8var
Structure of the E. coli clamp loader bound to the beta clamp in a Closed-DNA2 conformation
Structural highlights
FunctionDPO3B_ECOLI DNA polymerase III is a complex, multichain enzyme responsible for most of the replicative synthesis in bacteria. This DNA polymerase also exhibits 3' to 5' exonuclease activity. The beta chain is required for initiation of replication once it is clamped onto DNA, it slides freely (bidirectional and ATP-independent) along duplex DNA. Publication Abstract from PubMedClamp loaders are pentameric ATPases that place circular sliding clamps onto DNA, where they function in DNA replication and genome integrity. The central activity of a clamp loader is the opening of the ring-shaped sliding clamp and the subsequent binding to primer-template (p/t)-junctions. The general architecture of clamp loaders is conserved across all life, suggesting that their mechanism is retained. Recent structural studies of the eukaryotic clamp loader replication factor C (RFC) revealed that it functions using a crab-claw mechanism, where clamp opening is coupled to a massive conformational change in the loader. Here we investigate the clamp loading mechanism of the Escherichia coli clamp loader at high resolution using cryo-electron microscopy. We find that the E. coli clamp loader opens the clamp using a crab-claw motion at a single pivot point, whereas the eukaryotic RFC loader uses motions distributed across the complex. Furthermore, we find clamp opening occurs in multiple steps, starting with a partly open state with a spiral conformation, and proceeding to a wide open clamp in a surprising planar geometry. Finally, our structures in the presence of p/t-junctions illustrate how the clamp closes around p/t-junctions and how the clamp loader initiates release from the loaded clamp. Our results reveal mechanistic distinctions in a macromolecular machine that is conserved across all domains of life. Differences between bacteria and eukaryotes in clamp loader mechanism, a conserved process underlying DNA replication.,Landeck JT, Pajak J, Norman EK, Sedivy EL, Kelch BA J Biol Chem. 2024 Apr;300(4):107166. doi: 10.1016/j.jbc.2024.107166. Epub 2024 , Mar 14. PMID:38490435[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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