Hexameric helicase G40P unwinds DNA in single base pair steps

Elife. 2019 Jan 28:8:e42001. doi: 10.7554/eLife.42001.


Most replicative helicases are hexameric, ring-shaped motor proteins that translocate on and unwind DNA. Despite extensive biochemical and structural investigations, how their translocation activity is utilized chemo-mechanically in DNA unwinding is poorly understood. We examined DNA unwinding by G40P, a DnaB-family helicase, using a single-molecule fluorescence assay with a single base pair resolution. The high-resolution assay revealed that G40P by itself is a very weak helicase that stalls at barriers as small as a single GC base pair and unwinds DNA with the step size of a single base pair. Binding of a single ATPγS could stall unwinding, demonstrating highly coordinated ATP hydrolysis between six identical subunits. We observed frequent slippage of the helicase, which is fully suppressed by the primase DnaG. We anticipate that these findings allow a better understanding on the fine balance of thermal fluctuation activation and energy derived from hydrolysis.

Keywords: DnaB; DnaG; G40P; molecular biophysics; none; single-molecule FRET; structural biology.

Publication types

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

MeSH terms

  • Adenosine Triphosphate / analogs & derivatives
  • Adenosine Triphosphate / metabolism
  • Base Composition
  • Base Pairing*
  • DNA / metabolism
  • DNA Helicases / metabolism*
  • DNA Primase / metabolism
  • Hydrolysis
  • Protein Multimerization*
  • Protein Subunits / metabolism
  • Viral Proteins / metabolism*


  • Protein Subunits
  • Viral Proteins
  • adenosine 5'-O-(3-thiotriphosphate)
  • Adenosine Triphosphate
  • DNA
  • DNA Primase
  • DNA Helicases
  • G40P helicase protein, Bacteriophage SPP1