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The DnaB.DnaC complex: a structure based on dimers assembled around an occluded channel
M Bárcena1, T Ruiz, L E Donate
1Centro Nacional de Biotecnología (CSIC), Campus Universidad Autónoma de Madrid, 28049 Madrid, Spain.
The EMBO Journal
|March 17, 2001
Summary
The structure of the Escherichia coli DnaB helicase complexed with DnaC reveals how DnaC controls helicase activity. This structural insight explains DnaC
Area of Science:
- Molecular Biology
- Structural Biology
- Biochemistry
Background:
- Replicative helicases are essential motor proteins that unwind DNA during replication.
- Escherichia coli DnaB is a well-studied replicative helicase crucial for DNA replication.
- Understanding the interaction between DnaB and its loading partner DnaC is key to comprehending helicase regulation.
Purpose of the Study:
- To determine the three-dimensional structure of the DnaB-DnaC complex.
- To elucidate the structural basis for DnaC-mediated regulation of DnaB helicase activity.
- To provide insights into the mechanism of helicase loading and inactivation.
Main Methods:
- Cryo-electron microscopy was used to obtain the 2.6 Å resolution structure.
- Computational analysis of the electron microscopy density map.
- Structural interpretation of protein-protein interactions within the complex.
Main Results:
- The DnaB hexamer forms a complex with DnaC, revealing intricate protein-protein interactions.
- DnaC monomers assemble into three dimers that interlock with the DnaB hexamer.
- This interaction likely stabilizes DnaB in a C(3) symmetric state, inactivating the helicase.
- The central channel of DnaB is occluded, preventing DNA passage.
Conclusions:
- The structure provides a molecular mechanism for DnaC's role in regulating DnaB helicase.
- DnaC binding induces a conformational change in DnaB, inhibiting its unwinding activity.
- The DnaB N-terminal domain is proposed to be located at the DnaC-binding face.