Format

Send to

Choose Destination
Mol Cell. 2019 Apr 4;74(1):173-184.e4. doi: 10.1016/j.molcel.2019.01.023. Epub 2019 Feb 20.

Physical Basis for the Loading of a Bacterial Replicative Helicase onto DNA.

Author information

1
Department of Structural & Chemical Biology, Centro de Investigaciones Biológicas, CIB-CSIC 28040 Madrid, Spain. Electronic address: earias@cib.csic.es.
2
Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
3
Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA. Electronic address: jmberger@jhmi.edu.

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.

PMID:
30797687
PMCID:
PMC6450724
[Available on 2020-04-04]
DOI:
10.1016/j.molcel.2019.01.023

Supplemental Content

Full text links

Icon for Elsevier Science
Loading ...
Support Center