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bioRxiv · 10.1101/2025.05.31.656953

Cryo-EM structure of DNA-unbound human MCM2-7 complex reveals new disease-relevant regulation

Liu, Y.·Yang, M.·Lu, P.·Gao, H.·He, M.·Wang, Y.·Qi, A.·Cao, T.·Zhang, Q.·Qi, S.·Shi, Y.·Yu, H.
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Abstract

Chromatin loading of the hexameric replicative helicase MCM2-7 complex requires coordinated interactions with the origin recognition complex (ORC), CDC6, and CDT1. MCM2-7 not bound to DNA forms a single hexamer (SH) with an open DNA entry gate. Two MCM2-7 SHs are loaded sequentially to form the double hexamer (DH) that encircles the DNA duplex. Activated MCM2-7 then unwinds DNA and initiates DNA replication. Our cryo-electron microscopy analyses show that a fraction of human MCM2-7 without DNA exists as DH. Unexpectedly, we find that the MCM3 winged helix domain (WHD) docks on MCM2 in both DNA-free DH and SH, creating a safety latch across the DNA entry gate to block DNA entry into the central channel. The safety latch can be opened by ORC-CDC6 binding. Disrupting this latch by designed or human disease-related mutations of MCM3 causes replication defects and DNA damage checkpoint activation. Our findings uncover a new regulated step in MCM2-7 loading with implications for human diseases.

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Liu, Y., Yang, M., Lu, P., Gao, H., He, M., Wang, Y., Qi, A., Cao, T., Zhang, Q., Qi, S., Shi, Y., Yu, H.. 2025-06-03. Cryo-EM structure of DNA-unbound human MCM2-7 complex reveals new disease-relevant regulation. https://doi.org/10.1101/2025.05.31.656953

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