Nucleotide-Induced Conformational Changes in an Isolated Escherichia coli DNA Polymerase III Clamp Loader Subunit

AbstractSliding clamps are loaded onto DNA by ATP-driven clamp loader complexes. The structure of the E. coli clamp loader in a nucleotide-free state has been determined previously. We now report crystal structures of a truncated form of the isolated γ-ATPase subunit, γ1–243, of the E. coli clamp loader, in nucleotide-free and bound forms. The γ subunit adopts a defined conformation when empty, in which the nucleotide binding site is blocked. The binding of either ATPγS or ADP, which are shown to bind with equal affinity to γ1–243, induces a change in the relative orientation of the two domains such that nucleotides can be accommodated. This change would break one of the γ:γ interfaces seen in the empty clamp loader complex, and may represent one step in the activation process