THE F₀F₁-TYPE ATP SYNTHASES OF BACTERIA: Structure and Function of the F₀ Complex

Abstract

Membrane-bound ATP synthases (F0F1-ATPases) of bacteria serve two important physiological functions. The enzyme catalyzes the synthesis of ATP from ADP and inorganic phosphate utilizing the energy of an electrochemical ion gradient. On the other hand, under conditions of low driving force, ATP synthases function as ATPases, thereby generating a transmembrane ion gradient at the expense of ATP hydrolysis. The enzyme complex consists of two structurally and functionally distinct parts: the membrane-integrated ion-translocating F0 complex and the peripheral F1 complex, which carries the catalytic sites for ATP synthesis and hydrolysis. The ATP synthase of Escherichia coli, which has been the most intensively studied one, is composed of eight different subunits, five of which belong to F1, subunits alpha, beta, gamma, delta, and epsilon (3:3:1:1:1), and three to F0, subunits a, b, and c (1:2:10 +/- 1). The similar overall structure and the high amino acid sequence homology indicate that the mechanism of ion translocation and catalysis and their mode of coupling is the same in all organisms.

Diversity of transport mechanisms: common structural principles

“…It is interesting to speculate that other primary transporters might have evolved from secondary transporters. Two examples of such systems are the F o F 1 H ϩ -translocating ATPases 26 and the ABC transporters 27 . The F o F 1 is composed of the F 1 catalytic sector, which is a soluble ATPase in the absence of the F o sector.…”

Membrane Topology of Subunit a of the F1F0 ATP Synthase as Determined by Labeling of Unique Cysteine Residues

“…[1][2][3][4]. It comprises an F 1 complex, which contains the nucleotide-binding subunits involved in catalysis, and an F 0 complex, which conducts protons across the membrane.…”

Turnover Number of Escherichia coli F0F1 ATP Synthase for ATP Synthesis in Membrane Vesicles

“…Energy released by proton translocation through F,, is relayed to the catalytic sites in F, by conformational changes. In Escherichia coli, the F, complex is composed of the three different polypeptides a, b, and c in a stoichiometry of 1 : 2: 10 t 1, whereas the F, complex consists of five subunits with a stoichiometry of a&& (Fillingame, 1990, 1992: Capaldi et al, 1994Deckers-Hebestreit and Altendorf, 1996). Recently, the F, part of bovine heart mitochondria was crystallized and the structures of the subunits a, / l , and part of 7 , have been solved by X-ray diffraction at 0.28-nm resolution (Abrahams et al, 1994).…”