The Structure of the EF‐Tu · GDP · Me2+ Complex

Abstract

The structure of the MgGDP complex at the active site of elongation factor (EF‐Tu) has been investigated by using phosphorothioate analogs of GDP in the absence and presence of various metal ions, electron para‐magnetic resonance (EPR) and nuclear magnetic resonance (NMR) measurements. The high stereoselectivity of EF‐Tu for the diastereomers of guanosine 5′‐0‐(1‐thiodiphosphate) (GDP[αS]) is independent of the nature of the metal ion and is caused by the interaction of the protein with the α‐phosphate of GDP. By using GDP analogs where the oxygens at either thea‐phosphate or thep‐phosphate have been selectively labelled with 17O and measuring their effect on the EPR spectrum of EF‐Tu‐bound manganese we are able to show that only the β‐phosphate of GDP is coordinated to the metal ion in the EF‐Tu. Me2+. GDPcomplex. 31P‐NMR studies on GDP and guanosine 5′‐0‐(2‐thiodiphosphate) (GDP[βS]) bound to EF‐Tu indicate that in the EF‐Tu Me2+ GDP complex Mg2+ interacts more strongly with the β‐phosphate than with the α‐phosphate. Together with binding studies using GDP[βS] our NMR results also indicate that the protein is complexed to the β‐phosphorous of GDP via two oxygens. Copyright © 1982, Wiley Blackwell. All rights reserved