Two short peptides including segments of subunit A of Escherichia coli DNAgyrase as potential probes to evaluate the antibacterial activity of quinolones

Quinolones constitute a family of compounds with a potent antibiotic activi ty. The enzyme DNA gyrase, responsible for the replication and transcriptio n processes in DNA of bacteria, is involved in the mechanism of action of t hese dugs. In this sense, it is believed that quinolones stabilize the so-c alled 'cleavable complex' formed by DNA and gyrase, but the whole process i s still far from being understood at the molecular level. This information is crucial in order to design new biological active products. As an approac h to the problem, we have designed and synthesized low molecular weight pep tide mimics of DNA gyrase. These peptides correspond to sequences of the su bunit A of the enzyme from Escherichia coil, that include the quinolone res istance-determining region (positions 75-92) and a segment containing the c atalytic Tyr-122 (positions 116-130), The peptide mimic of the non-mutated enzyme binds to ciprofloxin (CFX) only when DNA and Mg2+ were present (K-d = 1.6 x 10(-6) M), a result previously found with DNA gyrase. On the other hand, binding was reduced when mutations of Ser-83 to Leu-83 and Asp-87 to Asn-87 were introduced, a double change previously found in the subunit A o f DNA gyrase from several CFX-resistant clinical isolates of E, coli, These results suggest that synthetic peptides designed in a similar way to that described here can be used as mimics of gyrases (topoisomerases) in order t o study the binding of the quinolone to the enzyme-DNA complex as well as t he mechanism of action of these antibiotics. Copyright (C) 2001 European Pe ptide Society and John Wiley & Sons, Ltd.