A flexible brace maintains the assembly of a hexameric replicative helicase during DNA unwinding

Fiona Whelan, Jonathan A Stead, Alexander V Shkumatov, Dmitri I Svergun, Cyril M Sanders, Alfred A Antson

Research output: Contribution to journalArticlepeer-review


The mechanism of DNA translocation by papillomavirus E1 and polyomavirus LTag hexameric helicases involves consecutive remodelling of subunit-subunit interactions around the hexameric ring. Our biochemical analysis of E1 helicase demonstrates that a 26-residue C-terminal segment is critical for maintaining the hexameric assembly. As this segment was not resolved in previous crystallographic analysis of E1 and LTag hexameric helicases, we determined the solution structure of the intact hexameric E1 helicase by Small Angle X-ray Scattering. We find that the C-terminal segment is flexible and occupies a cleft between adjacent subunits in the ring. Electrostatic potential calculations indicate that the negatively charged C-terminus can bridge the positive electrostatic potentials of adjacent subunits. Our observations support a model in which the C-terminal peptide serves as a flexible 'brace' maintaining the oligomeric state during conformational changes associated with ATP hydrolysis. We argue that these interactions impart processivity to DNA unwinding. Sequence and disorder analysis suggest that this mechanism of hexamer stabilization would be conserved among papillomavirus E1 and polyomavirus LTag hexameric helicases.

Original languageEnglish
Pages (from-to)2271-2283
Number of pages13
JournalNucleic Acids Research
Issue number5
Early online date8 Nov 2011
Publication statusPublished - Mar 2012


  • Amino Acid Sequence
  • Conserved Sequence
  • DNA Helicases
  • DNA-Binding Proteins
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Multimerization
  • Protein Structure, Tertiary
  • Protein Subunits
  • Scattering, Small Angle
  • Sequence Deletion
  • Static Electricity
  • Viral Proteins
  • X-Ray Diffraction

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