Fluoroaluminates do not affect the guanine-nucleotide binding centre of the peptide chain elongation factor EF-Tu

EF-Tu is often referred to as a model for guanine-nucleotide-binding regulatory proteins (G-proteins), since X-ray diffraction analysis of its GTP-binding domain shows a detailed location of the 'consensus' amino acid sequences involved in nucleotide binding. Fluoroaluminates are thought to mimick the gamma-phosphate in the GTPase centre on account of their activating effect on a variety of GTP binding proteins. In the case of EF-Tu, we could find no such effects on the basis of at least three independent functional assays. We did notice, however, complicating interactions between free nucleotides, fluoroaluminates and other ligands. By consequence, if indeed AlF4- behaves as a gamma-phosphate analogue in G-proteins, then EF-Tu must have a different GDP/GTP binding site, despite of the conserved consensus sequences.