FLUORIDE INHIBITION OF YEAST ENOLASE - CRYSTAL-STRUCTURE OF THE ENOLASE-MG2+-F--PI COMPLEX AT 2.6 ANGSTROM 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-Mg2+-F-P(i) has been determined by X-ray diffraction and refined to an R = 16.9% for those data with F/sigma(F) greater-than-or-equal-to 3 to 2.6 angstrom 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 P(i) most probably is due to the requirement of P(i) for the closed conformation. It is possible that other Mg2+-dependent enzymes that have OH- ions bound to the metal ion in the transition state also will be inhibited by fluoride ions.