Immunoglobulin light chain Constant domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) light chain constant (C) domain. 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 determine the type of immunoglobulin: 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 1622857065 134 APSVFIFPPSEDQVTSGTVSVVCLLNNFYPREASVKWKVDGVLKTGNSQESVTEQDSkDNTYSLSSTLTLSSTDYQSHNV 213
Cdd:cd07699     1 APSVTIFPPSSEELSSGKATLVCLINKFYPGFATVTWKVDGSTVSSGVTTSKTEQQS-DNTYSMSSYLTLSSSDWNKHKV 79

                          90       100
                  ....*....|....*....|
gi 1622857065 214 YACEVTHQGLSSPVTKSFNR 233
Cdd:cd07699    80 YTCEVTHEGLSSTITKSFNR 99

Immunoglobulin light chain Constant domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) light chain constant (C) domain. 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 determine the type of immunoglobulin: 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 1622857065 134 APSVFIFPPSEDQVTSGTVSVVCLLNNFYPREASVKWKVDGVLKTGNSQESVTEQDSkDNTYSLSSTLTLSSTDYQSHNV 213
Cdd:cd07699     1 APSVTIFPPSSEELSSGKATLVCLINKFYPGFATVTWKVDGSTVSSGVTTSKTEQQS-DNTYSMSSYLTLSSSDWNKHKV 79

                          90       100
                  ....*....|....*....|
gi 1622857065 214 YACEVTHQGLSSPVTKSFNR 233
Cdd:cd07699    80 YTCEVTHEGLSSTITKSFNR 99

Immunoglobulin V-Type;

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 1622857065   41 VTITCRASQG--ISTYLNWYQQKPGKAPKRLIYAASS----LESGVPSRFSGSG--SGTDFTLTISSLQPEDFATYYC 110
Cdd:smart00406   2 VTLSCKFSGStfSSYYVSWVRQPPGKGLEWLGYIGSNgssyYQESYKGRFTISKdtSKNDVSLTISNLRVEDTGTYYC 79

Immunoglobulin C-Type;

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*.
gi 1622857065  151 TVSVVCLLNNFYPREASVKWKVDGVLKTGNSQESVTEQDSkDNTYSLSSTLTLSSTDYQSHNVYACEVTHQGLSSP 226
Cdd:smart00407   1 KATLVCLVSGFYPPDITVTWLRNGQEVTEGVSTTDPLKNS-DGTYFLSSYLTVPASTWESGDVYTCQVTHEGLKEP 75

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 1622857065  26 MTQsPSSLSASAGDRVTITCRASQGIST--YLNWYQQKPGKAPKRLIYAASSLESGVPSRFSGSGSGTDFTLTISSLQPE 103
Cdd:cd04984     2 LTQ-PSSLSVSPGETVTITCTGSSGNISgnYVNWYQQKPGSAPRYLIYEDKHRPSGIPDRFSGSKSGNTASLTISGAQTE 80

                          90       100
                  ....*....|....*....|...
gi 1622857065 104 DFATYYCLQYNSNPFTFGPGTKL 126
Cdd:cd04984    81 DEADYYCQVWDSNSYVFGGGTKL 103

Immunoglobulin light chain Constant domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) light chain constant (C) domain. 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 determine the type of immunoglobulin: 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 1622857065 134 APSVFIFPPSEDQVTSGTVSVVCLLNNFYPREASVKWKVDGVLKTGNSQESVTEQDSkDNTYSLSSTLTLSSTDYQSHNV 213
Cdd:cd07699     1 APSVTIFPPSSEELSSGKATLVCLINKFYPGFATVTWKVDGSTVSSGVTTSKTEQQS-DNTYSMSSYLTLSSSDWNKHKV 79

                          90       100
                  ....*....|....*....|
gi 1622857065 214 YACEVTHQGLSSPVTKSFNR 233
Cdd:cd07699    80 YTCEVTHEGLSSTITKSFNR 99

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 1622857065  27 TQSPSSLSASAGDRVTITCRASQGiSTYLNWYQQKPGKAPKRLIYAASSL---ESGVP-SRFSGSG-SGTDFTLTISSLQ 101
Cdd:cd05899     2 TQSPRYLIKRRGQSVTLRCSQKSG-HDNMYWYRQDPGKGLQLLFYSYGGGlneEGDLPgDRFSASRpSLTRSSLTIKSAE 80

