The crystal structure of Sulfolobus solfataricus elongation factor 1 alphain complex with GDP reveals novel features in nucleotide binding and exchange

The crystal structure of elongation factor 1 alpha from the archaeon Sulfol obus solfataricus in complex with GDP (SsEF-1 alpha .GDP) at 1.8 Angstrom r esolution is reported. As already known for the eubacterial elongation fact or Tu, the SsEF-1 alpha .GDP structure consists of three different structur al domains. Surprisingly, the analysis of the GDP-binding site reveals that the nucleotide-protein interactions are not mediated by Mg2+. Furthermore, the residues that usually co-ordinate Mg2+ through water molecules in the GTP-binding proteins, though conserved in SsEF-1 alpha, are located quite f ar from the binding site. [H-3]GDP binding experiments confirm that Mg2+ ha s only a marginal effect on the nucleotide exchange reaction of SsEF-1 alph a, although essential to GTPase activity elicited by SsEF-1 alpha Finally, structural comparisons of SsEF1 alpha -GDP with yeast EF-la in complex with the nucleotide exchange factor EF-1 beta shows that a dramatic rearrangeme nt of the overall structure of EF-1 alpha occurs during the nucleotide exch ange.