Characterization and structure determination of the Cdt1 binding domain of human minichromosome maintenance (Mcm) 6.

The minichromosome maintenance (Mcm) 2-7 complex is the replicative helicase in eukaryotic species, and it plays essential roles in the initiation and elongation phases of DNA replication. During late M and early G(1), the Mcm2-7 complex is loaded onto chromatin to form prereplicative complex in a Cdt1-dependent manner. However, the detailed molecular mechanism of this loading process is still elusive. In this study, we demonstrate that the previously uncharacterized C-terminal domain of human Mcm6 is the Cdt1 binding domain (CBD) and present its high resolution NMR structure. The structure of CBD exhibits a typical "winged helix" fold that is generally involved in protein-nucleic acid interaction. Nevertheless, the CBD failed to interact with DNA in our studies, indicating that it is specific for protein-protein interaction. The CBD-Cdt1 interaction involves the helix-turn-helix motif of CBD. The results reported here provide insight into the molecular mechanism of Mcm2-7 chromatin loading and prereplicative complex assembly.