The crystal structure of Cys-tRNA(Cys)-EF-Tu-GDPNP reveals general and specific features in the ternary complex and in tRNA

Background: The translation elongation factor EF-Tu in its GTP-bound state forms a ternary complex with any aminoacylated tRNA (aa-tRNA), except initi ator tRNA and selenocysteinyl-tRNA. This complex delivers aa-tRNA to the ri bosomal A site during the elongation cycle of translation, The crystal stru cture of the yeast Phe-tRNA(Phe) ternary complex with Thermus aquaticus EF- Tu-GDPNP (Phe-TC) has previously been determined as one representative of t his general yet highly discriminating complex formation. Results: The ternary complex of Escherichia coli Cys-tRNA(Cys) and T. aquat icus EF-Tu-GDPNP (Cys-TC) has been solved and refined at 2.6 Angstrom resol ution. Conserved and variable features of the aa-tRNA recognition and bindi ng by EF-TU-GTP have been revealed by comparison with the Phe-TC structure. New tertiary interactions are observed in the tRNA(Cys) structure. A 'kiss ing complex' is observed in the very close crystal packing arrangement. Conclusions: The recognition of Cys-tRNA(Cys) by EF-Tu-GDPNP is restricted to the aa-tRNA motif previously identified in Phe-TC and consists of the am inoacylated 3' end, the phosphorylated 5' end and one side of the acceptor stem and T stem. The aminoacyl bond is recognized somewhat differently, yet by the same primary motif in EF-Tu, which suggests that EF-Tu adapts to su btle variations in this moiety among all aa-tRNAs, New tertiary interaction s revealed by the Cys-tRNA(Cys) structure, such as a protonated C16:C59 pyr imidine pair, a G15:G48 'Levitt pair' and an s(4)U8:A14:A46 base triple add to the generic understanding of tRNA structure from sequence. The structur e of the 'kissing complex' shows a quasicontinuous helix with a distinct sh ape determined by the number of base pairs.