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 189524728   21 QPQNAAVLQGSSAQFNC--SSTQPPQImTFMLNGRlvvtimqtsgVLNSTDRFSASNftTPGNYKwqFTISNVQRSDAGV 98
Cdd:pfam07679   6 KPKDVEVQEGESARFTCtvTGTPDPEV-SWFKDGQ----------PLRSSDRFKVTY--EGGTYT--LTISNVQPDDSGK 70

                          90       100
                  ....*....|....*....|
gi 189524728   99 VACQV---LGGDAVTATLSV 115
Cdd:pfam07679  71 YTCVAtnsAGEAEASAELTV 90

Immunoglobulin I-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 189524728   21 QPQNAAVLQGSSAQFNC--SSTQPPQImTFMLNGRlvvtimqtsgVLNSTDRFSASNftTPGNYKwqFTISNVQRSDAGV 98
Cdd:pfam07679   6 KPKDVEVQEGESARFTCtvTGTPDPEV-SWFKDGQ----------PLRSSDRFKVTY--EGGTYT--LTISNVQPDDSGK 70

                          90       100
                  ....*....|....*....|
gi 189524728   99 VACQV---LGGDAVTATLSV 115
Cdd:pfam07679  71 YTCVAtnsAGEAEASAELTV 90

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 189524728    22 PQNAAVLQGSSAQFNCSSTQPPQIMTFMLNGRLVVtimqtsgvLNSTDRFSASNfttpGNYKWQFTISNVQRSDAGVVAC 101
Cdd:smart00410   1 PPSVTVKEGESVTLSCEASGSPPPEVTWYKQGGKL--------LAESGRFSVSR----SGSTSTLTISNVTPEDSGTYTC 68

                           90
                   ....*....|....*..
gi 189524728   102 QV---LGGDAVTATLSV 115
Cdd:smart00410  69 AAtnsSGSASSGTTLTV 85

Immunoglobulin constant (IgC)-like domain of antigen receptor Cluster of Differentiation (CD) 80; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin constant (IgC)-like domain of the antigen receptor Cluster of Differentiation (CD) 80. CD80 (also known as glycoprotein B7-1) and CD86 (also known as glycoprotein B7-2) are expressed on antigen-presenting cells and deliver the co-stimulatory signal through CD28 and CTLA-4 (CD152) on T cells. signaling through CD28 augments the T-cell response, whereas CTLA-4 signaling attenuates it. CD80 contains two Ig-like domains, an amino-terminal immunoglobulin variable (IgV)-like domain characteristic of adhesion molecules, and a membrane proximal immunoglobulin constant (IgC)-like domain similar to the constant domains of antigen receptors. Members of the Ig 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
                 ....*....|....*....|....*....|....*....|....*....|....*.
gi 189524728 140 CLAAGWYPEPNMSWSVNGETQFCNKSSVTQ---GGLYNSSCTLTLTASKNSTVQCL 192
Cdd:cd16083   21 CSTSGGFPEPRLSWLENGEELNAINTTVSQdpeTELYTVSSELDFNVTYNHSIVCL 76

Immunoglobulin I-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 189524728   21 QPQNAAVLQGSSAQFNC--SSTQPPQImTFMLNGRlvvtimqtsgVLNSTDRFSASNftTPGNYKwqFTISNVQRSDAGV 98
Cdd:pfam07679   6 KPKDVEVQEGESARFTCtvTGTPDPEV-SWFKDGQ----------PLRSSDRFKVTY--EGGTYT--LTISNVQPDDSGK 70

                          90       100
                  ....*....|....*....|
gi 189524728   99 VACQV---LGGDAVTATLSV 115
Cdd:pfam07679  71 YTCVAtnsAGEAEASAELTV 90

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 189524728    22 PQNAAVLQGSSAQFNCSSTQPPQIMTFMLNGRLVVtimqtsgvLNSTDRFSASNfttpGNYKWQFTISNVQRSDAGVVAC 101
Cdd:smart00410   1 PPSVTVKEGESVTLSCEASGSPPPEVTWYKQGGKL--------LAESGRFSVSR----SGSTSTLTISNVTPEDSGTYTC 68

                           90
                   ....*....|....*..
gi 189524728   102 QV---LGGDAVTATLSV 115
Cdd:smart00410  69 AAtnsSGSASSGTTLTV 85

