ATP-hydrolysis-dependent conformational switch modulates the stability of MutS-mismatch complexes.

The mismatch repair pathway in Escherichia coli has been extensively studied in vitro as well as in vivo. The molecular mechanisms by which nucleotide cofactors regulate the whole process constitute an area of active debate. Here we demonstrate that nucleotide (ADP or ATP) binding to MutS mediates a switch in protein conformation. However, in MutS that is DNA bound, this switch ensues only with ATP and not with ADP and is similar, irrespective of whether it is bound to a homo- or a heteroduplex. The results envisage a minimal model of three confor-mational states of MutS as reflected in: (i) a specific and highly stable MutS-mismatch complex in the absence of a nucleotide; (ii) a specific but less stable complex in the presence of ATP hydrolysis; and (iii) an irreversibly dissociated complex in the presence of ATP binding (ATPgammaS). Such transitions are of relevance to the protein's function in vivo where it has to first recognize a mismatch, followed by a search for hemimethylated sites.