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Biochim Biophys Acta. 2011 May;1814(5):684-92. doi: 10.1016/j.bbapap.2011.02.007. Epub 2011 Feb 19.

Construction of a fully active Cys-less elongation factor Tu: functional role of conserved cysteine 81.

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Department of Chemistry and Biochemistry, University of Lethbridge, Lethbridge, Canada.


In order to study the structural and functional requirements of the essential translational GTPase elongation factor (EF) Tu for efficient and accurate ribosome-dependent protein synthesis, construction of a cysteine-free (Cys-less) mutant variant allowing for the site-directed introduction of fluorescent and non-fluorescent labels is of great importance. However, previous reports suggest that a cysteine residue in position 81 of EF-Tu from Escherichia coli is essential for its function. To study the functional role of cysteine 81 and to construct a fully active Cys-less EF-Tu, we have analyzed 125 bacterial sequences with respect to sequence variations in this position revealing that in a small number of sequences alanine and methionine can be found. Here we report the detailed comparative biochemical analysis of three Cys-less variants of EF-Tu containing these substitutions as well as the isosteric amino acid serine. By characterizing nucleotide binding, EF-Ts interaction, aminoacyl-tRNA binding, and delivery to the ribosome, we demonstrate that only alanine (or cysteine) can be tolerated in this position and that the serine and methionine substitutions significantly impair aminoacyl-tRNA, but not nucleotide binding. Our findings suggest a critical functional role of the amino acid residue in position 81 of EF-Tu with respect to aminoacyl-tRNA binding. Based on structural considerations, we suggest that position 81 indirectly contributes to aminoacyl-tRNA binding through the accurate positioning of helix B.

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