Cryo-EM structure of Mcm2-7 double hexamer on DNA suggests a lagging-strand DNA extrusion model

Noguchi, Y., Yuan, Z., Bai, L., Schneider, S., Zhao, G., Stillman, B., Speck, C., Li, H. (November 2017) Cryo-EM structure of Mcm2-7 double hexamer on DNA suggests a lagging-strand DNA extrusion model. Proc Natl Acad Sci U S A, 114 (45). E9529-9538. ISSN 0027-8424

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URL: https://www.ncbi.nlm.nih.gov/pubmed/29078375
DOI: 10.1073/pnas.1712537114

Abstract

During replication initiation, the core component of the helicase-the Mcm2-7 hexamer-is loaded on origin DNA as a double hexamer (DH). The two ring-shaped hexamers are staggered, leading to a kinked axial channel. How the origin DNA interacts with the axial channel is not understood, but the interaction could provide key insights into Mcm2-7 function and regulation. Here, we report the cryo-EM structure of the Mcm2-7 DH on dsDNA and show that the DNA is zigzagged inside the central channel. Several of the Mcm subunit DNA-binding loops, such as the oligosaccharide-oligonucleotide loops, helix 2 insertion loops, and presensor 1 (PS1) loops, are well defined, and many of them interact extensively with the DNA. The PS1 loops of Mcm 3, 4, 6, and 7, but not 2 and 5, engage the lagging strand with an approximate step size of one base per subunit. Staggered coupling of the two opposing hexamers positions the DNA right in front of the two Mcm2-Mcm5 gates, with each strand being pressed against one gate. The architecture suggests that lagging-strand extrusion initiates in the middle of the DH that is composed of the zinc finger domains of both hexamers. To convert the Mcm2-7 DH structure into the Mcm2-7 hexamer structure found in the active helicase, the N-tier ring of the Mcm2-7 hexamer in the DH-dsDNA needs to tilt and shift laterally. We suggest that these N-tier ring movements cause the DNA strand separation and lagging-strand extrusion.

Item Type: Paper
Uncontrolled Keywords: DNA replication DNA unwinding cryo-electron microscopy helicase mini chromosome maintenance
Subjects: Investigative techniques and equipment > microscopy > Cryo-electron microscopy
bioinformatics > genomics and proteomics > genetics & nucleic acid processing > DNA, RNA structure, function, modification > DNA replication
bioinformatics > genomics and proteomics > genetics & nucleic acid processing > protein structure, function, modification > protein types > enzymes > helicase
CSHL Authors:
Communities: CSHL labs > Stillman lab
CSHL Cancer Center Program > Gene Regulation and Cell Proliferation
Depositing User: Matt Covey
Date: 7 November 2017
Date Deposited: 30 Oct 2017 19:03
Last Modified: 12 Jun 2018 19:22
PMCID: PMC5692578
Related URLs:
URI: http://repository.cshl.edu/id/eprint/35655

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