Structure of human Cdc45 and implications for CMG helicase function

Cell division cycle protein 45 (Cdc45) is required for DNA synthesis during genome duplication, as a component of the Cdc45-MCM-GINS (CMG) helicase. Despite its essential biological function, its biochemical role in DNA replication has remained elusive. Here we report the 2.1Å crystal structure of human Cdc45, which confirms its evolutionary link with the bacterial RecJ nuclease and reveals several unexpected features that underpin its function in eukaryotic DNA replication. These include a long-range interaction between N- and C-terminal DHH domains, blocking access to the DNA-binding groove of its RecJ-like fold, and a helical insertion in its N-terminal DHH domain, which appears poised for replisome interactions. In combination with available electron microscopy data, we validate by mutational analysis the mechanism of Cdc45 association with the MCM ring and GINS co-activator, critical for CMG assembly. These findings provide an indispensable molecular basis to rationalise the essential role of Cdc45 in genomic duplication.We would like to thank Ben Luisi for help with X-ray data collection, Alessandro Costa for sharing the cryoEM data of the CMG complex before publication and Joseph Maman for help with the analysis of Cdc45-DNA interactions. This work was supported by a Wellcome Trust Senior Investigator award to LP (104641/Z/14/Z) and a Cambridge Gates PhD scholarship to ACS. VC is funded by the Associazione Italiana per Ricerca sul Cancro (AIRC), the European Research Council (ERC) consolidator grant (614541), the Association for International Cancer Research (AICR), the Giovanni-Armenise award to VC, the Epigen Progetto Bandiera and the Fondazione Telethon.This is the final version of the article. It first appeared from Nature via https://doi.org/10.1038/ncomms1163