6cqj
From Proteopedia
Crystal structure of DR1 presenting the RQ13 peptide
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. Publication Abstract from PubMedRare individuals, termed HIV controllers, spontaneously control HIV infection by mounting efficient T cell responses against the virus. Protective CD4(+) T cell responses from HIV controllers involve high-affinity public T cell receptors (TCRs) recognizing an immunodominant capsid epitope (Gag293) presented by a remarkably broad array of human leukocyte antigen (HLA) class II molecules. Here, we determine the structures of a prototypical public TCR bound to HLA-DR1, HLA-DR11, and HLA-DR15 molecules presenting the Gag293 epitope. TCR recognition was driven by contacts with the Gag293 epitope, a feature that underpinned the extensive HLA cross-restriction. These high-affinity TCRs promoted mature immunological synapse formation and cytotoxic capacity in both CD4(+) and CD8(+) T cells. The public TCRs suppressed HIV replication in multiple genetic backgrounds ex vivo, emphasizing the functional advantage conferred by broad HLA class II cross-restriction. CD4(+) T cell-mediated HLA class II cross-restriction in HIV controllers.,Galperin M, Farenc C, Mukhopadhyay M, Jayasinghe D, Decroos A, Benati D, Tan LL, Ciacchi L, Reid HH, Rossjohn J, Chakrabarti LA, Gras S Sci Immunol. 2018 Jun 8;3(24). pii: 3/24/eaat0687. doi:, 10.1126/sciimmunol.aat0687. PMID:29884618[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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