The role of the stalk in the coupling mechanism of F1F0‐ATPases

Abstract

The extrinsic and intrinsic membrane sectors of F₁F₀-ATPases are linked by a slender stalk 40–50 Å in length. The stalk transmits the energy produced by oxidative or photosynthetic phosphorylation from the intrinsic sector, F₀, to the catalytic sites in the extrinsic F₁ sector. How this is achieved is unknown, but long-range conformational changes linked to transmembrane proton transport may be involved. In bacterial and chloroplast F₁F₀-ATPases, the stalk is probably a composite of subunits δ and ε, part of the γ-subunit, and the extrinsic membrane domains of 2 subunits (identical or non-identical according to the species) that are bound to the membrane by their N-terminal regions. The stalk in the bovine mitochondrial enzyme appears to be more complex, and the γ, δ, ε, OSCP, F₆, b and d subunits all contribute to it. A bovine stalk complex has been assembled in vitro from bacterially expressed OSCP, F₆, b and d, both in the presence and in the absence of F₁-ATPase. One molecule of each of these subunits is present in the assembled complexes, as there is also in each native F₁F₀-ATPase assembly. Providing that suitable crystals can be obtained, the stalk complex and the F₁·stalk complex may permit the high resolution structure of bovine F₁-ATPase to be extended into the stalk domain.