title: Components of the ubiquitin-proteasome pathway compete for surfaces on Rad23 family proteins.
abstract: BACKGROUND
  The delivery of ubiquitinated proteins to the proteasome for degradation is a key step in the regulation of the ubiquitin-proteasome pathway, yet the mechanisms underlying this step are not understood in detail. The Rad23 family of proteins is known to bind ubiquitinated proteins through its two ubiquitin-associated (UBA) domains, and may participate in the delivery of ubiquitinated proteins to the proteasome through docking via the Rad23 ubiquitin-like (UBL) domain.
  
  
  RESULTS
  In this study, we investigate how the interaction between the UBL and UBA domains may modulate ubiquitin recognition and the delivery of ubiquitinated proteins to the proteasome by autoinhibition. We have explored a competitive binding model using specific mutations in the UBL domain. Disrupting the intramolecular UBL-UBA domain interactions in HHR23A indeed potentiates ubiquitin-binding. Additionally, the analogous surface on the Rad23 UBL domain overlaps with that required for interaction with both proteasomes and the ubiquitin ligase Ufd2. We have found that mutation of residues on this surface affects the ability of Rad23 to deliver ubiquitinated proteins to the proteasome.
  
  
  CONCLUSIONS
  We conclude that the competition of ubiquitin-proteasome pathway components for surfaces on Rad23 is important for the role of the Rad23 family proteins in proteasomal targeting.
authors.affiliation: Department of Pathology, Harvard Medical School, Boston, Massachusetts, USA. amgoh@imcb.a-star.edu.sg
authors.forename: Amanda M
authors.initials: AM
authors.lastname: Goh
authors.forename: Kylie J
authors.initials: KJ
authors.lastname: Walters
authors.forename: Suzanne
authors.initials: S
authors.lastname: Elsasser
authors.forename: Rati
authors.initials: R
authors.lastname: Verma
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Deshaies
authors.forename: Daniel
authors.initials: D
authors.lastname: Finley
authors.forename: Peter M
authors.initials: PM
authors.lastname: Howley
mesh_terms: D001667:Binding, Competitive / Q000235:genetics; D045643:DNA Repair Enzymes / Q000737:chemistry* / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D008954:Models, Biological; D009154:Mutation; D025821:Polyubiquitin / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000235:genetics; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; D025801:Ubiquitin; D025821:Polyubiquitin; C086985:RAD23A protein, human; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex; D045643:DNA Repair Enzymes