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 157817290  205 LGSSVSLPCRFSMAPGLDLTGVEWRLQHKGSGQ--LVYSWKTGQGQAKRKGATlKPEKLLRAGDASLTLPNLTLKDEGNY 282
Cdd:pfam07686  10 LGGSVTLPCTYSSSMSEASTSVYWYRQPPGKGPtfLIAYYSNGSEEGVKKGRF-SGRGDPSNGDGSLTIQNLTLSDSGTY 88

                          90       100
                  ....*....|....*....|.
gi 157817290  283 ICQISTSLYQ-AQQIVPLNIL 302
Cdd:pfam07686  89 TCAVIPSGEGvFGKGTRLTVL 109

Immunoglobulin C-Type;

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 157817290   319 SLICSIAGYYPLDVVVTWIReelGGIPAQvSGASFSSLRQNMMGTYSISSTVT---AEPGPtGATYTCQVAHVSLEEP 393
Cdd:smart00407   3 TLVCLVSGFYPPDITVTWLR---NGQEVT-EGVSTTDPLKNSDGTYFLSSYLTvpaSTWES-GDVYTCQVTHEGLKEP 75

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 157817290  205 LGSSVSLPCRFSMAPGLDLTGVEWRLQHKGSGQ--LVYSWKTGQGQAKRKGATlKPEKLLRAGDASLTLPNLTLKDEGNY 282
Cdd:pfam07686  10 LGGSVTLPCTYSSSMSEASTSVYWYRQPPGKGPtfLIAYYSNGSEEGVKKGRF-SGRGDPSNGDGSLTIQNLTLSDSGTY 88

                          90       100
                  ....*....|....*....|.
gi 157817290  283 ICQISTSLYQ-AQQIVPLNIL 302
Cdd:pfam07686  89 TCAVIPSGEGvFGKGTRLTVL 109

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 157817290   205 LGSSVSLPCRFSmapgldltgvewrlqhkGSGQLVYSWKTGQGQ--AKRKGATLKPEKllraGDASLTLPNLTLKDEGNY 282
Cdd:smart00410   8 EGESVTLSCEAS-----------------GSPPPEVTWYKQGGKllAESGRFSVSRSG----STSTLTISNVTPEDSGTY 66

                           90
                   ....*....|....*....
gi 157817290   283 ICQISTSLYQAQQIVPLNI 301
Cdd:smart00410  67 TCAATNSSGSASSGTTLTV 85

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 157817290 302 LASPKVQLILANKdplPSLICSIAGYYPLDVVVTWIReelGGIPAQVSGASFSSLRQNMmGTYSISS--TVTAEPGPTGA 379
Cdd:cd00098    4 LLPPSPEEKGGGK---VTLVCLVSGFYPKDITVTWLK---NGVPLTSGVSTSSPVEPND-GTYSVTSslTVPPSDWDEGA 76

                         90
                 ....*....|....*....
gi 157817290 380 TYTCQVAHVSLEEPLTVSM 398
Cdd:cd00098   77 TYTCVVTHESLKSPLSKTW 95

Immunoglobulin domain of Cluster of Differentiation (CD) 1; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin domain of Cluster of Differentiation (CD) 1. CD1 family of transmembrane glycoproteins, are structurally related to the major histocompatibility complex (MHC) proteins and form heterodimers with beta-2-microglobulin. They mediate the presentation of primarily lipid and glycolipid antigens of self or microbial origin to T cells. The human genome contains five CD1 family genes (CD1a, CD1b, CD1c, CD1d, and CD1e) organized in a cluster on chromosome 1. The CD1 family members are thought to differ in their cellular localization and specificity for particular lipid ligands. CD1a localizes to the plasma membrane and to recycling vesicles of the early endocytic system. Alternative splicing results in multiple transcript variants. 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. C1-set Ig domains 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 157817290 304 SPKVQLIlANKDPLPS---LICSIAGYYPLDVVVTWIREElggiPAQVSGASFSSLRQNMMGTYSISSTVTAEPGpTGAT 380
Cdd:cd21029    2 KPRVRLS-SRPSPGDGhlqLSCHVTGFYPRPIEVTWLRDG----QEQMDGTQSGGILPNHDGTYQLRKTLDIAPG-EGAG 75

