title: Repeat sequence of Epstein-Barr virus-encoded nuclear antigen 1 protein interrupts proteasome substrate processing.
abstract: The Epstein-Barr virus thwarts immune surveillance through a Gly-Ala repeat (GAr) within the viral Epstein-Barr virus-encoded nuclear antigen 1 protein. The GAr inhibits proteasome processing, an early step in antigen peptide presentation, but the mechanism of proteasome inhibition has been unclear. By embedding a GAr within ornithine decarboxylase, a natural proteasome substrate that does not require ubiquitin conjugation, we now demonstrate inhibition in a purified system, excluding involvement of ubiquitin conjugation or of proteins extraneous to substrate and proteasome. We show further that the GAr acts as a stop-transfer signal in proteasome substrate processing, resulting in vivo in partial proteolysis that halts just short of the GAr. Similarly, introducing a GAr into green fluorescent protein destabilized by the ornithine decarboxylase degradation domain also stops the progress of proteolysis, leading to the accumulation of partial degradation products. We postulate that the ATP motor of the proteasome slips when it encounters the GAr, impeding further insertion and, in this way, halting degradation.
authors.affiliation: Department of Microbiology and Immunology, University of California, San Francisco, California 94143, USA.
authors.forename: Mingsheng
authors.initials: M
authors.lastname: Zhang
authors.forename: Philip
authors.initials: P
authors.lastname: Coffino
mesh_terms: D000818:Animals; D017951:Antigen Presentation; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D019309:Epstein-Barr Virus Nuclear Antigens / Q000235:genetics / Q000378:metabolism*; D004854:Herpesvirus 4, Human / Q000276:immunology / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism*; D009955:Ornithine Decarboxylase / Q000276:immunology / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D051381:Rats; D020449:Repetitive Sequences, Amino Acid; D012441:Saccharomyces cerevisiae
chemical_list: D019309:Epstein-Barr Virus Nuclear Antigens; D009097:Multienzyme Complexes; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D009955:Ornithine Decarboxylase