Identification of a topoisomerase IV in actinobacteria:: purification and characterization of ParYR and GyrBR from the coumermycin A1 producer Streptomyces rishiriensis DSM 40489

The biosynthetic gene clusters of the gyrase inhibitors coumermycin A(1) and clorobiocin contain two different resistance genes (gyrB(R) and parY(R)). Both genes code for B subunits of type II topoisomerases. The authors have now over expressed and purified the encoded proteins, as well as the corresponding A subunits GyrA and ParX. Expression was carried out in Streptomyces lividans in the form of hexahistidine fusion proteins, allowing purification by nickel affinity chromatography. The complex of GyrA and GyrB(R) was found to catalyse ATP-dependent supercoiling of DNA, i.e. to function as a gyrase, whereas the complex of ParX and ParY(R) catalysed ATP-dependent decatenation and relaxation, i.e. the functions of topoisomerase IV (topo IV). This is believed to represent the first topo IV identified in the class of actinobacteria, and the first demonstration of the formation of a topo IV as a resistance mechanism of an antibiotic producer.