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Hexameric ring structure of the full-length archaeal MCM protein complex
Tillmann Pape1, Hedije Meka, Shaoxia Chen
1Department of Biological Sciences, Imperial College, London SW7 2AZ, UK.
EMBO Reports
|October 21, 2003
Summary
The minichromosome maintenance (MCM) complex, crucial for DNA replication, forms a ring structure in Archaea. This structure differs from typical helicases, suggesting a unique DNA replication mechanism.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Eukaryotic DNA replication relies on six homologous minichromosome maintenance (MCM) proteins.
- Some Archaea utilize a single MCM protein forming a homomeric assembly, likely functioning as a helicase.
- Understanding archaeal MCM structure provides insights into conserved DNA replication mechanisms.
Purpose of the Study:
- To determine the three-dimensional structure of the full-length MCM complex from Methanobacterium thermoautotrophicum.
- To elucidate the arrangement of MCM monomers and their potential role in DNA binding and helicase activity.
Main Methods:
- Three-dimensional reconstruction using electron microscopy.
- Integration of crystal structure data of MCM fragments and AAA+ hexamer models.
- Analysis of electron density maps to infer domain organization.
Main Results:
- A ring-shaped MCM complex composed of six monomers arranged around a sixfold axis was resolved.
- The complex features a large central cavity and lateral holes, capable of accommodating double-stranded DNA.
- The carboxy-terminal domain appears situated at the interface between the amino-terminal and AAA+ domains.
Conclusions:
- The archaeal MCM structure suggests a mechanism distinct from traditional hexameric helicases.
- The MCM complex may share functional similarities with SV40 large T antigen or double-stranded DNA translocases.
- This structural insight advances our understanding of DNA replication machinery evolution and function.