PathwayStep6579 PathwayStep6580 PathwayStep6581 PathwayStep6584 PathwayStep6585 PathwayStep6582 PathwayStep6583 PathwayStep6572 PathwayStep6573 PathwayStep6574 PathwayStep6575 PathwayStep6576 PathwayStep6577 PathwayStep6578 Transport of MHC heterotrimer to ER exit site Loading of antigenic peptides on to class I MHC Trimming of peptides in ER Transport of Antigen peptide in to ER Disassembly of COPII coated vesicle Budding of COPII coated vesicle Recruitment of Sec31p:Sec13p to prebudding complex and formation of COPII vesicle Capturing cargo and formation of prebudding complex Journey of cargo through Golgi complex Expression of peptide bound class I MHC on cell surface Formation of peptide loading complex (PLC) Interaction of beta-2-microglobulin (B2M) chain with class I HC Interaction of Erp57 with MHC class I HC Binding of newly synthesized MHC class I heavy chain (HC) with calnexin Antigen Presentation: Folding, assembly and peptide loading of class I MHC Authored: Garapati, P V, 2010-10-29 Edited: Garapati, P V, 2010-10-29 Pubmed12495737 Pubmed15224092 Pubmed18641646 Pubmed18926908 Pubmed19178136 Reactome Database ID Release 43983170 Reactome, http://www.reactome.org ReactomeREACT_75795 Reviewed: Elliott, T, 2011-02-10 Unlike other glycoproteins, correct folding of MHC class I molecules is not sufficient to trigger their exit from the ER, they exit only after peptide loading. Described here is the process of antigen presentation which consists of the folding, assembly, and peptide loading of MHC class I molecules. The newly synthesized MHC class I Heavy Chain (HC) is initially folded with the help of several chaperones (calnexin, BiP, ERp57) and then binds with Beta-2-microglobulin (B2M). This MHC:B2M heterodimer enters the peptide loading complex (PLC), a multiprotein complex that includes calreticulin, endoplasmic reticulum resident protein 57 (ERp57), transporter associated with antigen processing (TAP) and tapasin. Peptides generated from Ub-proteolysis are transported into the ER through TAP. These peptides are further trimmed by ER-associated aminopeptidase (ERAP) and loaded on to MHC class I molecules. Stable MHC class I trimers with high-affinity peptide are transported from the ER to the cell surface by the Golgi apparatus.