| DNA mismatch repair (MMR) protects the integrity of the genome by correcting mismatches that occur in DNA as a result of errors arising during replication and recombination. MutS proteins initiate DNA repair by recognizing the mismatch, and trigger a series of repair events that result in excision and resynthesis of the incorrect DNA strand. MutS proteins possess an ATPase activity that is essential for their repair function. A thorough understanding of MutS function requires knowledge of how the ATPase mechanism is coupled to mismatch recognition and initiation of repair. Kinetic analysis of T. aquaticus MutS and S. cerevisiae Msh2-Msh6 protein activity has revealed key conserved features of their mechanism of action; (a) the subunits in the MutS dimer bind and hydrolyze ATP asymmetrically, with one binding ATP with high affinity and hydrolyzing it rapidly---at up to 30-fold faster rates than the other; (b) MutS interaction with mismatched DNA alters the ATPase kinetics by suppressing rapid ATP hydrolysis, such that the protein-DNA complex is stabilized in an ATP-bound state; (c) Stable ATP binding to both MutS subunits alters the interaction between the protein and DNA, likely leading to downstream events in the DNA repair pathway. This work also illustrates the utility of rapid kinetic analysis for investigating the mechanism of action of different ATP-utilizing proteins, with a short study of the E. coli SecA protein translocase. |