                          90       100
                  ....*....|....*....|....*...
gi 1622857065 102 PEDFATYYC---LQYNSNPFTFGPGTKL 126
Cdd:cd05899    81 PEDSAVYLCassLGGGADEAYFGPGTRL 108

Immunoglobulin Constant-1 (C1)-set domain; The members here are composed of C1-set domains, classical Ig-like domains resembling the antibody constant domain. Members of the IgC1 family are components of immunoglobulin, T-cell receptors, CD1 cell surface glycoproteins, secretory glycoproteins A/C, and major histocompatibility complex (MHC) class I/II molecules. In immunoglobulins, each chain is composed of one variable domain (IgV) and one or more IgC domains. These names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. The IgV domain is responsible for antigen binding, while the IgC domain is involved in oligomerization and molecular interactions. 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 strands by G, F, C, and C'.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1622857065 136 SVFIFPPSEDQVTSGTVSVVCLLNNFYPREASVKWKVDGVLKTGNSQESvTEQDSKDNTYSLSSTLTLSSTDYQSHNVYA 215
Cdd:cd00098     1 TVTLLPPSPEEKGGGKVTLVCLVSGFYPKDITVTWLKNGVPLTSGVSTS-SPVEPNDGTYSVTSSLTVPPSDWDEGATYT 79

                          90
                  ....*....|....*.
gi 1622857065 216 CEVTHQGLSSPVTKSF 231
Cdd:cd00098    80 CVVTHESLKSPLSKTW 95

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 1622857065  28 QSPSSLSASAGDRVTITCRAS---QGISTYLNWYQQKPGKAPKRLIYAASSL--ESGVPSRFSGSG--SGTDFTLTISSL 100
Cdd:pfam07686   1 QTPREVTVALGGSVTLPCTYSssmSEASTSVYWYRQPPGKGPTFLIAYYSNGseEGVKKGRFSGRGdpSNGDGSLTIQNL 80

                          90       100
                  ....*....|....*....|....*.
gi 1622857065 101 QPEDFATYYCLQYNSNPFTFGPGTKL 126
Cdd:pfam07686  81 TLSDSGTYTCAVIPSGEGVFGKGTRL 106

CH3 domain (third constant Ig domain of the heavy chain) in immunoglobulin heavy alpha, gamma, and delta chains, and CH4 domain (fourth constant Ig domain of the heavy chain) in immunoglobulin heavy alpha, epsilon, and mu chains; member of the C1-set of I; The members here are composed of the third and fourth immunoglobulin constant domain (IgC) of alpha, delta, gamma and alpha, epsilon, and mu heavy chains, respectively. This domain is found on the Fc 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.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1622857065 135 PSVFIFPPSEDQVTSG-TVSVVCLLNNFYPREASVKWKVDGV-LKTGNSQESVTEQDSkDNTYSLSSTLTLSSTDYQSHN 212
Cdd:cd05768     1 PSVYLLPPPEEELSLNeTVTLTCLVKGFYPEDIFVSWLQNGEpLPSADYKTTAPVPES-DGSFFVYSKLNVSTADWNSGD 79

                          90       100
                  ....*....|....*....|..
gi 1622857065 213 VYACEVTHQGLSSPVT-KSFNR 233
Cdd:cd05768    80 VFSCVVGHEALPLQFTqKSIDK 101

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 1622857065  26 MTQSPSSLSASAGDRVTITCRASqGI---STYLNWYQQKPGKAPKRLIYAASS----LESGVPS-RFSGS--GSGTDFTL 95
Cdd:cd04982     1 LEQPQLSITREESKSVTISCKVS-GIdfsTTYIHWYRQKPGQALERLLYVSSTsavrKDSGKTKnKFEARkdVGKSTSTL 79

                          90       100       110
                  ....*....|....*....|....*....|....*
gi 1622857065  96 TISSLQPEDFATYYCL--QYNSNPFT--FGPGTKL 126
Cdd:cd04982    80 TITNLEKEDSATYYCAywESGSGYYIkvFGSGTKL 114

