The Binding of Kirromycin to Elongation Factor Tu

Abstract

The influence of kirromycin [from Streptomyces collinus] on the elongation factor Tu (EF-Tu) [from Escherichia coli] in its binary and ternary complexes was investigated. The equilibrium constant for the binding of the antibiotic to EF-Tu.cntdot.GDP and EF-Tu.cntdot.GTP was determined by circular dichroism [CD] titrations to be 4 .times. 106 M-1, and to EF-Tu.cntdot.GTP.cntdot.aa[aminoacyl]-tRNA by a combination of CD titrations and hydrolysis protection experiments to be 2 .times. 106 M-1. In the presence of kirromycin the binding of aa-tRNA to EF-Tu.cntdot.GTP is weakened by a factor of two. The antibiotic changes the conformation of the ternary complex in such a way that the aa moiety of the aa-tRNA is more accessible to the non-enzymatic hydrolysis. This structural alteration is apparently responsible for the inhibitory action of the antibiotic.