Research ArticleBIOCHEMISTRY

Activation of GTP hydrolysis in mRNA-tRNA translocation by elongation factor G

Science Advances  22 May 2015:
Vol. 1, no. 4, e1500169
DOI: 10.1126/sciadv.1500169

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Abstract

During protein synthesis, elongation of the polypeptide chain by each amino acid is followed by a translocation step in which mRNA and transfer RNA (tRNA) are advanced by one codon. This crucial step is catalyzed by elongation factor G (EF-G), a guanosine triphosphatase (GTPase), and accompanied by a rotation between the two ribosomal subunits. A mutant of EF-G, H91A, renders the factor impaired in guanosine triphosphate (GTP) hydrolysis and thereby stabilizes it on the ribosome. We use cryogenic electron microscopy (cryo-EM) at near-atomic resolution to investigate two complexes formed by EF-G H91A in its GTP state with the ribosome, distinguished by the presence or absence of the intersubunit rotation. Comparison of these two structures argues in favor of a direct role of the conserved histidine in the switch II loop of EF-G in GTPase activation, and explains why GTP hydrolysis cannot proceed with EF-G bound to the unrotated form of the ribosome.

Keywords
  • Cryo-EM
  • Ribosome
  • translocation
  • Elongation factor G
  • GTP hydrolysis

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