Abstract
The Mre11-Rad50 protein complex is an initial responder to sites of DNA double strand breaks. Many studies have shown that ATP binding to Rad50 causes global changes to the Mre11-Rad50 structure, which are important for DNA repair functions. Here we used methyl-based NMR spectroscopy on a series of mutants to describe a dynamic allosteric pathway within Rad50. Mutations result in changes in the side chain methyl group chemical environment that are correlated with altered nanosecond timescale dynamics. We also observe striking relationships between the magnitude of chemical shift perturbations and Rad50 and Mre11 activities. Together, these data suggest an equilibrium between a ground state and an "active" dimerization competent state of Rad50 that has locally altered structure and dynamics and is poised for ATP-induced dimerization and eventual ATP hydrolysis. Thus, this sparsely populated intermediate is critical for Mre11-Rad50-directed DNA double strand break repair.