The dynamic nature of the human origin recognition complex revealed through five cryoEM structures

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• Genome replication initiation relies on the Origin Recognition Complex (ORC).
• ORC orchestrates DNA replication by binding origin DNA and recruiting key proteins.
• Understanding ORC structure and dynamics is vital for comprehending replication control.

Purpose of the Study:

• To elucidate the structural dynamics of the human ORC (HsORC).
• To investigate the role of ORC subunits, particularly ORC1, in complex conformation.
• To compare human ORC-DNA interactions with those in yeast.

Main Methods:

• Utilized cryo-electron microscopy (cryo-EM) to determine five distinct HsORC structures.
• Analyzed structures with and without the ORC1 subunit.
• Examined HsORC bound to endogenous DNA.

Main Results:

• HsORC displays significant native flexibility, with ORC1 influencing its conformation.
• Identified dynamic movements in ORC1 and ORC2 domains affecting DNA binding.
• Revealed a hinge at the ORC5·ORC3 interface facilitating DNA interaction.
• Observed distinct human ORC-DNA binding compared to yeast.

Conclusions:

• Human ORC flexibility is essential for its function in initiating DNA replication.
• Structural dynamics of HsORC subunits regulate DNA engagement.
• Cryo-EM provides critical insights into human origin recognition mechanisms.