title: Substrate Ubiquitination Controls the Unfolding Ability of the Proteasome.
abstract: In eukaryotic cells, proteins are targeted to the proteasome for degradation by polyubiquitination. These proteins bind to ubiquitin receptors, are engaged and unfolded by proteasomal ATPases, and are processively degraded. The factors determining to what extent the proteasome can successfully unfold and degrade a substrate are still poorly understood. We find that the architecture of polyubiquitin chains attached to a substrate affects the ability of the proteasome to unfold and degrade the substrate, with K48- or mixed-linkage chains leading to greater processivity than K63-linked chains. Ubiquitin-independent targeting of substrates to the proteasome gave substantially lower processivity of degradation than ubiquitin-dependent targeting. Thus, even though ubiquitin chains are removed early in degradation, during substrate engagement, remarkably they dramatically affect the later unfolding of a protein domain. Our work supports a model in which a polyubiquitin chain associated with a substrate switches the proteasome into an activated state that persists throughout the degradation process.
authors.affiliation: From the Department of Chemistry, Villanova University, Villanova, Pennsylvania 19085.
authors.forename: Eden L
authors.initials: EL
authors.lastname: Reichard
authors.affiliation: From the Department of Chemistry, Villanova University, Villanova, Pennsylvania 19085.
authors.forename: Giavanna G
authors.initials: GG
authors.lastname: Chirico
authors.affiliation: From the Department of Chemistry, Villanova University, Villanova, Pennsylvania 19085.
authors.forename: William J
authors.initials: WJ
authors.lastname: Dewey
authors.affiliation: From the Department of Chemistry, Villanova University, Villanova, Pennsylvania 19085.
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Nassif
authors.affiliation: From the Department of Chemistry, Villanova University, Villanova, Pennsylvania 19085.
authors.forename: Katelyn E
authors.initials: KE
authors.lastname: Bard
authors.affiliation: From the Department of Chemistry, Villanova University, Villanova, Pennsylvania 19085.
authors.forename: Nickolas E
authors.initials: NE
authors.lastname: Millas
authors.affiliation: From the Department of Chemistry, Villanova University, Villanova, Pennsylvania 19085 daniel.kraut@villanova.edu.
authors.forename: Daniel A
authors.identifier: 0000-0002-4428-5832
authors.initials: DA
authors.lastname: Kraut
mesh_terms: D006801:Humans; D008954:Models, Biological; D025821:Polyubiquitin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D058767:Protein Unfolding; D059748:Proteolysis; D054875:Ubiquitination
chemical_list: D025821:Polyubiquitin; D046988:Proteasome Endopeptidase Complex
keywords: ATP-dependent protease; ATPases associated with diverse cellular activities (AAA); enzyme kinetics; enzyme mechanism; pre-steady-state kinetics; proteasome; protein degradation; protein unfolding