T cell receptor (TCR) beta chain constant immunoglobulin domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the T cell receptor (TCR) beta chain constant immunoglobulin domain. 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 beta chain. Alpha/beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. The antigen binding site is formed by the variable domains of the alpha and beta chains, located at the N-terminus of each chain. Alpha/beta TCRs recognize antigens differently from gamma/delta TCRs.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1622857065 134 APSVFIFPPSEDQVT-SGTVSVVCLLNNFYPREASVKWKVDGVLKTGNSQ-ESVTEQDSkDNTYSLSSTLTLSSTDYQS- 210
Cdd:cd05769     2 PPTVALFPPSEAEIRnKRKATLVCLATGFYPDHVSLSWKVNGKEVKDGVAtDPQALREN-TSTYSLSSRLRVSATEWFNp 80

                          90       100
                  ....*....|....*....|....*
gi 1622857065 211 HNVYACEVTHQGLSSpvTKSFNRGE 235
Cdd:cd05769    81 RNTFTCIVKFYGGTD--TDTWTQGI 103

CH2 domain (second constant Ig domain of the heavy chain) in immunoglobulin mu chain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin constant domain (IgC) of mu heavy chains. This domain is found on the Fc 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.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1622857065 135 PSVFIFPPS-EDQVTSGTVSVVCLLNNFYPREASVKWKVDGV-LKTGNSQESVTEQDSKDNTYSLSSTLTLSSTDYQSHN 212
Cdd:cd16093     2 PTVSLHAPSrEEFLGNRTATFVCLATGFSPKTISFKWLRNGKeVTSSTGAVVEEPKEDGKTLYSATSFLTITESEWKSQT 81

                          90
                  ....*....|.
gi 1622857065 213 VYACEVTHQGL 223
Cdd:cd16093    82 EFTCEFKHKGE 92

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 1622857065  25 QMTQSPSSLSASAGDRVTITCRASQGIST-YLNWYQqkpGKAPKR-LIYaaSSLESGVPsRFSGSGSGT-----DFTLTI 97
Cdd:cd16097     1 QVIQPEKSVSVAAGESATLHCTVTSLIPVgPIQWFR---GAGPGReLIY--NQKEGHFP-RVTTVSDLTkrnnmDFSIRI 74

                          90       100       110
                  ....*....|....*....|....*....|....*..
gi 1622857065  98 SSLQPEDFATYYCLQYNSNP-----FTFGPGTKLDIK 129
Cdd:cd16097    75 SNITPADAGTYYCVKFRKGSpddveFKSGAGTELSVR 111

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 1622857065  25 QMTQSPSSLsASAGDRVTITCRASQGI--STYLNWYQQKPGKAPK--RLIYAASSLE---SGVPSRFSGS--GSGTDFTL 95
Cdd:cd04981     1 QLQESGPGL-VKPGQSLKLSCKASGFTftSYGMGWVRQAPGKGLEwiGLIYPGGGDTyyaDSFKGRFTITrdTSKSTAYL 79

                          90
                  ....*....|....*
gi 1622857065  96 TISSLQPEDFATYYC 110
Cdd:cd04981    80 QLNSLTSEDTAVYYC 94

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1622857065  25 QMTQSPSSLSASAGDRVTITCRASQGISTYLNWYQQKPGKAPKRLIYAASSLESGvpsrfsgsgsgtdfTLTISSLQPED 104
Cdd:pfam13927   3 VITVSPSSVTVREGETVTLTCEATGSPPPTITWYKNGEPISSGSTRSRSLSGSNS--------------TLTISNVTRSD 68

                  ....*.
gi 1622857065 105 FATYYC 110
Cdd:pfam13927  69 AGTYTC 74

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        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1622857065 134 APSVFIFPPSEDQVTSGTVSVVCLLNNFYPREASVKWKVDGVLKTGNSQESVTEQDSKDNTYSLSSTLTLSSTDYQSHNV 213
Cdd:cd04985     1 APTVFPLQSATKSQSNGPVALGCLISDYFPESITVSWQKNTNSITSGFTRTFPVVLRSGGDYSCSSQLTVPLQEWNSGEV 80

