The structure and function of MCM from archaeal M. Thermoautotrophicum


Eukaryotic chromosomal DNA is licensed for replication precisely once in each cell cycle. The mini-chromosome maintenance (MCM) complex plays a role in this replication licensing. We have determined the structure of a fragment of MCM from Methanobacterium thermoautotrophicum (mtMCM), a model system for eukaryotic MCM. The structure reveals a novel dodecameric architecture with a remarkably long central channel. The channel surface has an unusually high positive charge and binds DNA. We also show that the structure of the N-terminal fragment is conserved for all MCMs proteins despite highly divergent sequences, suggesting a common architecture for a similar task: gripping/remodeling DNA and regulating MCM activity. An mtMCM mutant protein equivalent to a yeast MCM5 (CDC46) protein with the bob1 mutation at its N terminus has only subtle structural changes, suggesting a Cdc7-bypass mechanism by Bob1 in yeast. Yeast bypass experiments using MCM5 mutant proteins support the hypothesis for the bypass mechanism.

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Figure 1: Overall structure of double-hexamer of N-mtMCM.
Figure 2: The fold and assembly of N-mtMCM.
Figure 3: Unique features of the channel of N-mtMCM and comparison of the channels between N-mtMCM, T7gp4 and PCNA.
Figure 4: Central channel of N-mtMCM double-hexamer and DNA binding.
Figure 5: The structural conservation of the N-terminal half of all MCMs and the structure of N-mtMCM mutant protein with a mutation at the conserved position corresponding to the yeast mcm5-bob1 mutation.
Figure 6: Yeast bypass results of mutations of MCM5 at Pro83 supporting the domain-push hypothesis for bob1 bypass mechanism.

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  • 10 February 2003

    Corrected HTML, added footnote


  1. 1.

    *Note: In the version of this article initially published online, this paper contained two mistakes. The first mistake is in the legend of Fig. 3b; the correct legend should read: "b, Side view of the N-mtMCM dodecamer showing the predominantly negatively charged (red) outer surface". The second mistake is in the first paragraph of page 5 (third line from the top); the correct sentence should read: "A surface charge calculation shows that the inner surface of the entire channel is strongly positive (Fig. 3c); in contrast, the outside surface is mostly negative (Fig. 3b)". This mistake has been corrected in the HTML and print versions of the article.


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We thank S. Harrison for comments on the manuscript, L. Pessoa-Brandão, R. Zhao, D. Li, T. Gould and L. Wilson for assistance and other members of the Chen group for comments and input; R. Zhang at 19id in Argonne National Laboratory (APS) and the staff at 14bmc in APS and X25 and X4A in Brookhaven National Laboratory for assistance in data collection; and the UCHSC X-ray center in Biomolecular Structure Program for support. This work is supported by start-up and cancer-center funds from UCHSC to X.C. and an NIH grant to R.S.

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Correspondence to Xiaojiang S. Chen.

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