Author/Authors :
Bogdan I. Florea، نويسنده , , Martijn Verdoes، نويسنده , , Nan Li، نويسنده , , Wouter A. van der Linden، نويسنده , , Paul P. Geurink، نويسنده , , Hans van den Elst، نويسنده , , Tanja Hofmann، نويسنده , , Arnoud de Ru، نويسنده , , Peter A. van Veelen، نويسنده , , Keiji Tanaka، نويسنده , , Katsuhiro Sasaki، نويسنده , , Shigeo Murata، نويسنده , , Hans den Dulk، نويسنده , , Jaap Brouwer، نويسنده , , Ferry A. Ossendorp، نويسنده , , Alex، نويسنده ,
Abstract :
Epithelial cells of the thymus cortex express a unique proteasome particle involved in positive T cell selection. This thymoproteasome contains the recently discovered β5t subunit that has an uncharted activity, if any. We synthesized fluorescent epoxomicin probes that were used in a chemical proteomics approach, entailing activity-based profiling, affinity purification, and LC-MS identification, to demonstrate that the β5t subunit is catalytically active in the murine thymus. A panel of established proteasome inhibitors showed that the broad-spectrum inhibitor epoxomicin blocks the β5t activity and that the subunit-specific antagonists bortezomib and NC005 do not inhibit β5t. We show that β5t has a substrate preference distinct from β5/β5i that might explain how the thymoproteasome generates the MHC class I peptide repertoire needed for positive T cell selection.
