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Hybrid Ensemble and Single-molecule Assay to Image the Motion of Fully Reconstituted CMG

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Molecular architecture of a multifunctional MCM complex.

June Sanchez-Berrondo¹, Pablo Mesa, Arkaitz Ibarra

¹Structural Biology and Biocomputing Programme, Macromolecular Crystallography Group, Spanish National Cancer Research Center (CNIO), c/Melchor Fdez. Almagro 3, 28029-Madrid, Spain.

Nucleic Acids Research

|October 11, 2011

Summary

Researchers isolated a novel Bacillus cereus helicase-primase complex (BcMCM) with DNA binding, helicase, primase, and polymerase activities. Structural analysis revealed a hexameric ring shape, suggesting a DNA unwinding mechanism similar to papillomavirus E1 helicase.

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Area of Science:

Molecular Biology
Structural Biology
Biochemistry

Background:

DNA replication relies on regulated protein complexes, including replicative helicases.
Bacillus cereus harbors a prophage-encoded MCM helicase fused with a primase domain.

Purpose of the Study:

To isolate and characterize the Bacillus cereus helicase-primase complex (BcMCM).
To elucidate the structural and mechanistic properties of BcMCM, including its DNA binding and enzymatic activities.

Main Methods:

Isolation and purification of the BcMCM complex.
Biochemical assays to determine helicase, primase, and DNA polymerase activities.
Single-particle electron microscopy and 3D reconstruction to determine complex structure.
Site-directed mutagenesis to investigate the DNA unwinding mechanism.

Main Results:

The isolated BcMCM complex exhibits DNA binding, helicase, primase, and DNA polymerase activities.
Structural analysis revealed a hexameric ring structure typical of MCM helicases.
Mutagenesis studies suggest BcMCM unwinds DNA via an extrusion model, akin to papillomavirus E1 helicase.

Conclusions:

The BcMCM complex represents an integrated helicase-primase system with multiple enzymatic functions.
Its hexameric structure and proposed unwinding mechanism provide insights into DNA replication machinery.