Production of spliced peptides by the proteasome Nathalie Vigneron1,2, Vincent Stroobant1,2, Violette Ferrari1,2, Joanna Abi Habib1,2, Benoit J. Van den Eynde1,2,3* 1Ludwig Institute for Cancer Research, Brussels, Belgium 2de Duve Institute, Université catholique de Louvain, Brussels, Belgium 3WELBIO (Walloon Excellence in Life Sciences and Biotechnology), Brussels, Belgium Running title: Peptide splicing by the proteasome *Author to whom correspondence should be addressed: Dr. Van den Eynde, Ludwig Institute for Cancer Research, de Duve Institute, Université catholique de Louvain, Avenue Hippocrate 75 B1.74.03, B-1200 Brussels, Belgium; Tel.: +32-2-7647580; Fax: +32-2-7647590; E-Mail:
[email protected]. Keywords: proteasome, CD8+ cytolytic T lymphocytes, peptide splicing, transpeptidation, antigenic peptides Abstract CD8+ cytolytic T lymphocytes are essential players of anti-tumor immune responses. On tumors, they recognize peptides of about 8-to-10 amino acids that generally result from the degradation of cellular proteins by the proteasome. Until a decade ago, these peptides were thought to solely correspond to linear fragments of proteins that were liberated after the hydrolysis of the peptide bonds located at their extremities. However, several examples of peptides containing two fragments originally distant in the protein sequence challenged this concept and demonstrated that proteasome could also splice peptides together by creating a new peptide bond between two distant fragments. Unexpectedly, peptide splicing emerges as an essential way to increase the peptide repertoire diversity as these spliced peptides were shown to represent up to 25% of the peptides presented on a cell by MHC class I. Here, we review the different steps that led to the discovery of peptide splicing by the proteasome as well as the lightening offered by the recent progresses of mass spectrometry and bioinformatics in the analysis of the spliced peptide repertoire.