title: A flexible brace maintains the assembly of a hexameric replicative helicase during DNA unwinding.
abstract: 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.
authors: York Structural Biology Laboratory, The University of York, York YO10 5DD, UK.
authors: Fiona
authors: F
authors: Whelan
authors: Jonathan A
authors: JA
authors: Stead
authors: Alexander V
authors: AV
authors: Shkumatov
authors: Dmitri I
authors: DI
authors: Svergun
authors: Cyril M
authors: CM
authors: Sanders
authors: Alfred A
authors: AA
authors: Antson
mesh_terms: D000595:Amino Acid Sequence; D017124:Conserved Sequence; D004265:DNA Helicases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry; D053838:Scattering, Small Angle; D017384:Sequence Deletion; D055672:Static Electricity; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D004268:DNA-Binding Proteins; C069814:E1 protein, Bovine papillomavirus; D021122:Protein Subunits; D014764:Viral Proteins; D004265:DNA Helicases