Escherichia coli processivity clamp beta from DNA polymerase III is dynamic in solution

摘要

beta clamp is not a static closed ring but rather has significant dynamics in solution. The dimer interface of the beta clamp may open spontaneously. Domain I, which may control the opening of the clamp by dissociating from Domain III, contained several highly flexible peptides which underwent an obvious partial unfolding event (EX1 kinetics) with a half-life approx 4 h. The beta monomer was more flexible than the WT beta clamp. Unfolding kinetics were much faster in the monomer and additional peptides in Domain III of beta monomer also displayed EX1 kinetics, with an unfolding half-life approx 1h. The delta subunit of the clamp loader may function as a "ring holder" to stabilize the transient opening of the beta clamp, rather than as a "ring opener".