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 9507239   22 VLHQPPAMSSALGTTIRLTCTLRNDhDIGVYSVYWYQQRPGHPPRFLLRYfsqsDKSQGPQVPPRFSGSKDvaRNRGYLS 101
Cdd:cd04984   1 VLTQPSSLSVSPGETVTITCTGSSG-NISGNYVNWYQQKPGSAPRYLIYE----DKHRPSGIPDRFSGSKS--GNTASLT 73

                        90
                ....*....|....*..
gi 9507239  102 ISELQPEDEAMYYCAMG 118
Cdd:cd04984  74 ISGAQTEDEADYYCQVW 90

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 9507239   22 VLHQPPAMSSALGTTIRLTCTLRNDhDIGVYSVYWYQQRPGHPPRFLLRYfsqsDKSQGPQVPPRFSGSKDvaRNRGYLS 101
Cdd:cd04984   1 VLTQPSSLSVSPGETVTITCTGSSG-NISGNYVNWYQQKPGSAPRYLIYE----DKHRPSGIPDRFSGSKS--GNTASLT 73

                        90
                ....*....|....*..
gi 9507239  102 ISELQPEDEAMYYCAMG 118
Cdd:cd04984  74 ISGAQTEDEADYYCQVW 90

Immunoglobulin V-Type;

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 9507239      36 TIRLTCTLRNDhDIGVYSVYWYQQRPGHPPRFLLRYFSQSDKSQGPQVPPRFSGSKDVARNRGYLSISELQPEDEAMYYC 115
Cdd:smart00406   1 SVTLSCKFSGS-TFSSYYVSWVRQPPGKGLEWLGYIGSNGSSYYQESYKGRFTISKDTSKNDVSLTISNLRVEDTGTYYC 79

                   .
gi 9507239     116 A 116
Cdd:smart00406  80 A 80

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 9507239   22 VLHQPPAMSSALGTTIRLTCTLRNDhDIGVYSVYWYQQRPGHPPRFLLRYfsqsDKSQGPQVPPRFSGSKDvaRNRGYLS 101
Cdd:cd04984   1 VLTQPSSLSVSPGETVTITCTGSSG-NISGNYVNWYQQKPGSAPRYLIYE----DKHRPSGIPDRFSGSKS--GNTASLT 73

                        90
                ....*....|....*..
gi 9507239  102 ISELQPEDEAMYYCAMG 118
Cdd:cd04984  74 ISGAQTEDEADYYCQVW 90

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 9507239   23 LHQPPA-MSSALGTTIRLTCTLRNDhdIGVYSVYWYQQRPGHPPRFLLRYFSQSDKSQGpQVPPRFSGSKDvARNRGYLS 101
Cdd:cd00099   1 VTQSPRsLSVQEGESVTLSCEVSSS--FSSTYIYWYRQKPGQGPEFLIYLSSSKGKTKG-GVPGRFSGSRD-GTSSFSLT 76

                        90       100
                ....*....|....*....|.
gi 9507239  102 ISELQPEDEAMYYCAMGARSS 122
Cdd:cd00099  77 ISNLQPEDSGTYYCAVSESGG 97

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 9507239   42 TLRNDHDIGVYSVYWYQQRPGHPPRFLLRYFSQSDKSQGPQVPPRFSGSKdVARNRGYLSISELQPEDEAMYYCAMGARS 121
Cdd:cd05899  17 TLRCSQKSGHDNMYWYRQDPGKGLQLLFYSYGGGLNEEGDLPGDRFSASR-PSLTRSSLTIKSAEPEDSAVYLCASSLGG 95

                .
gi 9507239  122 S 122
Cdd:cd05899  96 G 96

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 9507239   26 PPAMSSALGTTIRLTCtlrNDHDIGVYSVYWYQQRPGHPPRFLLRYFSQSDKSQGPqvppRFSGSKDVARNRGYLSISEL 105
Cdd:cd04983   5 PQSLSVQEGENVTLNC---NYSTSTFYYLFWYRQYPGQGPQFLIYISSDSGNKKKG----RFSATLDKSRKSSSLHISAA 77

                        90
                ....*....|....*..
gi 9507239  106 QPEDEAMYYCAMGARSS 122
Cdd:cd04983  78 QLSDSAVYFCALSESGG 94

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 9507239   23 LHQPPAMSSALGTTIRLTCTLRNDhDIGVYSVYWYQQRPGHPPRFL-LRYFSQSDKSQGPQVPPRFSGSKDVARNRGYLS 101
Cdd:cd04981   2 LQESGPGLVKPGQSLKLSCKASGF-TFTSYGMGWVRQAPGKGLEWIgLIYPGGGDTYYADSFKGRFTITRDTSKSTAYLQ 80