                         90
                 ....*....|....*.
gi 157817290 381 YTCQVAHVSLEEPLTV 396
Cdd:cd21029   76 YSCRVDHSSLKQDLIV 91

Immunoglobulin C1-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 157817290  301 ILASPKVQLilanKDPlPSLICSIAGYYPLDVVVTWIReelGGIPAQvSGASFSSLRQNMMGTYSISS--TVTAEPGPTG 378
Cdd:pfam07654   3 VFPPSPEEL----GKP-NTLTCLVTGFYPPDITVTWLK---NGQEVT-EGVKTTPPSPNSDWTYQLSSylTVTPSDWESG 73

                          90
                  ....*....|..
gi 157817290  379 ATYTCQVAHVSL 390
Cdd:pfam07654  74 DEYTCRVEHEGL 85

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 157817290 305 PKVQLILANKDPLPS---LICSIAGYYPLDVVVTWIR---EELGGIpaqVSgasfSSLRQNmmGTYSISSTVTAEPGP-T 377
Cdd:cd21000    4 PKVTVYPAKTQPLQHhnlLVCSVNGFYPGSIEVRWFRngqEEKAGV---VS----TGLIQN--GDWTFQTLVMLETVPrS 74

                         90       100
                 ....*....|....*....|..
gi 157817290 378 GATYTCQVAHVSLEEPLTVSMR 399
Cdd:cd21000   75 GEVYTCQVEHPSVTSPLTVEWR 96

First immunoglobulin variable (IgV) domain of poliovirus receptor (PVR, also known as CD155 and necl-5), and similar domains; The members here are composed of the first immunoglobulin (Ig) domain of poliovirus receptor (PVR, also known as CD155 and nectin-like protein 5 (necl-5)). Poliovirus (PV) binds to its cellular receptor (PVR/CD155) to initiate infection. CD155 is a membrane-anchored, single-span glycoprotein; its extracellular region has three Ig-like domains. There are four different isotypes of CD155 (referred to as alpha, beta, gamma, and delta), that result from alternate splicing of the CD155 mRNA, and have identical extracellular domains. CD155-beta and CD155-gamma are secreted; CD155-alpha and CD155-delta are membrane-bound and function as PV receptors. The virus recognition site is contained in the amino-terminal domain, D1. Having the virus attachment site on the receptor distal from the plasma membrane may be important for successful initiation of infection of cells by the virus. CD155 binds in the poliovirus "canyon" with a footprint similar to that of the intercellular adhesion molecule-1 receptor on human rhinoviruses. This group also includes the first Ig-like domain of nectin-1 (also known as poliovirus receptor related protein(PVRL)1; CD111), nectin-3 (also known as PVRL 3), nectin-4 (also known as PVRL4; LNIR receptor)and DNAX accessory molecule 1 (DNAM-1; CD226).

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 157817290 186 VKTKVEFQVTAetqtlnqLLGSSVSLPCRFSMAPGLDLTGVEWRLQHKGSGQLVYSWKTGQG---QAKRKGATLKPEKLL 262
Cdd:cd05718    1 QRVQVPTEVTG-------FLGGSVTLPCSLTSPGTTKITQVTWMKIGAGSSQNVAVFHPQYGpsvPNPYAERVEFLAARL 73

                         90       100
                 ....*....|....*....|....*.
gi 157817290 263 RAGDASLTLPNLTLKDEGNYICQIST 288
Cdd:cd05718   74 GLRNATLRIRNLRVEDEGNYICEFAT 99

