Heteroduplex DNA and ATP induced conformational changes of a MutS mismatch repair protein from Thermus aquaticus.

ATP hydrolysis by MutS homologues is required for the function of these proteins in mismatch repair. However, the function of ATP hydrolysis in the repair reaction is not very clear. We have examined the role of ATP hydrolysis in oligomerization of Thermus aquaticus (Taq) MutS protein in solution. Analytical gel filtration and cross-linking of MutS protein with disuccinimidyl suburate suggest that TaqMutS is a dimer in the presence of ATP. ATP binding and hydrolysis by TaqMutS reduces the heteroduplex-DNA binding by the protein. Using limited proteolysis we detected extensive conformational changes of the TaqMutS protein in the presence of ATP and heteroduplex DNA. Heteroduplex-DNA binding is necessary for the observed conformational changes since F39A mutant protein defective in DNA binding does not display ATP-induced conformational changes. The implications of the observed conformational changes in the MutS protein are discussed with respect to two different models proposed for the role of ATP hydrolysis by MutS in DNA mismatch repair.