Adenosine 5′-O-(3-thio)triphosphate (ATPγS) Promotes Positive Supercoiling of DNA by T. maritima Reverse Gyrase

Abstract

Reverse gyrases are topoisomerases that catalyze ATP-dependent positive supercoiling of circular covalently closed DNA. They consist of an N-terminal helicase-like domain, fused to a C-terminal topoisomerase I-like domain. Most of our knowledge on reverse gyrase-mediated positive DNA supercoiling is based on studies of archaeal enzymes. To identify general and individual properties of reverse gyrases, we set out to characterize the reverse gyrase from a hyperthermophilic eubacterium . Thermotoga maritima reverse gyrase relaxes negatively supercoiled DNA in the presence of ADP or the non-hydrolyzable ATP-analog ADPNP. Nucleotide binding is necessary, but not sufficient for the relaxation reaction. In the presence of ATP, positive supercoils are introduced at temperatures above 50 °C. However, ATP hydrolysis is stimulated by DNA already at 37 °C, suggesting that reverse gyrase is not frozen at this temperature, but capable of undergoing inter-domain communication. Positive supercoiling by reverse gyrase is strictly coupled to ATP hydrolysis. At the physiological temperature of 75 °C, reverse gyrase binds and hydrolyzes ATPγS. Surprisingly, ATPγS hydrolysis is stimulated by DNA, and efficiently promotes positive DNA supercoiling, demonstrating that inter-domain communication during positive supercoiling is fully functional with both ATP and ATPγS. These findings support a model for communication between helicase-like and topoisomerase domains in reverse gyrase, in which an ATP and DNA-induced closure of the cleft in the helicase-like domain initiates a cycle of conformational changes that leads to positive DNA supercoiling.