Peptide Binding and Intracellular Transport of MHC Molecules

Abstract

The function of MHC molecules is to present fragments of antigen in the form of peptides to T cell receptors. In general, MHC Class I molecules will present fragments derived from mitochondrial, cytoplasmic or ER molecules. MHC Class II will present fragments from antigens that are degraded in endosomes and lysosomes. This includes cell surface proteins and soluble proteins present in the medium. These introductory statements illustrate the central cell biological questions related to MHC Class l and II molecules: how and where are the antigenic peptides generated and how and where do MHC molecules associate with them? These questions are of some relevance because the type of peptides that bind to MHC molecules will determine the outcome of any T cell response. Although the binding of peptides by MHC Class I molecules has a number of aspects in common to peptide binding by MHC Class II molecules, they differ in other aspects of peptide binding and, in particular, intracellular transport.