Stereochemistry of the elongation factor Tu · GTP complex

Abstract

The geometry of the Me2+· GTP complex at the active site of EF‐Tu from Bacillus stearothermophilus has been investigated using thiophosphate analogs of GTP to inhibit the kirromycin‐induced GTPase reaction at 60 mM NH4Cl. There is no reversed selectivity for the diastereomers (Rp and Sp) of guanosine 5′‐O‐(1‐thiotriphosphate) (GTP[αS]) on replacing Mg2+ by Cd2+, so that the observed specifity for the Sp isomer must be due to an interaction of the pro‐R oxygen of the α‐phosphate group with the protein. With the diastereomers of GTP[βS] low specifity for the Rp isomers is seen in the presence of Mg2+. Moreover, both isomers are very weakly bound. In contrast, substitution of Mg2+ by Cd2+ results in a high specifity for the Sp isomer, and this is then recognized as well as Cd · GTP. These results indicate that in the EF‐Tu · Me2+ GTP complex, the pro‐S oxygen of the β‐phosphate group is bound to the metal ion and the pro‐R oxygen to the protein. GTP[γS] is a good analog of GTP regardless of the nature of the metal ion, suggesting that not all of the oxygens of the γ‐phosphate are involved in interactions to metal ion and protein. The thiophosphate analogs of GTP were also tested for their efficiency in ternary complex formation with EF‐Tu and aminoacyl‐tRNA and in the physiological GTPase of EF‐Tu. The stereochemistry of the GTP binding site on EF‐Tu in all three systems is found to be very similar. Copyright © 1983, Wiley Blackwell. All rights reserved