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DQ and I-A; 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 human histocompatibility antigen (HLA) DQ and mouse I-A. 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). I-A and I-E have the same basic features insofar as peptide loading and presentation, they differ in that each interacts with distinctly different sets of peptides, and in the incidence of deletion of their genes. A structural understanding of the similarities and differences between I-A and I-E may help with understanding their roles in peptide presentation and T cell activation. Mouse I-Ag7 has a genetic susceptibility to autoimmune diabetes due to its small, uncharged amino acid residue at position 57 of their beta chain which results in the absence of a salt bridge between beta 57 and Arg alpha 76, which is adjacent to the P9 pocket of the peptide-binding groove. Human HLA-DR, -DQ, and -DP are about 70% similar to each other. HLA-DQ (DQ) is a cell surface receptor protein found on antigen presenting cells. It is an alphabeta heterodimer of type MHC class II. The alpha and beta chains are encoded by two loci, HLA-DQA1 and HLA-DQB1, that are adjacent to each other on chromosome band 6p21.3. A person often produces two alpha-chain and two beta chain variants and thus 4 isoforms of DQ. HLA-DQ is involved in the autoimmune diseases celiac disease and diabetes mellitus type. DQ is one of several antigens involved in rejection of organ transplants. DQ2 is encoded by the HLA-DQB1*02 allele group. DQ6 is encoded by the HLA-DQB1*06 allele group. DQ2 beta-chains combine with alpha-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. These isoforms, nicknamed DQ2.2 and DQ2.5, are also encoded by the DQA1*0201 and DQA1*0501 genes, respectively. DQ6 beta-chains combine with alpha-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. For DQ6, however, cis-isoform pairing only occurs with DQ1 alpha-chains. There are many haplotypes of DQ6. Susceptibility to Leptospirosis infection was found associated with undifferentiated DQ6. DQ8 is determined by the antibody recognition of beta8 and this generally detects the gene product of DQB1*0302. DQ8 is commonly linked to autoimmune disease in the human population. DQ8 is the second most predominant isoform linked to celiac disease and the DQ most linked to Type 1 diabetes. DQ8 increases the risk for rheumatoid arthritis and is linked to the primary risk locus for RA, HLA-DR4. DR4 also plays an important role in Type 1 diabetes. DQ8 is a split antigen of the DQ3 broad antigen. MHC class II molecules play a key role in the initiation of the antigen-specific immune response. They are expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice, and induced in nonprofessional APCs, such as keratinocyctes; they are expressed on the surface of activated human T cells and on T cells from other species. 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, and 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 157817290 320 LICSIAGYYPLDVVVTWIR---EELGGIpaqVSgasfSSLRQNMMGTYSIssTVTAEPGPT-GATYTCQVAHVSLEEPLT 395
Cdd:cd21001   22 LVCSVTDFYPGQIKVRWFRndqEETAGV---VS----TPLIRNGDWTFQI--LVMLEMTPQrGDVYTCHVEHPSLQSPIT 92

                 ....
gi 157817290 396 VSMR 399
Cdd:cd21001   93 VEWR 96

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 157817290 301 ILASPKVQLILANKdplPSLICSIAGYYPLDVVVTWIReelGGIPAQVSGASFSSLRQNMMGTYSISS--TVTAEPGPTG 378
Cdd:cd05768    5 LLPPPEEELSLNET---VTLTCLVKGFYPEDIFVSWLQ---NGEPLPSADYKTTAPVPESDGSFFVYSklNVSTADWNSG 78

                         90
                 ....*....|....*...
gi 157817290 379 ATYTCQVAHVSLEEPLTV 396
Cdd:cd05768   79 DVFSCVVGHEALPLQFTQ 96

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) I-E; 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) I-E. 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). I-A and I-E molecules have the same basic features insofar as peptide loading and presentation, although each interacts with distinctly different sets of peptides. They also differ in that there is a relatively high incidence of deletion of the I-E gene in both inbred strains of mice as well as wild mice and the lack of the reverse situation i.e. the deletion of I-A genes. A detailed structural understanding of the similarities and differences between I-A and the paralogous I-E could help illuminate the respective roles these molecules play in peptide presentation and T cell activation. Mouse I-Ag7 has a genetic susceptibility to autoimmune diabetes due to its small, uncharged amino acid residue at position 57 of their beta chain which results in the absence of a salt bridge between beta 57 and Arg alpha 76, which is adjacent to the P9 pocket of the peptide-binding groove. 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 157817290 305 PKVQLILANKDPLPS---LICSIAGYYPLDVVVTWIR---EELGGIPAqvsgasfSSLRQNmmGTYSISSTVTAEPGP-T 377
Cdd:cd20998    7 PTVTVYPTKTQPLEHhnlLVCSVSDFYPGNIEVRWFRngkEEKTGIVS-------TGLVRN--GDWTFQTLVMLETVPqS 77

                         90       100
                 ....*....|....*....|..
gi 157817290 378 GATYTCQVAHVSLEEPLTVSMR 399
Cdd:cd20998   78 GEVYTCQVEHPSLTDPVTVEWK 99

Immunoglobulin (Ig)-like domain of myelin oligodendrocyte glycoprotein (MOG); The members here are composed of the immunoglobulin (Ig)-like domain of myelin oligodendrocyte glycoprotein (MOG). MOG, a minor component of the myelin sheath, is an important CNS-specific autoantigen, linked to the pathogenesis of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). It is a transmembrane protein having an extracellular Ig domain. MOG is expressed in the CNS on the outermost lamellae of the myelin sheath, and on the surface of oligodendrocytes, and may participate in the completion, compaction, and/or maintenance of myelin. This group also includes butyrophilin (BTN). BTN is the most abundant protein in bovine milk-fat globule membrane (MFGM).

