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Updated: Apr 23, 2026
X-Ray Crystallography to Study the Oligomeric State Transition of the Thermotoga maritima M42 Aminopeptidase TmPep1050
Published on: May 13, 2020
Analysis of the crystal structure of an active MCM hexamer
Justin M Miller1, Buenafe T Arachea1, Leslie B Epling1
1Department of Structural Biology, St Jude Children's Research Hospital, Memphis, United States.
Abstract:
In a previous Research article (Froelich et al., 2014), we suggested an MCM helicase activation mechanism, but were limited in discussing the ATPase domain because it was absent from the crystal structure. Here we present the crystal structure of a nearly full-length MCM hexamer that is helicase-active and thus has all features essential for unwinding DNA. The structure is a chimera of Sulfolobus solfataricus N-terminal domain and Pyrococcus furiosus ATPase domain. We discuss three major findings: 1) a novel conformation for the A-subdomain that could play a role in MCM regulation; 2) interaction of a universally conserved glutamine in the N-terminal Allosteric Communication Loop with the AAA+ domain helix-2-insert (h2i); and 3) a recessed binding pocket for the MCM ssDNA-binding motif influenced by the h2i. We suggest that during helicase activation, the h2i clamps down on the leading strand to facilitate strand retention and regulate ATP hydrolysis.
Insights
This study reveals the crystal structure of a nearly full-length, active MCM helicase. The structure elucidates key interactions and conformations crucial for DNA unwinding and MCM helicase regulation.
Area of Science:
- Molecular Biology
- Structural Biology
- Biochemistry
Background:
- Previous research proposed an MCM helicase activation mechanism but lacked structural data for the ATPase domain.
- The MCM helicase is essential for DNA replication and requires ATP hydrolysis for its function.
Purpose of the Study:
- To present the crystal structure of a nearly full-length, helicase-active MCM hexamer.
- To elucidate the structural basis of MCM helicase activation and regulation.
Main Methods:
- X-ray crystallography was used to determine the structure of a chimeric MCM hexamer.
- The chimera combined N-terminal domains from *Sulfolobus solfataricus* and ATPase domains from *Pyrococcus furiosus*.
Main Results:
- A novel conformation of the A-subdomain, potentially involved in MCM regulation, was identified.
- A conserved glutamine in the N-terminal Allosteric Communication Loop interacts with the AAA+ domain helix-2-insert (h2i).
- The h2i influences a recessed binding pocket for the MCM single-stranded DNA (ssDNA)-binding motif.
Conclusions:
- The h2i likely clamps onto the leading DNA strand during helicase activation, aiding strand retention and regulating ATP hydrolysis.
- This structural insight provides a mechanistic understanding of MCM helicase function and regulation.
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