DNA-tension dependence of restriction enzyme activity reveals mechanochemical properties of the reaction pathway.

Type II restriction endonucleases protect bacteria against phage infections by cleaving recognition sites on foreign double-stranded DNA (dsDNA) with extraordinary specificity. This capability arises primarily from large conformational changes in enzyme and/or DNA upon target sequence recognition. In order to elucidate the connection between the mechanics and the chemistry of DNA recognition and cleavage, we used a single-molecule approach to measure rate changes in the reaction pathway of EcoRV and BamHI as a function of DNA tension. We show that the induced-fit rate of EcoRV is strongly reduced by such tension. In contrast, BamHI is found to be insensitive, providing evidence that both substrate binding and hydrolysis are not influenced by this force. Based on these results, we propose a mechanochemical model of induced-fit reactions on DNA, allowing determination of induced-fit rates and DNA bend angles. Finally, for both enzymes a strongly decreased association rate is obtained on stretched DNA, presumably due to the absence of intradomain dissociation/re-association between non-specific sites (jumping). The obtained results should apply to many other DNA-associated proteins.