THE STRUCTURE OF EF-Tu^.EF-Ts COMPLEX SUGGESTS A MECHANISM FOR NUCLEOTIDE RELEASE. Takemasa Kawashima, Carmen Berthet-Colominas, Michael Wulff*, Stephen Cusack and Reuben Leberman, EMBL Grenoble Outstation B.P. 156, 38042 Grenoble Cedex, France, *European Synchrotron Radiation Facility, B.P 220, 38043 Grenoble Cedex, France.

The crystal structure of the bacterial elongation factor complex EF-Tu^.EF-Ts from Escherichia coli has been determined at 2.5 Å resolution. It reveals a typical guanine nucleotide binding protein in interaction with its guanine nucleotide release factor. The complex is a tetramer where two EF-Ts form a tight dimer and each EF-Tu binds essentially to one EF-Ts, with barely any contact between EF-Tu, such that the complex is best described by the formula EF-Tu^.(EF-Ts)₂.EF-Tu. Comparison of EF-Tu^.GDP and EF-Tu^.EF-Ts shows that the conformational change between the two structures mainly alters the magnsium binding site, by disrupting the coordination of the ion. This suggests a molecular mechanism by which EF-Ts releases the GDP bound to EF-Tu where the affinity of EF-Tu for GDP is lowered by the loss of the magnesium ion.

Kawashima, T., Berthet-Colominas, C., Wulff, M., Cusack, S. and Leberman, R. Nature 379, 511-518 (1996).