Nucleotide-dependent conformational changes in the DnaA-like core of the origin recognition complex

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• DNA replication is a fundamental biological process initiated by initiator proteins.
• The origin recognition complex (ORC) is a key initiator in eukaryotes.
• Understanding ORC structure and function is crucial for elucidating replication mechanisms.

Purpose of the Study:

• To investigate the structural basis of nucleotide-dependent conformational changes in the Drosophila melanogaster origin recognition complex (ORC).
• To compare the structural features of ORC with prokaryotic initiator proteins like DnaA.
• To propose a model for how ORC prepares DNA for replication initiation.

Main Methods:

• Electron microscopy (EM) reconstructions of the Drosophila melanogaster ORC.
• Comparative structural analysis of AAA+ domains in ORC and DnaA.
• Computational docking of DnaA into the ORC structure.

Main Results:

• EM reconstructions revealed nucleotide-dependent conformational changes in the core of ORC.
• A conserved structural element in ORC's AAA+ domains, similar to DnaA, suggests potential helical substructures in initiators.
• A DnaA helical pentamer could be docked into ORC, with Orc5 uniquely positioning this core.
• ATP-dependent conformational changes in ORC are likely due to reorientation of its AAA+ domains.

Conclusions:

• Conserved helical AAA+ substructures may be a common feature of DNA replication initiators.
• ORC's conformational changes are driven by AAA+ domain reorientation.
• ORC and Cdc6 likely prepare origin DNA for helicase loading via mechanisms analogous to prokaryotic pathways.