1ymm
From Proteopedia
TCR/HLA-DR2b/MBP-peptide complex
Structural highlights
FunctionDRA_HUMAN Binds peptides derived from antigens that access the endocytic route of antigen presenting cells (APC) and presents them on the cell surface for recognition by the CD4 T-cells. The peptide binding cleft accommodates peptides of 10-30 residues. The peptides presented by MHC class II molecules are generated mostly by degradation of proteins that access the endocytic route, where they are processed by lysosomal proteases and other hydrolases. Exogenous antigens that have been endocytosed by the APC are thus readily available for presentation via MHC II molecules, and for this reason this antigen presentation pathway is usually referred to as exogenous. As membrane proteins on their way to degradation in lysosomes as part of their normal turn-over are also contained in the endosomal/lysosomal compartments, exogenous antigens must compete with those derived from endogenous components. Autophagy is also a source of endogenous peptides, autophagosomes constitutively fuse with MHC class II loading compartments. In addition to APCs, other cells of the gastrointestinal tract, such as epithelial cells, express MHC class II molecules and CD74 and act as APCs, which is an unusual trait of the GI tract. To produce a MHC class II molecule that presents an antigen, three MHC class II molecules (heterodimers of an alpha and a beta chain) associate with a CD74 trimer in the ER to form a heterononamer. Soon after the entry of this complex into the endosomal/lysosomal system where antigen processing occurs, CD74 undergoes a sequential degradation by various proteases, including CTSS and CTSL, leaving a small fragment termed CLIP (class-II-associated invariant chain peptide). The removal of CLIP is facilitated by HLA-DM via direct binding to the alpha-beta-CLIP complex so that CLIP is released. HLA-DM stabilizes MHC class II molecules until primary high affinity antigenic peptides are bound. The MHC II molecule bound to a peptide is then transported to the cell membrane surface. In B-cells, the interaction between HLA-DM and MHC class II molecules is regulated by HLA-DO. Primary dendritic cells (DCs) also to express HLA-DO. Lysosomal miroenvironment has been implicated in the regulation of antigen loading into MHC II molecules, increased acidification produces increased proteolysis and efficient peptide loading. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedAutoimmune diseases are caused by self-reactive lymphocytes that have escaped deletion. Here we have determined the structure of the trimolecular complex for a T cell receptor (TCR) from a patient with multiple sclerosis that causes autoimmunity in transgenic mice. The structure showed a TCR topology notably different from that of antimicrobial TCRs. Rather than being centered on the peptide-major histocompatibility complex, this TCR contacted only the N-terminal peptide segment and made asymmetrical interactions with the major histocompatibility complex helices. The interaction was dominated by the hypervariable complementarity-determining region 3 loops, indicating that unconventional topologies are possible because of the unique complementarity-determining region 3 sequences created during rearrangement. This topology reduces the interaction surface with peptide and alters the geometry for CD4 association. We propose that unusual TCR-binding properties can permit autoreactive T cells to escape deletion. Unconventional topology of self peptide-major histocompatibility complex binding by a human autoimmune T cell receptor.,Hahn M, Nicholson MJ, Pyrdol J, Wucherpfennig KW Nat Immunol. 2005 May;6(5):490-6. Epub 2005 Apr 10. PMID:15821740[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
| ||||||||||||||||||||
