Fluoride inhibition of yeast enolase: crystal structure of the enolase-Mg(2+)-F(-)-Pi complex at 2.6 A resolution.

Enolase in the presence of its physiological cofactor Mg2+ is inhibited by fluoride and phosphate ions in a strongly cooperative manner (Nowak, T, Maurer, P. Biochemistry 20:6901, 1981). The structure of the quaternary complex yeast enolase-Mg(2+)-F(-)-Pi has been determined by X-ray diffraction and refined to an R = 16.9% for those data with F/sigma (F) > or = 3 to 2.6 A resolution with a good geometry of the model. The movable loops of Pro-35-Ala-45, Val-153-Phe-169, and Asp-255-Asn-266 are in the closed conformation found previously in the precatalytic substrate-enzyme complex. Calculations of molecular electrostatic potential show that this conformation stabilizes binding of negatively charged ligands at the Mg2+ ion more strongly than the open conformation observed in the native enolase. This closed conformation is complementary to the transition state, which also has a negatively charged ion, hydroxide, at Mg2+. The synergism of inhibition by F- and Pi most probably is due to the requirement of Pi for the closed conformation. It is possible that other Mg(2+)-dependent enzymes that have OH- ions bound to the metal ion in the transition state also will be inhibited by fluoride ions.