Biochemical characterization of Warsaw breakage syndrome helicase

J Biol Chem. 2012 Jan 6;287(2):1007-21. doi: 10.1074/jbc.M111.276022. Epub 2011 Nov 18.

Abstract

Mutations in the human ChlR1 gene are associated with a unique genetic disorder known as Warsaw breakage syndrome characterized by cellular defects in sister chromatid cohesion and hypersensitivity to agents that induce replication stress. A role of ChlR1 helicase in sister chromatid cohesion was first evidenced by studies of the yeast homolog Chl1p; however, its cellular functions in DNA metabolism are not well understood. We carefully examined the DNA substrate specificity of purified recombinant human ChlR1 protein and the biochemical effect of a patient-derived mutation, a deletion of a single lysine (K897del) in the extreme C terminus of ChlR1. The K897del clinical mutation abrogated ChlR1 helicase activity on forked duplex or D-loop DNA substrates by perturbing its DNA binding and DNA-dependent ATPase activity. Wild-type ChlR1 required a minimal 5' single-stranded DNA tail of 15 nucleotides to efficiently unwind a simple duplex DNA substrate. The additional presence of a 3' single-stranded DNA tail as short as five nucleotides dramatically increased ChlR1 helicase activity, demonstrating the preference of the enzyme for forked duplex structures. ChlR1 unwound G-quadruplex (G4) DNA with a strong preference for a two-stranded antiparallel G4 (G2') substrate and was only marginally active on a four-stranded parallel G4 structure. The marked difference in ChlR1 helicase activity on the G4 substrates, reflected by increased binding to the G2' substrate, distinguishes ChlR1 from the sequence-related FANCJ helicase mutated in Fanconi anemia. The biochemical results are discussed in light of the known cellular defects associated with ChlR1 deficiency.

Publication types

  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Basic-Leucine Zipper Transcription Factors / chemistry
  • Basic-Leucine Zipper Transcription Factors / genetics
  • Basic-Leucine Zipper Transcription Factors / metabolism
  • DEAD-box RNA Helicases / chemistry*
  • DEAD-box RNA Helicases / genetics
  • DEAD-box RNA Helicases / metabolism
  • DNA / chemistry*
  • DNA / genetics
  • DNA / metabolism
  • DNA Helicases / chemistry*
  • DNA Helicases / genetics
  • DNA Helicases / metabolism
  • DNA Repair-Deficiency Disorders / enzymology*
  • DNA Repair-Deficiency Disorders / genetics
  • Fanconi Anemia Complementation Group Proteins / chemistry
  • Fanconi Anemia Complementation Group Proteins / genetics
  • Fanconi Anemia Complementation Group Proteins / metabolism
  • Humans
  • Sequence Deletion
  • Substrate Specificity
  • Syndrome

Substances

  • BACH1 protein, human
  • Basic-Leucine Zipper Transcription Factors
  • Fanconi Anemia Complementation Group Proteins
  • DNA
  • DNA Helicases
  • DDX11 protein, human
  • DEAD-box RNA Helicases