title: A proteasomal ATPase subunit recognizes the polyubiquitin degradation signal.
abstract: The 26S proteasome is the chief site of regulatory protein turnover in eukaryotic cells. It comprises one 20S catalytic complex (composed of four stacked rings of seven members) and two axially positioned 19S regulatory complexes (each containing about 18 subunits) that control substrate access to the catalytic chamber. In most cases, targeting to the 26S proteasome depends on tagging of the substrate with a specific type of polyubiquitin chain. Recognition of this signal is followed by substrate unfolding and translocation, which are presumably catalysed by one or more of six distinct AAA ATPases located in the base-a ring-like 19S subdomain that abuts the axial pore of the 20S complex and exhibits chaperone activity in vitro. Despite the importance of polyubiquitin chain recognition in proteasome function, the site of this signal's interaction with the 19S complex has not been identified previously. Here we use crosslinking to a reactive polyubiquitin chain to show that a specific ATPase subunit, S6' (also known as Rpt5), contacts the bound chain. The interaction of this signal with 26S proteasomes is modulated by ATP hydrolysis. Our results suggest that productive recognition of the proteolytic signal, as well as proteasome assembly and substrate unfolding, are ATP-dependent events.
authors.affiliation: Department of Biochemistry and Molecular Biology, School of Public Health, Johns Hopkins University, Baltimore, Maryland, USA.
authors.forename: Y Amy
authors.initials: YA
authors.lastname: Lam
authors.forename: T Glen
authors.initials: TG
authors.lastname: Lawson
authors.forename: Murugesan
authors.initials: M
authors.lastname: Velayutham
authors.forename: Jay L
authors.initials: JL
authors.lastname: Zweier
authors.forename: Cecile M
authors.initials: CM
authors.lastname: Pickart
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002417:Cattle; D003432:Cross-Linking Reagents; D004578:Electron Spin Resonance Spectroscopy; D006868:Hydrolysis; D010447:Peptide Hydrolases / Q000737:chemistry* / Q000378:metabolism*; D025821:Polyubiquitin / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D021122:Protein Subunits; D013379:Substrate Specificity
chemical_list: D003432:Cross-Linking Reagents; D021122:Protein Subunits; D025821:Polyubiquitin; D000255:Adenosine Triphosphate; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D000251:Adenosine Triphosphatases