                          90
                  ....*....|....*.
gi 1622857065 214 YACEVTHQGLSSPVTK 229
Cdd:cd04985    81 YKCQVQHSASNSKQEK 96

First immunoglobulin (Ig) domain of Cluster of Differentiation (CD) 4; member of the V-set of IgSF domains; The members here are composed of the first immunoglobulin (Ig) domain of Cluster of Differentiation (CD) 4. CD4 and CD8 are the two primary co-receptor proteins found on the surface of T cells, and the presence of either CD4 or CD8 determines the function of the T cell. CD4 is found on helper T cells, where it is required for the binding of MHC (major histocompatibility complex) class II molecules, while CD8 is found on cytotoxic T cells, where it is required for the binding of MHC class I molecules. CD4 contains four immunoglobulin domains, with the first three included in this hierarchy. The fourth domain has a general Ig architecture, but has slight topological changes in the arrangement of beta strands relative to the other structures in this family and is not specifically included in the hierarchy.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 1622857065  37 AGDRVTITCRASQGISTYLNW---YQQKP-GKAPKRLIYAASSLESGVPSRFSGSGSGTdFTLTISSLQPEDFATYYC 110
Cdd:cd07690     8 KGDTAELPCTASQKKSIQFHWknsNQIKIlGNQGSFLTKGPSKLNDRADSRRNLWDQGS-FPLIIKNLKIEDSDTYIC 84

CH3 domain (third constant Ig domain of heavy chains) in immunoglobulin heavy alpha, epsilon, and mu chains, and CH2 domain (second constant Ig domain of the gheavy chain) in immunoglobulin heavy gamma chain; member of the C1-set of Ig superfamily (IgSF) ; The members here are composed of the third immunoglobulin constant domain (IgC) of the gamma heavy chains and the second immunoglobulin constant domain (IgC) of alpha, epsilon, and mu heavy chains. This domain is found on the Fc 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.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1622857065 135 PSVFIFPPS-EDQVTSGTVSVVCLLNNF--YPrEASVKWKVdgvlKTGNSQESVTEQDSK--DNTYSLSSTLTLSSTDYQ 209
Cdd:cd07696     1 VSVFLIPPSpKDLFLTKSAKVTCLVVDLtsIE-EVNVTWSR----EDGNEVLASTTNPEKhyNATLSVVSTLTVCADDWD 75

                          90       100
                  ....*....|....*....|.
gi 1622857065 210 SHNVYACEVTHQGLSSPVTKS 230
Cdd:cd07696    76 NGKTFKCKVTHPDLPSPIVKS 96

Immunoglobulin variable domain (IgV) Cluster of Differentiation (CD) 79B; The members here are composed of the immunoglobulin variable domain (IgV) of the Cluster of Differentiation (CD) 79B (also known as CD79b molecule, immunoglobulin-associated beta (Ig-beta), and B29). The B lymphocyte antigen receptor is a multimeric complex that includes the antigen-specific component, surface immunoglobulin (Ig). Surface Ig non-covalently associates with two other proteins, Ig-alpha and Ig-beta, which are necessary for expression and function of the B-cell antigen receptor. This gene encodes the Ig-beta protein of the B-cell antigen component. Alternatively spliced transcript variants encoding different isoforms have been described. Members of the IgV family 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. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1622857065  28 QSPSSLSASAGDRVTITCRASQgiSTYLNWYQQKPGKAPKRLIyaassLESGvpsRFSGSGSGTDFTLTISSLQPEDFAT 107
Cdd:cd16096     3 QHPRFAAKKRSSMVKFHCYTNY--SGVMTWFRKKGNQRPQELF-----PEDG---RISQTQNGSVYTLTIQNIQYEDNGI 72

                          90       100
                  ....*....|....*....|..
gi 1622857065 108 YYCLQY--NSNP-FTFGPGTKL 126
Cdd:cd16096    73 YFCQQKcnSTEPdVTDGCGTEL 94

Fifth immunoglobulin (Ig)-like domain of Kirrel (kin of irregular chiasm-like) 3 protein; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the fifth immunoglobulin (Ig)-like domain of Kirrel (kin of irregular chiasm-like) 3 protein (also known as Neph2). This protein has five Ig-like domains, one transmembrane domain, and a cytoplasmic tail. Included in this group is mammalian Kirrel (Neph1). These proteins contain multiple Ig domains, have properties of cell adhesion molecules, and are important in organ development. Neph1 and 2 may mediate axonal guidance and synapse formation in certain areas of the CNS. In the kidney they participate in the formation of the slit diaphragm.

