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

The crystal structure of elongation factor 1α from the archaeon Sulfolobus solfataricus in complex with GDP (SsEF-1α⋅GDP) at 1.8 Å resolution is reported. As already known for the eubacterial elongation factor Tu, the SsEF-1α⋅GDP structure consists of three different structural domains. Surprisingly, the analysis of the GDP-binding site reveals that the nucleotide– protein interactions are not mediated by Mg(2+). Furthermore, the residues that usually co-ordinate Mg(2+) through water molecules in the GTP-binding proteins, though conserved in SsEF-1α, are located quite far from the binding site. [(3)H]GDP binding experiments confirm that Mg(2+) has only a marginal effect on the nucleotide exchange reaction of SsEF-1α, although essential to GTPase activity elicited by SsEF-1α. Finally, structural comparisons of SsEF- 1α⋅GDP with yeast EF-1α in complex with the nucleotide exchange factor EF-1β shows that a dramatic rearrangement of the overall structure of EF-1α occurs during the nucleotide exchange.