The main role of EF-Tu is clearly in the elongation phase of bacterial protein synthesis. The protein transports aminoacylated tRNA (aa-tRNA) molecules to the programmed ribosome and profoundly contributes to an accurate and fast translation of mRNAs into proteins. EF-Tu was the first protein found to be regulated by the binding and subsequent hydrolysis of GTP, making it a paradigm for the superfamily of regulatory GTPases. The rather loose structure of the GDP complex, originally seen with an EF-Tu that had been proteolytically cleaved at at least two sites, was later validated by X-ray analysis of crystals of intact EF-Tu·GDP. While the mechanism of the ribosome-mediated GTPase reaction of EF-Tu is thus entirely unclear, very little is known about the intrinsic GTP-hydrolyzing activity exhibited by the enzyme in the absence of the ribosome. In the amino acid sequence of EF-Tu, the conserved glutamine residue of Gα and Ras is replaced by His-85. The importance of the hydrophobic gate in protecting the nucleophilic water molecule from premature activation was tested by replacing the wing residues (V20S and I61A mutants). Both mutants do show a somewhat elevated intrinsic GTPase, but instead of His-85 swinging in to activate the nucleophilic water, the authors observe the rearrangement of a chain of water molecules extending from bulk solvent to the γ-phosphate.