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 157817290 192 FQVTAETQTLNQLLGSSVSLPCRFSmaPGLDLTGVEWRLQHKGSGQLVYSWKTGQGQAKR-----KGATlkpeKLLRA-- 264
Cdd:cd05713    1 FSVIGPTEPILALVGEDAELPCHLS--PKMSAEHMEVRWFRSQFSPVVHLYRDGQDQEEEqmpeyRGRT----ELLKDai 74

                         90       100       110
                 ....*....|....*....|....*....|....*....
gi 157817290 265 --GDASLTLPNLTLKDEGNYICQISTSLYQAQQIVPLNI 301
Cdd:cd05713   75 aeGSVALRIHNVRPSDEGQYTCFFRSGSFYEEATLELKV 113

Immunoglobulin Variable (IgV) domain of B7-H3, a member of the B7 family of immune checkpoint molecules; The members here are composed of the immunoglobulin variable (IgV) domain of B7-H3 also known as CD276), a member of the B7 family of immune checkpoint molecules. B7-H3 is an important immune checkpoint member of the B7 family and shares homology with other B7 ligands such as programmed death ligand 1 (PD-L1). The B7 family molecules interact with CD28 on T-cells to provide co-stimulatory signals that regulate T-cell activation and T-helper cell differentiation. Although B7-H3 has been shown to have both co-stimulatory and co-inhibitory effects on T-cell responses, the most current studies describe B7-H3 as a T cell inhibitor that promotes tumor aggressiveness and proliferation. Moreover, B7-H3 is highly overexpressed on a wide range of human solid cancers and promotes tumor growth, metastasis, and drug resistance. Thus, B7-H3 expression in tumors often correlates with both negative prognosis and poor clinical outcome in cancer patients. B7-H3 protein contains a predicted signal peptide, V- and C-like Ig domains (IgV and IgC), a transmembrane region, and an intracellular tail.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 157817290 204 LLGSSVSLPCRFSMAPGLDLTGVEWRLQHKGSGQLVYSWKTGQGQAKRKGA------TLKPEKLLRaGDASLTLPNLTLK 277
Cdd:cd20934   10 LVGTDATLRCSFSPEPGFSLAQLSVFWQLTDTKQLVHSFTESQDQGRDQGSayanrtALFPDLLAQ-GNASLRLQRVRVA 88

                         90
                 ....*....|
gi 157817290 278 DEGNYICQIS 287
Cdd:cd20934   89 DEGSYTCFVS 98

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DP; 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) DP. HLA class II histocompatibility antigen, DP(W2) beta chain is a protein that in humans is encoded by the HLA-DPB1 gene. It plays a central role in the immune system by presenting peptides derived from extracellular proteins. MHC class II molecules are encoded by three different loci, HLA-DR, -DQ, and -DP, which are about 70% similar to each other. HLA-DP is an alphabeta heterodimer cell-surface receptor. Each DP subunit (alpha-subunit, beta-subunit) is composed of a alpha-helical N-terminal domain, an IgG-like beta sheet, a membrane spanning domain, and a cytoplasmic domain. The alpha-helical domain forms the sides of the peptide binding groove. The beta sheet regions form the base of the binding groove and the bulk of the molecule as well as the inter-subunit (non-covalent) binding region. Individuals carrying the MHCII allele, HLA-DP2, are at risk for chronic beryllium disease (CBD), a debilitating inflammatory lung condition caused by the reaction of CD4 T cells to inhaled beryllium. 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 157817290 305 PKVQLILANKDPLPS---LICSIAGYYPLDVVVTWIR---EELGGIpaqVSgasfSSLRQNmmGTYSISSTVTAEPGP-T 377
Cdd:cd21003    4 PKVNVSPSKKGPLQHhnlLVCHVTDFYPGNIQVRWFLngqEETAGV---VS----TNLIHN--GDWTFQILVMLEMTPqQ 74

