THE ROLE OF THE STALK IN THE COUPLING MECHANISM OF F1F0-ATPASES

The extrinsic and intrinsic membrane sectors of F1F0-ATPases are linked by a slender stalk 40-50 Angstrom in length. The stalk transmits the energy produced by oxidative or photosynthetic phosphorylation from the intrinsic sector, F-0, to the catalytic sites in the extrinsic F-1 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 delta and epsilon, part of the gamma-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 gamma, delta, epsilon, OSCP, F-6, b and d subunits all contribute to it. A bovine stalk complex has been assembled in vitro from bacterially expressed OSCP, F-6, b and d, both in the presence and in the absence of F-1-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 F-1 stalk complex may permit the high resolution structure of bovine F-1-ATPase to be extended into the stalk domain. Abstract