Structural and functional features of the Escherichia coli F₁-ATPase

The structural organization and overall dimensions of the Escherichia coli F₁-ATPase in solution has been analyzed by synchroton X-ray scattering. Using an independent ab initio approach, the low-resolution shape of the hydrated enzyme was determined at 3.2 nm resolution. The shape permitted unequivocal identification of the volume occupied by the α₃β₃γ complex of the atomic model of the ECF₁-ATPase. The position of the δ and ε subunits were found by interactive fitting of the solution scattering data and by cross-linking studies. Laser-induced covalent incorporation of 2-azido-ATP established a direct relationship between nucleotide binding affinity and the different interactions between the stalk subunits γ and ε with the three catalytic subunits (β) of the F₁-ATPase. Mutants of the ECF₁-ATPase with the introduction of Trp-for-Tyr replacement in the catalytic site of the complex made it possible to monitor the activated state for ATP synthesis (ATP conformation) in which the γ and ε subunits are in close proximity to the α subunits and the ADP conformation, with the stalk subunits are linked to the β subunit.