                         90       100
                 ....*....|....*....|..
gi 157817290 378 GATYTCQVAHVSLEEPLTVSMR 399
Cdd:cd21003   75 GDVYTCQVEHPSLDSPVTVEWK 96

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 157817290 200 TLNQLLGSSVSLPCRF-SMAPGLDLTGVEWRLQHKGSGQLVYSWKTGQGQAkrkgATLKP----EKLLRAG-----DASL 269
Cdd:cd05715    8 ELNVLNGSDVRLTCTFtSCYTVGDAFSVTWTYQPEGGNTTESMFHYSKGKP----YILKVgrfkDRVSWAGnpskkDASI 83

                         90
                 ....*....|....*..
gi 157817290 270 TLPNLTLKDEGNYICQI 286
Cdd:cd05715   84 VISNLQFSDNGTYTCDV 100

Class I major histocompatibility complex (MHC) alpha chain, alpha3 immunoglobulin domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the 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
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 157817290 320 LICSIAGYYPLDVVVTWIREELggipAQVSGASFSSLRQNMMGTYSISSTVTAEPGPTgATYTCQVAHVSLEEPLTV 396
Cdd:cd07698   19 LRCWALGFYPAEITLTWQRDGE----DQTQDMELVETRPNGDGTFQKWAAVVVPSGEE-QRYTCHVQHEGLPEPLTL 90

Immunoglobulin (Ig)-like domain of human cartilage link protein (LP), and similar domains; The members here are composed of the immunoglobulin (Ig)-like domain similar to that found in human cartilage link protein (LP; also called hyaluronan and proteoglycan link protein). In cartilage, chondroitin-keratan sulfate proteoglycan (CSPG), aggrecan, forms cartilage link protein stabilized aggregates with hyaluronan (HA). These aggregates contribute to the tissue's load bearing properties. Aggregates having other CSPGs substituting for aggrecan may contribute to the structural integrity of many different tissues. Members of the vertebrate HPLN (hyaluronan/HA and proteoglycan binding link) protein family are physically linked adjacent to CSPG genes.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 157817290 206 GSSVSLPCRFSMAPGLDLTG---VEWRLQHKGSGQL--VYSWktgQGQAKRKGATLKPEKLLRA---GDASLTLPNLTLK 277
Cdd:cd05877   12 GGNVTLPCRYHYEPELSAPRkirVKWTKLEVDYAKEedVLVA---IGTRHKSYGSYQGRVFLRRaddLDASLVITDLRLE 88

                         90       100
                 ....*....|....*....|....
gi 157817290 278 DEGNYICQISTSLYQAQQIVPLNI 301
Cdd:cd05877   89 DYGRYRCEVIDGLEDESVVVALRL 112

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
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|.
gi 157817290 319 SLICSIAGYYPLDVVVTWIREELGGipaqvSGASFSSLRQNmMGTYSISS--TVTAEPGPTgATYTCQVAH 387
Cdd:cd21817   20 TLGCLVTGYFPEPVTVTWNSGSLTS-----GVKTFPAVLQS-SGLYTTSSqvTVPSSSWGS-QTFTCNVEH 83

Immunoglobulin Variable (IgV) domain in HERV-H LTR-associating 2 (HHLA2); The members here are composed of the immunoglobulin variable (IgV) region in HERV-H LTR-associating 2 (HHLA2; also known as B7-H7/B7 homolog 7). HHLA2 is a member of the B7 family of immune regulatory proteins. Mature human HHLA2 consists of an extracellular domain (ECD) with three immunoglobulin-like domains, a transmembrane segment, and a cytoplasmic domain. HHLA2 is widely expressed in human cancers including non-small cell lung carcinoma (NSCLS), triple negative breast cancer (TNBC), and melanoma, but has limited expression on normal tissues. Interestingly, unlike other members of B7 family, HHLA2 is not expressed in mice or rats. HHLA2 functions as a T cell coinhibitory molecules as it inhibits the proliferation of activated CD4(+) and CD8(+) T cells and their cytokine production. Furthermore, HHLA2 is constitutively expressed on the surface of human monocytes and is induced on B cells after stimulation, however it is not inducible on T cells.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 157817290 204 LLGSSVSLPCRFSmaPGLDLTgVEWrlQHKGSGQLVYSWKTG------QGQAKRKGATLKPEKLLRaGDASLTLPNLTLK 277
Cdd:cd16091   10 LLSEDCILPCSFT--PGSEVV-IHW--YKQDSDIKVHSYYYGkdqlesQDQRYRNRTSLFKDQISN-GNASLLLRRVQLQ 83

