Capreomycin and hygromycin B modulate the catalytic activity of the delta ribozyme in a manner that depends on the protonation and complexation with Cu2+ ions of these antibiotics†
Abstract
Catalytic RNA molecules (ribozymes) have often been used for the testing of interactions of antibiotics with ribonucleic acids. We showed that the impact of capreomycin and hygromycin B on delta ribozyme catalysis might change dramatically, from stimulation to inhibition, depending on conditions. In order to evaluate possible mechanisms of modulation of the ribozyme catalytic activity we used our earlier data on species distribution for protonated forms of capreomycin and hygromycin B and their complexes with Cu2+ ions at different pH values. We proposed that, upon inhibition, the protonated amino group of capreomycin was located in the ribozyme catalytic cleft interfering with binding catalytic Mg2+. Such a mechanism was also supported by the results of ribozyme inhibition with capreomycin complexed with Cu2+. The effects of stimulation of the delta ribozyme activity by capreomycin and hygromycin B were less pronounced than inhibition. Possibly, the amino functions of these antibiotics might be involved in a general acid–base catalysis performed by the ribozyme, acting as proton acceptors/donors.