title: Parkin mediates apparent E2-independent monoubiquitination in vitro and contains an intrinsic activity that catalyzes polyubiquitination.
abstract: BACKGROUND
  Mutations in the parkin gene, which encodes a ubiquitin ligase (E3), are a major cause of autosomal recessive parkinsonism. Although parkin-mediated ubiquitination was initially linked to protein degradation, accumulating evidence suggests that the enzyme is capable of catalyzing multiple forms of ubiquitin modifications including monoubiquitination, K48- and K63-linked polyubiquitination. In this study, we sought to understand how a single enzyme could exhibit such multifunctional catalytic properties.
  
  
  RESULTS
  By means of in vitro ubiquitination assays coupled with mass spectrometry analysis, we were surprised to find that parkin is apparently capable of mediating E2-independent protein ubiquitination in vitro, an unprecedented activity exhibited by an E3 member. Interestingly, whereas full length parkin catalyzes solely monoubiquitination regardless of the presence or absence of E2, a truncated parkin mutant containing only the catalytic moiety supports both E2-independent and E2-dependent assembly of ubiquitin chains.
  
  
  CONCLUSIONS
  Our results here suggest a complex regulation of parkin's activity and may help to explain how a single enzyme like parkin could mediate diverse forms of ubiquitination.
authors.affiliation: Department of Physiology, National University of Singapore, Singapore, Singapore.
authors.forename: Katherine C M
authors.initials: KC
authors.lastname: Chew
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Matsuda
authors.forename: Keiko
authors.initials: K
authors.lastname: Saisho
authors.forename: Grace G Y
authors.initials: GG
authors.lastname: Lim
authors.forename: Chou
authors.initials: C
authors.lastname: Chai
authors.forename: Hui-Mei
authors.initials: HM
authors.lastname: Tan
authors.forename: Keiji
authors.initials: K
authors.lastname: Tanaka
authors.forename: Kah-Leong
authors.initials: KL
authors.lastname: Lim
mesh_terms: D002384:Catalysis; D006801:Humans; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases; C111567:parkin protein