                         90       100
                 ....*....|....*....|....
gi 157817290 278 DEGNYICQISTSLYQAQQIVPLNI 301
Cdd:cd16091   84 DEGRYKCYTSTIIGNQESFVNLKV 107

Immunoglobulin Variable (IgV) domain of Programmed death ligand 1 (PD-L1); The members here are composed of the immunoglobulin variable (IgV) domain of Programmed death ligand 1 (PD-L1; also known as Cluster of Differentiation 274 (CD274)). PD-L1 is a cell-surface ligand that competes with PD-L2 for binding to the immunosuppressive receptor programmed death-1 (PD-1). PD-1 is a member of the B7 family that plays an important role in negatively regulating immune responses upon interaction with its two ligands, PD-L1 or PD-L2. Like PD-L2, PD-L1 interacts with PD-1 and suppresses T cell proliferation and cytokine production. The PD-1 receptor is expressed on the surface of activated T cells, while PD-L1 is expressed on cancer cells. When PD-1 and PD-L1 bind together, they form a molecular shield protecting tumor cells from being destroyed by the immune system. Thus, inhibiting the binding of PD-L1 to PD-1 with an antibody leads to killing of tumor cells by T cells. PD-1 inhibitors (such as Pembrolizumab, Nivolumab, and Cemiplimab) and PD-L1 inhibitors (such as Atezolizumab, Avelumab, and Durvalumab ) are an emerging class of immunotherapy that stimulate lymphocytes against tumor cells.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 157817290 206 GSSVSLPCRFSMAPGLDLTG--VEWRLQHKGSGQLVYSWK--TGQGQAKRKGATLKPEKLLRaGDASLTLPNLTLKDEGN 281
Cdd:cd20947   13 GSNMTIECKFPVEKQLDLAAliVYWEMEDKNIIQFVHGEEdlKVQHSSYRQRARLLKDQLSL-GNAALQITDVKLQDAGV 91

                 ....*.
gi 157817290 282 YICQIS 287
Cdd:cd20947   92 YRCMIS 97

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen H; 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 human leukocyte antigen H (HLA-H). HLA-H (also known as hereditary hemochromatosis protein; HFE) is a major histocompatibility complex (MHC) class I-like protein that is mutated in Hereditary Hemochromatosis. HFE is a protein of 343 amino acids that includes a signal peptide, an extracellular transferrin receptor-binding region (a1 and a2), an immunoglobulin-like domain (a3), a transmembrane region, and a short cytoplasmic tail. HFE binds beta-2-microglobulin to form a heterodimer expressed at the cell surface. It binds transferrin receptor (TFRC) in its extracellular alpha1-alpha2 domain. HFE plays an important part in the regulation of hepcidin expression in response to iron overload and the liver is important in the pathophysiology of HFE-associated hemochromatosis. Nine HFE splicing variants have been reported with transcripts lacking exon 2 or exon 3, or exons 2-3, 2-4, or 2-5. Diverse mutations involving HFE introns and exons discovered in persons with hemochromatosis or their family members cause or probably cause high iron phenotypes. 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 157817290 294 QQIVPLnilaspkVQLILANKDPLPSLICSIAGYYPLDVVVTWIREELggiPAQVSGASFSSLRQNMMGTYSISSTVTAE 373
Cdd:cd21021    1 QQVPPL-------VKVTHHVTSSVTTLRCRALNYYPQNITMKWLKDKQ---PMDAKEFEPKDVLPNGDGTYQGWITLAVP 70

                         90       100
                 ....*....|....*....|...
gi 157817290 374 PGPTgATYTCQVAHVSLEEPLTV 396
Cdd:cd21021   71 PGEE-QRYTCQVEHPGLDQPLIV 92

