Stabilisation of half MCM ring by Cdt1 during DNA insertion

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Eukaryotic DNA replication requires precise control to ensure once-per-cell-cycle duplication.
• The Origin Recognition Complex (ORC), Cdc6, and Cdt1 are crucial for loading the Mcm2-7 helicase (MCM) onto DNA at replication origins.
• The mechanism of DNA insertion into the pre-helicase loading complex remains incompletely understood.

Purpose of the Study:

• To elucidate the mechanism of DNA insertion into the eukaryotic replicative helicase.
• To identify the structural components and interactions essential for stable helicase loading.
• To investigate the role of Cdt1's C-terminal winged helix domain (C-WHD) in MCM complex stability and DNA engagement.

Main Methods:

• Structural analysis of protein-DNA complexes.
• Biochemical assays to assess helicase loading and stability.
• Mutational analysis of Cdt1 and Mcm6 C-terminal domains.

Main Results:

• DNA insertion into the stacked OC-MCM-Cdt1 complex presents a topological challenge.
• The C-terminal winged helix domain (C-WHD) of Cdt1 is essential for MCM stability, preventing its dissociation.
• Cdt1-C-WHD interacts with Mcm6-C-WHD, and Orc5 AAA-lid, stabilizing the entire complex during DNA loading.

Conclusions:

• The C-terminal winged helix domain of Cdt1 plays a critical role in stabilizing the Mcm2-7 helicase during DNA loading.
• A conserved interaction network involving Cdt1, Mcm6, and Orc5 orchestrates synchronized events for DNA insertion.
• This study reveals key insights into the intricate mechanism of eukaryotic replicative helicase assembly and activation.