                        90       100
                ....*....|....*....|.
gi 9507239  102 ISELQPEDEAMYYCAMGARSS 122
Cdd:cd04981  81 LNSLTSEDTAVYYCARGLGGY 101

Immunoglobulin (Ig) variable (V) domain of T-cell receptor (TCR) delta chain; The members here are composed of the immunoglobulin (Ig) variable (V) domain of the delta chain of gamma/delta T-cell receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes, and are heterodimers consisting of alpha and beta chains or gamma and delta chains. Each chain contains a variable (V) and a constant (C) region. The majority of T cells contain alpha/beta TCRs, but a small subset contain gamma/delta TCRs. Alpha/beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. Gamma/delta TCRs recognize intact protein antigens; they recognize protein antigens directly and without antigen processing, and MHC independently of the bound peptide. Gamma/delta T cells can also be stimulated by non-peptide antigens such as small phosphate- or amine-containing compounds. The variable domain of gamma/delta TCRs is responsible for antigen recognition and is located at the N-terminus of the receptor. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 9507239   27 PAMSSALGTTIRLTCTLRNDHDigVYSVYWYQQRPGHPPRFLLRyfsQSDKSQGpQVPPRFSGSKDVARNRGYLSISELQ 106
Cdd:cd07706   7 PDVSVQVGEEVTLNCRYETSWT--NYYLFWYKQLPSGEMTFLIR---QDSSEQN-AKSGRYSVNFQKAQKSISLTISALQ 80

                        90
                ....*....|....
gi 9507239  107 PEDEAMYYCAMGAR 120
Cdd:cd07706  81 LEDSAKYFCALSLP 94

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 9507239   26 PPAMSSALGTTIRLTCTLRNDHDIGVYsvyWYQQRPGHP--PRFLLrYFSQSdksQGPQVPP-----RFSGSKDvaRNRG 98
Cdd:cd05720   5 PRKRDAQLGQKVELVCEVLNSVPQGCS---WLFQPRGSApqPTFLL-YLSSS---NKTKWAEgldskRFSGSRS--GSSY 75

                        90
                ....*....|....*..
gi 9507239   99 YLSISELQPEDEAMYYC 115
Cdd:cd05720  76 VLTLKDFRKEDEGYYFC 92

Immunoglobulin (Ig)-like domain of protein zero (P0) and similar proteins; The members here are composed of the immunoglobulin (Ig) domain of protein zero (P0), a myelin membrane adhesion molecule. P0 accounts for over 50% of the total protein in peripheral nervous system (PNS) myelin. P0 is a single-pass transmembrane glycoprotein with a highly basic intracellular domain and an extracellular Ig domain. The extracellular domain of P0 (P0-ED) is similar to the Ig variable domain, carrying one acceptor sequence for N-linked glycosylation. P0 plays a role in membrane adhesion in the spiral wraps of the myelin sheath. The intracellular domain is thought to mediate membrane apposition of the cytoplasmic faces and may, through electrostatic interactions, interact directly with lipid headgroups. It is thought that homophilic interactions of the P0 extracellular domain mediate membrane juxtaposition in the extracellular space of PNS myelin. This group also contains the Ig domain of sodium channel subunit beta-2 (SCN2B), and of epithelial V-like antigen 1 (EVA). EVA, also known as myelin protein zero-like 2, is an adhesion molecule, which may play a role in structural organization of the thymus and early lymphocyte development. SCN2B subunits play a role in determining sodium channel density and function in neurons,and in control of electrical excitability in the brain.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 9507239   26 PPAMSSALGTTIRLTCTLRNDHDIG-VYSVYWYQQRPGHPPRFLLRYFSQSDKSQGPqvPPRF----SGSKDVARNRGYL 100
Cdd:cd05715   6 PRELNVLNGSDVRLTCTFTSCYTVGdAFSVTWTYQPEGGNTTESMFHYSKGKPYILK--VGRFkdrvSWAGNPSKKDASI 83

                        90
                ....*....|....*
gi 9507239  101 SISELQPEDEAMYYC 115
Cdd:cd05715  84 VISNLQFSDNGTYTC 98