Immunoglobulin (Ig)-like domain of human titin C terminus and similar proteins; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the fifth immunoglobulin (Ig)-like domain from the C-terminus of human titin x and similar proteins. Titin (also called connectin) is a fibrous sarcomeric protein specifically found in vertebrate striated muscle. Titin is gigantic; depending on isoform composition it ranges from 2970 to 3700 kDa, and is of a length that spans half a sarcomere. Titin largely consists of multiple repeats of Ig-like and fibronectin type 3 (FN-III)-like domains. Titin connects the ends of myosin thick filaments to Z disks and extends along the thick filament to the H zone and appears to function similar to an elastic band, keeping the myosin filaments centered in the sarcomere during muscle contraction or stretching. This group belongs to the I-set of IgSF domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. 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
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 189524728  21 QPQNAAVLQGSSAQFNCSST-QPPQIMTFMLNGRLVVTimqtsgvlnstdrfSASNFTTPGNYKWQFTISNVQRSDAG 97
Cdd:cd05747    9 KPRSLTVSEGESARFSCDVDgEPAPTVTWMREGQIIVS--------------SQRHQITSTEYKSTFEISKVQMSDEG 72

agrin-responsive first immunoglobulin-like domains (Ig1) of the MuSK ectodomain; a member of the I-set of IgSF domains; The members here are composed of the first immunoglobulin-like domains (Ig1) of the Muscle-specific kinase (MuSK). MuSK is a receptor tyrosine kinase specifically expressed in skeletal muscle, where it plays a central role in the formation and maintenance of the neuromuscular junction (NMJ). MuSK is activated by agrin, a neuron-derived heparan sulfate proteoglycan. The activation of MUSK in myotubes regulates the formation of NMJs through the regulation of different processes including the specific expression of genes in subsynaptic nuclei, the reorganization of the actin cytoskeleton and the clustering of the acetylcholine receptors (AChR) in the postsynaptic membrane. The Ig superfamily (IgSF) is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. 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. Unlike the V-set, one of the distinctive features of I-set domains is the lack of a C" strand. The structure of the MuSK lacks this strand and thus it belongs to the I-set of the IgSF. I-set domains are found in several cell adhesion molecules (such as VCAM, ICAM, and MADCAM), and are also present in numerous other diverse protein families, including several tyrosine-protein kinase receptors, the hemolymph protein hemolin, the muscle proteins titin, telokin, and twitchin, the neuronal adhesion molecule axonin-1, and the signaling molecule semaphorin 4D that is involved in axonal guidance, immune function and angiogenesis.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 189524728  17 SADLQPQNAAVLQGSSAQFNCSSTQPPQ-IMTFMLNGRLVVTImqtsgvlNSTDRFSASNFTtpgnykwqFTISNVQRSD 95
Cdd:cd20970    4 STPQPSFTVTAREGENATFMCRAEGSPEpEISWTRNGNLIIEF-------NTRYIVRENGTT--------LTIRNIRRSD 68

                         90       100
                 ....*....|....*....|....*...
gi 189524728  96 AGVVACQVLGGdavtATLSVQDRGTVQI 123
Cdd:cd20970   69 MGIYLCIASNG----VPGSVEKRITLQV 92

Immunoglobulin domain; Members of the immunoglobulin superfamily are found in hundreds of proteins of different functions. Examples include antibodies, the giant muscle kinase titin and receptor tyrosine kinases. Immunoglobulin-like domains may be involved in protein-protein and protein-ligand interactions.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 189524728   22 PQNAAVLQGSSAQFNCSST--QPPQIMTFMLNGRLVVTIMQTsgVLNSTDRFSASnfttpgnykwqFTISNVQRSDAGVV 99
Cdd:pfam00047   3 PPTVTVLEGDSATLTCSAStgSPGPDVTWSKEGGTLIESLKV--KHDNGRTTQSS-----------LLISNVTKEDAGTY 69

                  ....
gi 189524728  100 ACQV 103
Cdd:pfam00047  70 TCVV 73

CH1 domain (first constant Ig domain of the heavy chain) in immunoglobulin heavy alpha 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 alpha chains. It belongs to a family composed of the first immunoglobulin constant-1 set domain of alpha, 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
                 ....*....|....*....|....*....|....*....|....*....|....*..
gi 189524728 140 CLAAGWYPEP-NMSWSVNGE--TQFCNKSSVTQGGLYNSSCTLTLTAsknstVQCLA 193
Cdd:cd21818   22 CLVQGFFPEPvNVTWNYSGKggTARNFPAMLASGGRYTQSSQLTLPA-----DQCPE 73