On the structure of the stator of the mitochondrial ATP synthase

The structure of most of the peripheral stalk, or stator, of the F-ATPase from bovine mitochondria, determined at 2.8 angstrom resolution, contains residues 79-183, 3-123 and 5-70 of subunits b, d and F-6, respectively. It consists of a continuous curved alpha-helix about 160 angstrom long in the single b-subunit, augmented by the predominantly alpha- helical d- and F-6-subunits. The structure occupies most of the peripheral stalk in a low-resolution structure of the F-ATPase. The long helix in subunit b extends from near to the top of the F-1 domain to the surface of the membrane domain, and it probably continues unbroken across the membrane. Its uppermost region interacts with the oligomycin sensitivity conferral protein, bound to the N-terminal region of one a- subunit in the F-1 domain. Various features suggest that the peripheral stalk is probably rigid rather than resembling a flexible rope. It remains unclear whether the transient storage of energy required by the rotary mechanism takes place in the central stalk or in the peripheral stalk or in both domains.