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Abstract

(1) Previous mutational analyses have shown that residue beta R398 of the beta-subunit is a key residue for binding of the inhibitory antibiotic aurovertin to Escherichia coli F₁F_o-ATP synthase. Here, we studied purified F₁ from the beta R398C and beta R398W mutants. ATPase activity in both cases was resistant to aurovertin inhibition. The fluorescence spectrum (lambda _exc = 278 or 295 nm) of beta R398W F₁ showed a significant red-shift as compared to wild-type and beta R398C enzymes, indicating that residue beta R398 lies in a polar environment. On the basis of this and previous evidence, we propose that aurovertin binding to F₁-ATPase involves a specific charged donor-acceptor H-bond between residue beta R398 and the 7-hydroxyl group of aurovertin. (2) The fluorescent substrate analog lin-benzo-ADP was shown to bind to beta R398W F₁ catalytic sites with the same K_d values as to wild-type F₁, and with the same quenching of the fluorescence of the analog. Fluorescence energy transfer was seen between the beta R398W residue and bound lin-benzo-ADP. Analysis of transfer efficiency at varying stoichiometry of bound lin-benzo-ADP showed that interaction occurred between one beta R398W residue and one catalytic-site-bound analog molecule at a distance of approximately 23 A. The relationships of the aurovertin and catalytic sites in the primary and tertiary structure are discussed.