On the structure of the stator of the mitochondrial ATP synthase

Abstract

The structure of most of the peripheral stalk, or stator, of the F-ATPase from bovine mitochondria, determined at 2.8 A resolution, contains residues 79-183, 3-123 and 5-70 of subunits b, d and F6, respectively. It consists of a continuous curved alpha-helix about 160 A long in the single b-subunit, augmented by the predominantly alpha-helical d- and F6-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 F1 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 alpha-subunit in the F1 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.

Figure 1

The structure of a subcomplex of the peripheral stalk of the F-ATPase from bovine mitochondria. The structure consists of residues 79–183 of subunit b, residues 3–123 of subunit d and residues 5–70 of F₆, shown in magenta, orange and green, respectively. Their N- and C-terminals are indicated.

Figure 2

The composite structure of the ATP synthase from mitochondria. Detailed structures of the F₁c₁₀ subcomplex (grey), the N-terminal domain of the OSCP (cyan) and the peripheral stalk subcomplex (magenta, orange and green) were introduced by eye into an electron density map determined by averaging single particles of the intact bovine complex observed by electron cryo-microscopy. (A) side view; (B) residual density corresponding to the peripheral stalk and the second domain of F_o (Rubinstein et al, 2003). Dotted lines represent the lipid bilayer; (C) view looking down onto the ‘crown' of the F₁ catalytic domain. The scale bar is 50 Å.

Figure 3

Locations of regions of the peripheral stalk subunits that were deleted in the subcomplex. Subunits b, d, F₆ and OSCP are shown in magenta, orange, green, and cyan, respectively. In (A), I, II and III indicate regions that probably accommodate residues 121–190, 185–214 and 125–160 of subunits OSCP, b and d, respectively. In (B), residues 188–214 of subunit b have been modelled as an α-helix shown in purple lying antiparallel to the central α-helix. Residues 125–160 of subunit d are modelled in yellow as an extended region from residues 125–131 followed by a short α-helix (residues 132–138) approximately orthogonal to the plane of the paper and an extended region parallel to the central α-helix in the b-subunit.