RESUMO
Epitopes presented by major histocompatibility complex (MHC) class I molecules for cytotoxic T-lymphocyte (CTL) recognition are derived mainly from cytosolic proteins. Antigen presentation on the cell surface requires correct processing of epitopes by the proteasome, cytosolic and endoplasmic reticulum (ER) aminopeptidases, efficient TAP transport, and sufficient binding to MHC class I molecules. The efficiency of the epitope generation depends not only on the epitope itself but also on its flanking regions. To investigate preferences at the C-terminal epitope extension on processing and presentation, the SIINFEKL (S8L) epitope can be used as a model epitope. By exchanging the amino acids at the C-terminus of S8L, their influence on the presentation of S8L can be analyzed.
Assuntos
Apresentação de Antígeno , Epitopos de Linfócito T/genética , Epitopos de Linfócito T/imunologia , Ácidos/química , Animais , Linhagem Celular , Citometria de Fluxo , Expressão Gênica , Antígenos de Histocompatibilidade Classe I/imunologia , Humanos , Complexo de Endopeptidases do Proteassoma/imunologia , Coloração e Rotulagem , Linfócitos T Citotóxicos/imunologia , TransfecçãoRESUMO
Most peptide ligands presented by MHC class I molecules are the product of an intracellular pathway comprising protein breakdown in the cytosol, transport into the endoplasmic reticulum, and successive N-terminal trimming events. The efficiency of each of these processes depends on the amino acid sequence of the presented ligand and its precursors. Thus, relating the amino acid composition N-terminal of presented ligands to the sequence specificity of processes in the pathway gives insight into the usage of ligand precursors in vivo. Examining the amino acid composition upstream the true N terminus of MHC class I ligands, we demonstrate the existence of a distinct N-terminal processing motif comprising approximately seven residues and matching the known preferences of proteasome and TAP, two key players in ligand processing. Furthermore, we find that some residues, which are preferred by both TAP and the proteasome, are underrepresented at positions immediately preceding the N terminus of MHC class I ligands. Based on experimentally determined aminopeptidase activities, this pattern suggests trimming next to the final N terminus to take place predominantly in the endoplasmic reticulum.
