGGGR 98

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 768041374    33 SGPGLVKPSETLSLTCTVSGYSISSGYywgWIRQppgkGLEWIGSiyhsgstyynpslKSRvtISVDTSKNQFSLKLSSV 112
Cdd:smart00410   1 PPSVTVKEGESVTLSCEASGSPPPEVT---WYKQ----GGKLLAE-------------SGR--FSVSRSGSTSTLTISNV 58

                           90
                   ....*....|.
gi 768041374   113 TAADTAVYYCA 123
Cdd:smart00410  59 TPEDSGTYTCA 69

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 768041374  30 LQESGPGLVKPSETLSLTCTVSGYSISSGYYWGWIRQPPGKG--LEWIGSIYHSGSTYYNPSLKS-RVTISVDTSKNQFS 106
Cdd:cd07700    2 LQTPGSLLVQTNQTVKMSCEAKTSPKNTRIYWLRQRQAPSKDshFEFLASWDPSKGIVYGEGVDQeKLIILSDSDSSRYI 81

                         90
                 ....*....|....*..
gi 768041374 107 LKLSSVTAADTAVYYCA 123
Cdd:cd07700   82 LSLMSVKPEDSGTYFCM 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 768041374  38 VKPSETLSLTCTVSGYSISsGYYWGWIRQPPGKGLEWIgsIYHSGSTyyNPSLKSRVTISvdTSKNQFSLKLSSVTAADT 117
Cdd:cd04984   10 VSPGETVTITCTGSSGNIS-GNYVNWYQQKPGSAPRYL--IYEDKHR--PSGIPDRFSGS--KSGNTASLTISGAQTEDE 82

                 ....*.
gi 768041374 118 AVYYCA 123
Cdd:cd04984   83 ADYYCQ 88

Immunoglobulin (Ig)-like variable (V) domain of the Signal-Regulatory Protein (SIRP); The members here are composed of the immunoglobulin (Ig)-like domain of the Signal-Regulatory Protein (SIRP). The SIRPs belong to the "paired receptors" class of membrane proteins that comprise several genes coding for proteins with similar extracellular regions, but very different transmembrane/cytoplasmic regions with different (activating or inhibitory) signaling potentials. They are commonly on NK cells, but are also on many myeloid cells. Their extracellular region contains three immunoglobulin superfamily domains, a single V-set, and two C1-set IgSF domains. Their cytoplasmic tails that contain either ITIMs or transmembrane regions have positively charged residues that allow an association with adaptor proteins, such as DAP12/KARAP, containing ITAMs. There are 3 distinct SIRP members: alpha, beta, and gamma. SIRP alpha (also known as CD172a or SRC homology 2 domain-containing protein tyrosine phosphatase substrate 1/Shps-1) is a membrane receptor that interacts with a ligand CD47 expressed on many cells and gives an inhibitory signal through immunoreceptor tyrosine-based inhibition motifs in the cytoplasmic region that interact with phosphatases SHP-1 and SHP-2. SIRP beta has a short cytoplasmic region and associates with a transmembrane adapter protein DAP12 containing immunoreceptor tyrosine-based activation motifs to give an activating signal. SIRP gamma contains a very short cytoplasmic region lacking obvious signaling motifs, but also binds CD47 with much less affinity. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 768041374  37 LVKPSETLSLTCTVSGYsISSGYYwGWIRQP-PGKGLewigsIYHSGSTYYnpslkSRVTISVDTSKNQ---FSLKLSSV 112
Cdd:cd16097   10 SVAAGESATLHCTVTSL-IPVGPI-QWFRGAgPGREL-----IYNQKEGHF-----PRVTTVSDLTKRNnmdFSIRISNI 77

                         90
                 ....*....|..
gi 768041374 113 TAADTAVYYCAR 124
Cdd:cd16097   78 TPADAGTYYCVK 89