                          10        20        30        40        50        60
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 1622857065  66 PKRLIYA--ASSLESGVPSRF----SGSGSGTDFTLTISSLQPEDFATYY-CLQYNSnpftFGPGTKL 126
Cdd:cd05898    31 PDRIAWAwkENVLESGTLERYtverTSTGSGVLSTLTINNIMEADFQTHYnCTAWNS----FGSGTAI 94

Class Ia major histocompatibility complex (MHC) immunoglobulin domain of H2-Dd; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class Ia major histocompatibility complex (MHC) immunoglobulin domain of H2-Dd. Mouse MHC is composed of 11 subclasses. It includes the classical MHC class I (MHC-Ia) that comprises H-2D, H-2K and H-2L subclasses, the non-classical MHC class I (MHCIb) that comprises H-2Q, H-2M and H-2T subclasses, the classical MHC class II (MHC-IIa) that includes H-2A(I-A) and H-2E(I-E) subclasses, and the non-classical MHC class II (MHC-IIb) comprises H-2M and H-2O. H-2K, H-2D, and H-2L are 80 to 90% homologous at the amino acid level yet appear to be involved in different recognition reactions and are differentially expressed on lymphoid cells. Class I MHC proteins bind antigenic peptide fragments and present them to CD8+ T lymphocytes. Class I molecules consist of a transmembrane alpha chain and a small chain called the beta-2-microglobulin. The alpha chain contains three extracellular domains, two of which fold together to form the peptide-binding cleft (alpha1 and alpha2), and one which has an Ig fold (alpha3). Peptide binding to class I molecules occurs in the endoplasmic reticulum (ER) and involves both chaperones and dedicated factors to assist in peptide loading. Class I MHC molecules are expressed on most nucleated cells.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 1622857065 150 GTVSVVCLLNNFYPREASVKWKVDGVLKTgNSQESVTEQDSKDNTYSLSSTLTLSSTDYQShnvYACEVTHQGLSSPVT 228
Cdd:cd21020    18 GDVTLRCWALGFYPADITLTWQLNGEELT-QEMELVETRPAGDGTFQKWASVVVPLGKEQK---YTCHVEHEGLPEPLT 92

Signal-regulatory protein (SIRP) immunoglobulin-like domain 3; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig)-like domain in Signal-Regulatory Protein (SIRP), domain 3 (C1 repeat 2). 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 that 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, but with much less affinity.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1622857065 152 VSVVCLLNNFYPREASVKWkvdgvLKTGNsqESVTEQDS-----KDNTYSLSSTLTLSSTDYQSHNVYACEVTHQGlSSP 226
Cdd:cd16085    18 VNVTCQVEKFYPQRLQLTW-----LENGN--VSRTETPStltvnKDGTYNWTSWLLVNVSAHREDVVLTCQVEHDG-QPA 89

