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Physical basis for the loading of a bacterial replicative helicase onto DNA

DOI: 10.1016/j.molcel.2019.01.023 DOI Help

Authors: Ernesto Arias-palomo (Centro de Investigaciones Biológicas, CIB-CSIC) , Neha Puri (Johns Hopkins University School of Medicine) , Valerie L. O’shea Murray (Johns Hopkins University School of Medicine) , Qianyun Yan (Johns Hopkins University School of Medicine) , James M. Berger (Johns Hopkins University School of Medicine)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Molecular Cell , VOL 74 , PAGES 173 - 184.e4

State: Published (Approved)
Published: April 2019
Diamond Proposal Number(s): 19454

Abstract: In cells, dedicated AAA+ ATPases deposit hexameric, ring-shaped helicases onto DNA to initiate chromosomal replication. To better understand the mechanisms by which helicase loading can occur, we used cryo-EM to determine sub-4-Å-resolution structures of the E. coli DnaB⋅DnaC helicase⋅loader complex with nucleotide in pre- and post-DNA engagement states. In the absence of DNA, six DnaC protomers latch onto and crack open a DnaB hexamer using an extended N-terminal domain, stabilizing this conformation through nucleotide-dependent ATPase interactions. Upon binding DNA, DnaC hydrolyzes ATP, allowing DnaB to isomerize into a topologically closed, pre-translocation state competent to bind primase. Our data show how DnaC opens the DnaB ring and represses the helicase prior to DNA binding and how DnaC ATPase activity is reciprocally regulated by DnaB and DNA. Comparative analyses reveal how the helicase loading mechanism of DnaC parallels and diverges from homologous AAA+ systems involved in DNA replication and transposition.

Journal Keywords: DNA replication; helicase; helicase loader; DnaB; DnaC; AAA+ ATPases; cryo-EM

Subject Areas: Biology and Bio-materials

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