Immunoglobulin (Ig)-like domain of the chondroitin sulfate proteoglycan core protein (CSPG), versican; The members here are composed of the immunoglobulin (Ig)-like domain of the chondroitin sulfate proteoglycan core protein (CSPG), versican. In CSPGs, the Ig-like domain is followed by hyaluronan (HA)-binding tandem repeats, and a C-terminal region with epidermal growth factor-like, lectin-like, and complement regulatory protein-like domains. Separating these N- and C-terminal regions is a nonhomologous glycosaminoglycan attachment region. In cartilage, the CSPG aggrecan (not included in this group) forms cartilage link protein stabilized aggregates with HA. These aggregates contribute to the tissue's load bearing properties. Like aggrecan, versican has a wide distribution in connective tissue and extracellular matrices. Aggregates having other CSPGs substituting for aggrecan may contribute to the structural integrity of many different tissues. Members of the vertebrate HPLN (hyaluronan/HA and proteoglycan binding link) protein family are physically linked adjacent to CSPG genes.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 157817290 205 LGSSVSLPCRFSMAPGL--------DLTGVEW-RLQ-------HKGSGQLVY---SWKTGQGQAKRKGATLKPEKLlraG 265
Cdd:cd05901   11 LSGSVVLPCRFSTLPTLppsynitsEFLRIKWtKIQvdkngkdHKETTVLVAqngIIKIGQEYMGRVSVPSHPEDQ---G 87

                         90       100       110
                 ....*....|....*....|....*....|....*.
gi 157817290 266 DASLTLPNLTLKDEGNYICQISTSLYQAQQIVPLNI 301
Cdd:cd05901   88 DASLTIVKLRASDAGVYRCEVMHGIEDTQDTVSLDV 123

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 157817290  204 LLGSSVSLPCRFSmaPGLDLTGVEWrlqhkgsgqlvysWKTGQGqakRKGATLKPEKLLRAGDASLTLPNLTLKDEGNYI 283
Cdd:pfam00047   9 LEGDSATLTCSAS--TGSPGPDVTW-------------SKEGGT---LIESLKVKHDNGRTTQSSLLISNVTKEDAGTYT 70

                  ....*..
gi 157817290  284 CQISTSL 290
Cdd:pfam00047  71 CVVNNPG 77

Class I major histocompatibility complex (MHC) beta-2-microglobulin; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin-like domain in beta-2-microglobulin (beta2m). Beta2m is the non-covalently bound light chain of the human class I major histocompatibility complex (MHC-I). Beta2m is structured as a beta-sandwich domain composed of two facing beta-sheets (four stranded and three stranded), that is typical of the C-type immunoglobulin superfamily. This structure is stabilized by an intramolecular disulfide bridge connecting two Cys residues in the facing beta-sheets. In vivo, MHC-I continuously exposes beta2m on the cell surface, where it may be released to plasmatic fluids, transported to the kidneys, degraded, and finally excreted.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 157817290 320 LICSIAGYYPLDVVvtwIREELGGIP---AQVSGASFSSlrqnmmgTYSISSTVTAEPGPT-GATYTCQVAHVSLEEPLT 395
Cdd:cd05770   21 LNCYVSGFHPPDIE---IRLLKNGVKiedVEQSDLSFSK-------DWTFYLLKYTEFTPTkGDEYACRVRHNTLSEPKI 90

                 ....
gi 157817290 396 VSMR 399
Cdd:cd05770   91 YKWD 94

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of Qa-1 and similar proteins; member of the C1-set of Ig superfamily (IgSF) domains; Class Ib major histocompatibility complex (MHC) immunoglobulin domain of Qa-1 and similar proteins. Qa-1 presents hydrophobic peptides including Qdm derived from the leader sequence of classical MHC I molecules for immune surveillance by NK cells. Qa-1 bound peptides derived from the TCR Vbeta8.2 of activated T cells also activates CD8+ regulatory T cells to control autoimmunity and maintain self-tolerance. Four allotypes of Qa-1 (Qa-1a-d) are expressed that are highly conserved in sequence but have several variations that could affect peptide binding to Qa-1 or TCR recognition. 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 157817290 319 SLICSIAGYYPLDVVVTWireELGGiPAQVSGASFSSLRQNMMGTYSISSTVTAEPGPTgATYTCQVAHVSLEEPLTV 396
Cdd:cd21013   20 TLRCWALGFYPADITLTW---QLNG-EELTQDMEFVETRPAGDGTFQKWASVVVPLGKE-QKYTCHVEHEGLPEPLTL 92