                  ....
gi 1622857065 227 VTKS 230
Cdd:cd16085    90 VTKN 93

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DR; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DR. HLA-DR is an MHC class II cell surface receptor encoded by the human leukocyte antigen complex on chromosome 6 region 6p21.31. HLA-DR is also involved in several autoimmune conditions, disease susceptibility, and disease resistance including seronegative-rheumatoid arthritis, penicillamine-induced myasthenia, schizophrenia, Goodpasture syndrome, systemic lupus erythematosus, Alzheimers, tuberculoid leprosy, and Hashimoto's thyroiditis. HLA-DR molecules are upregulated in response to signaling. HLA-DR is an alphabeta heterodimer cell surface receptor, each subunit of which contains two extracellular domains, a membrane-spanning domain, and a cytoplasmic tail. Both alpha and beta chains are anchored in the membrane. The DR beta chain is encoded by 4 loci, however no more than 3 functional loci are present in a single individual, and no more than two on a single chromosome. Sometimes an individual may only possess 2 copies of the same locus, DRB1*. The HLA-DRB1 locus is ubiquitous and encodes a very large number of functionally variable gene products (HLA-DR1 to HLA-DR17). The HLA-DRB3 locus encodes the HLA-DR52 specificity, is moderately variable and is variably associated with certain HLA-DRB1 types. The HLA-DRB4 locus encodes the HLA-DR53 specificity, has some variation, and is associated with certain HLA-DRB1 types. The HLA-DRB5 locus encodes the HLA-DR51 specificity, which is typically invariable, and is linked to the HLA-DR2 types. Three genetically distinct isotypes of class II MHC molecules are found in humans (HLA-DR, HLA-DQ, and HLA-DP), and two in mice (I-E and I-A). MHC class II molecules play a key role in the initiation of the antigen-specific immune reponse. These molecules have been shown to be expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice. The expression of these molecules has been shown to be induced in nonprofessional APCs such as keratinocyctes, and they are expressed on the surface of activated human T cells and on T cells from other species. The MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes. These peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC. These peptides bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1622857065 135 PSVFIFPpSEDQVTSGTVSVVCLLNNFYPREASVKW------KVDGVLKTGNSQESvteqdskDNTYSLSSTLTLSStdy 208
Cdd:cd21000     4 PKVTVYP-AKTQPLQHHNLLVCSVNGFYPGSIEVRWfrngqeEKAGVVSTGLIQNG-------DWTFQTLVMLETVP--- 72

                          90       100
                  ....*....|....*....|
gi 1622857065 209 QSHNVYACEVTHQGLSSPVT 228
Cdd:cd21000    73 RSGEVYTCQVEHPSVTSPLT 92

CH1 domain (first constant Ig domain of the heavy chain) in immunoglobulin heavy epsilon and gamma 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 epsilon and gamma 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        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1622857065 134 APSVFIFPPSEDQVTSGTVSVVCLLNNFYPREASVKWKVDGVLKTGNSQESVTEQdskDNTYSLSSTLTLSSTDYQSHNv 213
Cdd:cd21817     1 APSVFPLAPCCKSTNGSSVTLGCLVTGYFPEPVTVTWNSGSLTSGVKTFPAVLQS---SGLYTTSSQVTVPSSSWGSQT- 76

                          90
                  ....*....|....*.
gi 1622857065 214 YACEVTHQGLSSPVTK 229
Cdd:cd21817    77 FTCNVEHKPSSTKVDK 92

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of T10, T22, and similar proteins; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class Ib major histocompatibility complex (MHC) immunoglobulin domain of the murine H-2T-encoded T10, T22, and similar proteins. T10 and T22 are highly related nonclassical major histocompatibility complex (MHC) class Ib proteins that bind to certain gammadelta T cell receptors (TCRs) in the absence of other components. Classical MHC class I (class Ia) molecules participate in immune responses by presenting peptide antigens to cytolytic alpha beta T cells. Many nonclassical MHC class I (class Ib) molecules have distinct antigen-binding capabilities, suggesting that they have evolved for specific tasks that are distinct from those of MHC class Ia. Members of the IgC family are components of immunoglobulin, T-cell receptors, CD1 cell surface glycoproteins, secretory glycoproteins A/C, and major histocompatibility complex (MHC) class I/II molecules. In immunoglobulins, each chain is composed of one variable domain (IgV) and one or more IgC domains. These names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. The IgV domain is responsible for antigen binding, and the IgC domain is involved in oligomerization and molecular interactions.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 1622857065 150 GTVSVVCLLNNFYPREASVKWKVDGVLKTgNSQESVTEQDSKDNTYSLSSTLTLSSTDYQShnvYACEVTHQGLSSPVT 228
Cdd:cd21016    18 GDVTLRCWALGFYPADITLTWQKDGEELT-QDMEFVETRPAGDGTFQKWAAVVVPLGKEQS---YTCHVYHEGLPEPLT 92

