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The bacterial DnaC helicase loader is a DnaB ring breaker
Ernesto Arias-Palomo1, Valerie L O'Shea, Iris V Hood
1Department of Molecular and Cell Biology, California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA.
Cell
|April 9, 2013
Summary
Bacterial DNA replication relies on helicase loading. Researchers discovered how the DnaC loader protein remodels the DnaB helicase ring, revealing a conserved mechanism for DNA unwinding complex assembly.
Area of Science:
- Molecular Biology
- Structural Biology
- Biochemistry
Background:
- AAA+ ATPases are crucial for DNA replication, forming hexameric ring-shaped helicases.
- The loading of these helicases onto DNA by loader proteins is essential for cellular organisms.
Purpose of the Study:
- To elucidate the structural mechanism of the E. coli DnaB helicase loading by the DnaC protein.
- To understand how the DnaB⋅DnaC complex remodels the helicase ring for DNA binding.
Main Methods:
- Determining the ATP-bound structure of the DnaB⋅DnaC complex using electron microscopy and small-angle X-ray scattering (SAXS).
- Investigating the role of the DnaC AAA+ fold and its isolated domains in helicase loading and activity.
Main Results:
- The intact DnaB⋅DnaC complex (480 kDa dodecamer) forms a three-tiered assembly with DnaC in a spiral configuration.
- DnaC remodels DnaB, creating a break in the helicase ring, a process independent of DnaC's full AAA+ fold.
- An isolated DnaC binding domain effectively loads DnaB onto DNA and enhances helicase activity in vitro.
Conclusions:
- Bacterial helicase loading by DnaC shares mechanistic similarities with eukaryotic polymerase clamp loaders.
- Bacterial replicative helicases possess autoregulatory elements controlling loading and DNA unwinding by hexameric motor domains.
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