Flexibility of the rings: Structural asymmetry in the DnaB hexameric helicase

Shixin Yang, Xiong Yu, Margaret S. VanLoock, Maria J. Jezewska, Wlodzimierz Bujalowski, Edward H. Egelman

    Research output: Contribution to journalArticlepeer-review

    68 Scopus citations

    Abstract

    DnaB is the primary replicative helicase in Escherichia coli and the hexameric DnaB ring has previously been shown to exist in two states in the presence of nucleotides. In one, all subunits are equivalent, while in the other, there are two different subunit conformations resulting in a trimer of dimers. Under all conditions that we have used for electron microscopy, including the absence of nucleotide, some rings exist as trimers of dimers, showing that the symmetry of the DnaB hexamer can be broken prior to nucleotide binding. Three-dimensional reconstructions reveal that the N-terminal domain of DnaB makes two very different contacts with neighboring subunits in the trimer of dimers, but does not form a predicted dimer with a neighboring N-terminal domain. Within the trimer of dimers, the helicase domain exists in two alternate conformations, each of which can form symmetrical hexamers depending upon the nucleotide cofactor used. These results provide new information about the modular architecture and domain dynamics of helicases, and suggest, by comparison with the hexameric bacteriophage T7 gp4 and SV40 large T-antigen helicases, that a great structural and mechanistic diversity may exist among the hexameric helicases.

    Original languageEnglish (US)
    Pages (from-to)839-849
    Number of pages11
    JournalJournal of Molecular Biology
    Volume321
    Issue number5
    DOIs
    StatePublished - Jan 1 2002

    Keywords

    • Electron microscopy
    • Helicases
    • Image analysis

    ASJC Scopus subject areas

    • Structural Biology
    • Molecular Biology

    Fingerprint Dive into the research topics of 'Flexibility of the rings: Structural asymmetry in the DnaB hexameric helicase'. Together they form a unique fingerprint.

    Cite this