Distinct MutS DNA-binding modes that are differentially modulated by ATP binding and hydrolysis

The role of MutS ATPase in mismatch repair is controversial. To clarify fur ther the function of this activity, we have examined adenine nucleotide eff ects on interactions of Escherichia coli MutS with homoduplex and heterodup lex DNAs. In contrast to previous results with human MutS alpha, we find th at a physical block at one end of a linear heteroduplex is sufficient to su pport stable MutS complex formation in the presence of ATP(.)Mg(2+). Surfac e plasmon resonance analysis at low ionic strength indicates that the lifet ime of MutS complexes with heteroduplex DNA depends on the nature of the nu cleotide present when MutS binds. Whereas complexes prepared in the absence of nucleotide or in the presence of ADP undergo rapid dissociation upon ch allenge with ATP(.)Mg(2+), complexes produced in the presence of ATP(.)Mg(2 +), adenosine 5 '-(beta,gamma -imino)triphosphate (AMPPNP)Mg-.(2+), or ATP (no Mg2+) are resistant to dissociation upon ATP challenge. AMPPNP(.)Mg(2+) and ATP (no Mg2+) reduce MutS affinity for heteroduplex but have little ef fect on homoduplex affinity, resulting in abolition of specificity for misp aired DNA at physiological salt concentrations. Conversely, the highest mis match specificity is observed in the absence of nucleotide or in the presen ce of ADP. ADP has only a limited effect on heteroduplex affinity but reduc es MutS affinity for homoduplex DNA.