Structure of bovine mitochondrial F-1-ATPase inhibited by Mg(2+)ADP and aluminium fluoride

Background: The globular domain of the membrane-associated F1Fo-ATP synthas e complex can be detached intact as a water-soluble fragment known as F-1-A TPase. It consists of five different subunits, alpha, beta, gamma, delta an d epsilon, assembled with the stoichiometry 3:3:1:1:1. In the crystal struc ture of bovine F1-ATPase determined previously at 2.8 Angstrom resolution, the three catalytic beta subunits and the three noncatalytic a subunits are arranged alternately around a central alpha-helical coiled coil in the gam ma subunit, In the crystals, the catalytic sites have different nucleotide occupancies. One contains the triphosphate form of the nucleotide, the seco nd contains the diphosphate, and the third is unoccupied. Fluoroaluminate c omplexes have been shown to mimic the transition State in several ATP and G TP hydrolases. In order to understand more about its catalytic mechanism, F -1-ATPase was inhibited with Mg(2+)ADP and aluminium fluoride and the struc ture of the inhibited complex was determined by X-ray crystallography. Results: The structure of bovine F-1-ATPase inhibited with Mg(2+)ADP and al uminium fluoride determined at 2.5 a resolution differs little from the ori ginal structure with bound AMP-PNP and ADP. The nucleotide occupancies of t he alpha and beta subunits are unchanged except that both aluminium trifluo ride and Mg(2+)ADP are bound in the nucleotide-binding site of the PDP Subu nit. The presence of aluminium fluoride is accompanied by only minor adjust ments in the surrounding protein. Conclusions: The structure appears to mimic a possible transition state. Th e coordination of the aluminofluoride group has many features in common wit h other aluminofluoride-NTP hydrolase complexes. Apparently, once nucleotid e is bound to the catalytic beta subunit, no additional major structural ch anges are required for catalysis to occur.