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of Qa-2; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class Ib major histocompatibility complex (MHC) immunoglobulin domain of QA-2. Qa-2 is a nonclassical MHC Ib antigen, which has been implicated in both innate and adaptive immune responses, as well as embryonic development. Qa-2 has an unusual peptide binding specificity in that it requires two dominant C-terminal anchor residues and is capable of associating with a substantially more diverse array of peptide sequences than other nonclassical MHC. Class I MHC proteins bind antigenic peptide fragments and present them to CD8+ T lymphocytes. Class I molecules consist of a transmembrane alpha chain and a small chain called the beta-2-microglobulin. The alpha chain contains three extracellular domains, two of which fold together to form the peptide-binding cleft (alpha1 and alpha2), and one which has an Ig fold (alpha3). Peptide binding to class I molecules occurs in the endoplasmic reticulum (ER) and involves both chaperones and dedicated factors to assist in peptide loading. Class I MHC molecules are expressed on most nucleated cells.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 1622857065 150 GTVSVVCLLNNFYPREASVKWKVDGVLKTgNSQESVTEQDSKDNTYSLSSTLTLSSTDYQShnvYACEVTHQGLSSPVT 228
Cdd:cd21014    17 GAVTLRCWALGFYPADITLTWQLNGEELT-QDMELVETRPAGDGTFQKWASVVVPLGKEQN---YTCHVNHEGLPEPLT 91

Immunoglobulin domain of Zn-alpha2-glycoprotein (ZAG); member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin domain of Zn-alpha2-glycoprotein (ZAG). ZAG is a soluble protein that is present in serum and other body fluids. ZAG stimulates lipid degradation in adipocytes and causes the extensive fat losses associated with some advanced cancers. The 2.8 angstrom crystal structure of ZAG resembles a class I major histocompatibility complex (MHC) heavy chain, but ZAG does not bind the class I light chain beta-2-microglobulin. The ZAG structure includes a large groove analogous to class I MHC peptide binding grooves. Instead of a peptide, the ZAG groove contains a nonpeptidic compound that may be implicated in lipid catabolism under normal or pathological conditions. IgC_MHC_I_alpha3; Immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class I alpha chain. Class I MHC proteins bind antigenic peptide fragments and present them to CD8+ T lymphocytes. Class I molecules consist of a transmembrane alpha chain and a small chain called the beta-2-microglobulin. The alpha chain contains three extracellular domains, two of which fold together to form the peptide-binding cleft (alpha1 and alpha2), and one which has an Ig fold (alpha3). Peptide binding to class I molecules occurs in the endoplasmic reticulum (ER) and involves both chaperones and dedicated factors to assist in peptide loading. Class I MHC molecules are expressed on most nucleated cells.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1622857065 133 AAPSVFIfppSEDQVTSGTVSVVCLLNNFYPREASVKWKvdgvlKTGNSQESVTEQD---SKDNTYSLSSTLTLSSTDYQ 209
Cdd:cd21010     3 DPPSVSV---TSHVAPGKNRTLKCLAYDFYPRGISLHWT-----RAGKVQESESGGDvlpSGNGTYQSWVVVEVPPQDRA 74

                          90
                  ....*....|....*....
gi 1622857065 210 ShnvYACEVTHQGLSSPVT 228
Cdd:cd21010    75 P---YSCHVEHSSLAQPLT 90

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 1622857065  28 QSPSSLSASAGDRVTITCRASQGISTYLN------WYQQKPGKAPKRLIyAASSLESGVP------SRFSGSGSGTDFTL 95
Cdd:cd05712     4 QMPKSVTVQEGLCVLIPCSFSYPADYWVSnpvhgyWYRGGPYPKYRPPV-ATNNRTREVHestqgrFRLLGDPGKKNCSL 82

                          90
                  ....*....|....
gi 1622857065  96 TISSLQPEDFATYY 109
Cdd:cd05712    83 SISDARPEDSGKYF 96

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 1622857065  37 AGDRVTITCRAS--QGISTYLNWYQQKPGKAPKRL--IYAASSLESGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCLQ 112
Cdd:cd16095    14 AGKTLSLKCQTSgfQFNTSQLSWYLWVPGHAPLWLtsLDHISTKVSEDRITSSREDTNSQIFLQIKGLGLRDSGQYHCAR 93

                          90       100
                  ....*....|....*....|.
gi 1622857065 113 Y-----NSNPFTFGPGTKLDI 128
Cdd:cd16095    94 RvgygdDTDKLIFGPGTDVIV 114