Reverse gyrase mechanism

Finally, the composite helicase-topoisomerase structure of reverse gyrase suggests that this unusual enzyme could also be involved in any one of the mechanisms which requires the concerted action of such activities [Duguet, M., personal communication]. 

This chapter describes the purification of reverse gyrases from their natural hosts and from recombinant Escherichia coli strains, in addition to the various assays developed to test their biochemical properties. Finally, the main structural features of these enzymes and their putative mechanism are discussed, together with their possible in vivo functions. 

Reverse gyrases, and other topoisomerases, are not typical enzymes, for several reasons (i) the substrate itself, the double helix of DNA, is a macromolecule and has limited diffusion and mobility (ii) as the reaction proceeds, the structure of the substrate, and consequently its affinity for the enzyme, changes (see below) (iii) reverse gyrases not only catalyze chemical reactions, such as transesterifications (Fig. 1) and ATP hydrolysis, but also mechanical actions, such as DNA unwinding and DNA strand passage. 

The unique enzymatic activity of reverses gyrases, i.e., the efficient production of positively supercoiled DNA, was used by a number of authors to estimate the impact of such a DNA structure on various biological mechanisms. These include chromatin stability,recombination, and transcription. However, the in vivo role of reverse gyrases in hyperthermophiles remains a matter of speculation. It was suggested long ago that one of the main functions of topoisomerases is to tightly... 

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