First immunoglobulin (Ig) variable (V) domain of rat MRC OX-2 antigen, and similar domains; The members here are composed of the first immunoglobulin (Ig) domain of rat MRC OX-2 antigen (also known as CD200) and similar proteins. MRC OX-2 is a membrane glycoprotein expressed in a variety of lymphoid and non-lymphoid cells in rats. It has a similar broad distribution pattern in humans. MRC OX-2 may regulate myeloid cell activity. The protein has an extracellular portion containing two Ig-like domains, a transmembrane portion, and a cytoplasmic portion.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 157817290 198 TQTLNQLLGSSVSLPCRFSMApgLDLTGVEW-RLQHKGSGQLV-YSWKTG---QGQAKRKgATLKPEKLlraGDASLTLP 272
Cdd:cd05846    5 TGDTRAVLGGNATLSCNLTLP--EEVLQVTWqKIKASSPENIVtYSKKYGvkiQPSYVRR-ISFTSSGL---NSTSITIW 78

                         90
                 ....*....|....*.
gi 157817290 273 NLTLKDEGNYICQIST 288
Cdd:cd05846   79 NVTLEDEGCYKCLFNT 94

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) G; 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 human leukocyte antigen (HLA) G. HLA-G histocompatibility antigen (also known as human leukocyte antigen G ; HLA-G) is a protein that in humans is encoded by the HLA-G gene. HLA-G belongs to the HLA nonclassical class I heavy chain paralogs. This class I molecule is a heterodimer consisting of a heavy chain and light chain, beta-2-microglobulin. The heavy chain is anchored in the membrane. HLA-G may play a role in immune tolerance in pregnancy, being expressed in the placenta by extravillous trophoblast cells (EVT), while the classical MHC class I genes (HLA-A and HLA-B) are not. Immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class I and class II. 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. MHC class II molecules play a key role in the initiation of the antigen-specific immune repose. 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
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 157817290 319 SLICSIAGYYPLDVVVTWIREElggiPAQVSGASFSSLRQNMMGTYSISSTVTAePGPTGATYTCQVAHVSLEEPLTV 396
Cdd:cd21022   20 TLRCWALGFYPAEIILTWQRDG----EDQTQDVELVETRPAGDGTFQKWAAVVV-PSGEEQRYTCHVQHEGLPEPLML 92

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) E; 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 human leukocyte antigen (HLA) E. HLA-E is the first human class Ib major histocompatibility complex molecule to be crystallized. Like other MHC class I molecules, HLA-E is a heterodimer consisting of an a heavy chain and light chain beta-2-microglobulin. HLA-E is highly conserved and almost nonpolymorphic, and has recently been shown to be the first specialized ligand for natural killer cell receptors. 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 157817290 319 SLICSIAGYYPLDVVVTWIREELGgipaQVSGASFSSLRQNMMGTYSISSTVTAEPGPTGAtYTCQVAHVSLEEPLTV 396
Cdd:cd21024   21 TLRCWALGFYPAEITLTWQQDGEG----HTQDTELVETRPAGDGTFQKWAAVVVPSGEEQR-YTCHVQHEGLPEPVTL 93

Class Ia major histocompatibility complex (MHC) immunoglobulin domain of H-2Kb; 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 H-2Kb. H-2Kb is an alloantigen for the 2C T cell receptor (TCR). H-2Kb forms a complex with beta-2-microglobulin, and a peptide, including VSV-8 (RGYVYNGL), SEV-9 (FAPGNYPAL), and OVA-8 (SIINFEKL). Comparison of the OVA-8, VSV-8, and SEV-9 complexes with H-2Kb indicates that four side chains (Lys-66, Glu-152, Arg-155, and Trp-167) adopt peptide-specific conformations. H-2Kb paralogs include H-2Db, H-2Kbml and H-2KbI1s. 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 157817290 319 SLICSIAGYYPLDVVVTWireELGGiPAQVSGASFSSLRQNMMGTYSISSTVTAEPGPTgATYTCQVAHVSLEEPLTV 396
Cdd:cd21019   20 TLRCWALGFYPADITLTW---QLNG-EELIQDMELVETRPAGDGTFQKWASVVVPLGKE-QYYTCHVYHQGLPEPLTL 92