Cdt1 stabilizes an open MCM ring for helicase loading

• DOI: 10.1038/ncomms15720
• Publication Date: 2017-06-23T09:46:47Z
• Authors: Jordi Frigola; Jun He; Kerstin Kinkelin; Valerie E. Pye; Ludovic Renault; Max E. Douglas; Dirk Remus; Peter Cherepanov; Alessandro Costa; John F. X. Diffley
• Keywords: STRUCTURAL BASIS; DNA Replication; Models, Molecular; 0301 basic medicine; 570; BUDDING YEAST; Saccharomyces cerevisiae Proteins; Protein Conformation; Science; DOUBLE-HEXAMER; Origin Recognition Complex; 610; Cell Cycle Proteins; Replication Origin; Saccharomyces cerevisiae; Crystallography, X-Ray; Article; 03 medical and health sciences; Adenosine Triphosphate; Protein Domains; MD Multidisciplinary; Electron microscopy; CRYO-EM STRUCTURE; DNA, Fungal; ELECTRON-MICROSCOPY; Science & Technology; COMPLEX; NUCLEAR ACCUMULATION; Minichromosome Maintenance Proteins; ORIGIN; Hydrolysis; EUKARYOTIC DNA-REPLICATION; Q; DNA Helicases; DNA; ATP HYDROLYSIS; Multidisciplinary Sciences; DNA-Binding Proteins; Microscopy, Electron; Cross-Linking Reagents; Science & Technology - Other Topics; Replisome

AbstractORC, Cdc6 and Cdt1 act together to load hexameric MCM, the motor of the eukaryotic replicative helicase, into double hexamers at replication origins. Here we show that Cdt1 interacts with MCM subunits Mcm2, 4 and 6, which both destabilizes the Mcm2–5 interface and inhibits MCM ATPase activity. Using X-ray crystallography, we show that Cdt1 contains two winged-helix domains in the C-terminal half of the protein and a catalytically inactive dioxygenase-related N-terminal domain, which is important for MCM loading, but not for subsequent replication. We used these structures together with single-particle electron microscopy to generate three-dimensional models of MCM complexes. These show that Cdt1 stabilizes MCM in a left-handed spiral open at the Mcm2–5 gate. We propose that Cdt1 acts as a brace, holding MCM open for DNA entry and bound to ATP until ORC–Cdc6 triggers ATP hydrolysis by MCM, promoting both Cdt1 ejection and MCM ring closure.