9CAQ

Cryo-EM structure of a human MCM2-7 double hexamer formed from independently loaded MCM2-7 single hexamers

This is a non-PDB format compatible entry.

Summary for 9CAQ

• Entry DOI: 10.2210/pdb9caq/pdb
• Related: 8W0E 8W0F 8W0G 8W0I
• EMDB information: 45400
• Descriptor: DNA replication licensing factor MCM2, MAGNESIUM ION, ADENOSINE-5'-TRIPHOSPHATE, ... (12 entities in total)
• Functional Keywords: complex, helicase, replication, aaa+ atpase
• Biological source: Homo sapiens (human); More
• Total number of polymer chains: 14
• Total formula weight: 1126822.77

Authors

Yang, R.,Hunker, O.,Bleichert, F. (deposition date: 2024-06-17, release date: 2024-10-02, Last modification date: 2024-12-25)

Primary citation

Yang, R.,Hunker, O.,Wise, M.,Bleichert, F.
Multiple mechanisms for licensing human replication origins.
Nature, 636:488-498, 2024

PubMed Abstract: Loading of replicative helicases is obligatory for the assembly of DNA replication machineries. The eukaryotic MCM2-7 replicative helicase motor is deposited onto DNA by the origin recognition complex (ORC) and co-loader proteins as a head-to-head double hexamer to license replication origins. Although extensively studied in budding yeast, the mechanisms of origin licensing in multicellular eukaryotes remain poorly defined. Here we use biochemical reconstitution and electron microscopy to reconstruct the human MCM loading pathway. We find that unlike in yeast, the ORC6 subunit of the ORC is not essential for-but enhances-human MCM loading. Electron microscopy analyses identify several intermediates en route to MCM double hexamer formation in the presence and absence of ORC6, including a DNA-loaded, closed-ring MCM single hexamer intermediate that can mature into a head-to-head double hexamer through multiple mechanisms. ORC6 and ORC3 facilitate the recruitment of the ORC to the dimerization interface of the first hexamer into MCM-ORC (MO) complexes that are distinct from the yeast MO complex and may orient the ORC for second MCM hexamer loading. Additionally, MCM double hexamer formation can proceed through dimerization of independently loaded MCM single hexamers, promoted by a propensity of human MCM2-7 hexamers to self-dimerize. This flexibility in human MCM loading may provide resilience against cellular replication stress, and the reconstitution system will enable studies addressing outstanding questions regarding DNA replication initiation and replication-coupled events in the future.

PubMed: 39604729
DOI: 10.1038/s41586-024-08237-8

Experimental method

ELECTRON MICROSCOPY (3.2 Å)