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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
PubMed

Insights

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.

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.

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