PathwayStep6612 PathwayStep6586 PathwayStep6571 Antigen processing: Ubiquitination & Proteasome degradation Class I MHC mediated antigen processing & presentation Authored: Garapati, P V, 2010-10-29 Edited: Garapati, P V, 2010-10-29 GENE ONTOLOGYGO:0002474 Major histocompatibility complex (MHC) class I molecules play an important role in cell mediated immunity by reporting on intracellular events such as viral infection, the presence of intracellular bacteria or tumor-associated antigens. They bind peptide fragments of these proteins and presenting them to CD8+ T cells at the cell surface. This enables cytotoxic T cells to identify and eliminate cells that are synthesizing abnormal or foreign proteins. MHC class I is a trimeric complex composed of a polymorphic heavy chain (HC or alpha chain) and an invariable light chain, known as beta2-microglobulin (B2M) plus an 8-10 residue peptide ligand. Represented here are the events in the biosynthesis of MHC class I molecules, including generation of antigenic peptides by the ubiquitin/26S-proteasome system, delivery of these peptides to the endoplasmic reticulum (ER), loading of peptides to MHC class I molecules and display of MHC class I complexes on the cell surface. Pubmed12495737 Pubmed17055423 Pubmed17145306 Pubmed18243674 Pubmed18641646 Pubmed18926908 Pubmed19261456 Pubmed8717519 Reactome Database ID Release 43983169 Reactome, http://www.reactome.org ReactomeREACT_75820 Reviewed: Elliott, T, 2011-02-10 Antigen processing-Cross presentation Antigen Presentation: Folding, assembly and peptide loading of class I MHC