The N-termini of the alpha and beta subunits at the top of F1 stabilize the energy-transfer function in the mitochondrial F1Fo ATP synthase

Effect of the ATPase inhibitor protein IF1 on H+ translocation in the mitochondrial ATP synthase complex

The H(+) F(o)F(1)-ATP synthase complex of coupling membranes converts the proton-motive force into rotatory mechanical energy to drive ATP synthesis. The F(1) moiety of the complex protrudes at the inner side of the membrane, the F(o) sector spans the membrane reaching the outer side. The IF(1) component of the mitochondrial complex is a basic 10 kDa protein, which inhibits the F(o)F(1)-ATP hydrolase activity. The mitochondrial matrix pH is the critical factor for the inhibitory binding of the central segment of IF(1) (residue 42-58) to the F(1)-alpha/beta subunits. We have analyzed the effect of native purified IF(1) the IF(1)-(42-58) synthetic peptide and its mutants on proton conduction, driven by ATP hydrolysis or by [K(+)] gradients, in bovine heart inside-out submitochondrial particles and in liposome-reconstituted F(o)F(1) complex. The results show that IF(1), and in particular its central 42-58 segment, displays different inhibitory affinity for proton conduction from the F(1) to the F(o) side and in the opposite direction. Cross-linking of IF(1) to F(1)-alpha/beta subunits inhibits the ATP-driven H(+) translocation but enhances H(+) conduction in the reverse direction. These observation are discussed in terms of the rotary mechanism of the F(o)F(1) complex.

The structural and functional connection between the catalytic and proton translocating sectors of the mitochondrial F1F0-ATP synthase

The structural and functional connection between the peripheral catalytic F1 sector and the proton-translocating membrane sector F0 of the mitochondrial ATP synthase is reviewed. The observations examined show that the N-terminus of subunit gamma, the carboxy-terminal and central region of F0I-PVP(b), OSCP, and part of subunit d constitute a continuous structure, the lateral stalk, which connects the peripheries of F1 to F0 and surrounds the central element of the stalk, constituted by subunits gamma and delta. The ATPase inhibitor protein (IF1) binds at one side of the F1F0 connection. The carboxy-terminal segment of IF1 apparently binds to OSCP. The 42L-58K segment of IF1, which is per se the most active domain of the protein, binds at the surface of one of the three alpha/beta pairs of F1, thus preventing the cyclic interconversion of the catalytic sites required for ATP hydrolysis.

F1 and F0 connections in the bovine mitochondrial ATP synthase: the role of the of alpha subunit N-terminus, oligomycin-sensitivity conferring protein (OCSP) and subunit d

We have studied the functional effect of limited proteolysis by trypsin of the constituent subunits in the native and reconstituted F1F0 complex and isolated F1 of the bovine heart mitochondrial ATP synthase (EC 3.6.1.34). Chemical cross-linking of oligomycin-sensitivity conferring protein (OSCP) with other subunits of the ATP synthase and the consequent functional effects were also investigated. The results obtained show that the alpha subunit N-terminus is essential for the correct, functional connection of F1 to F0. The alpha-subunit N-terminus contacts OSCP which, in turn, contacts the F0I-PVP(b) and the F0-d subunits. The N-terminus of subunit alpha, OSCP, a segment of subunit d and the C-terminal and central region of F0I-PVP(b) subunits are peripherally located with respect to subunits gamma and delta which are completely shielded in the F1F0 complex against trypsin digestion. This qualifies the N-terminus of subunit alpha, OSCP, subunit d and F0I-PVP(b) as components of the lateral element of the stalk. These subunits, rather than being confined at one side of the complex which would leave most of the central part of the gamma subunit uncovered, surround the gamma and the delta subunits located in the central stalk.

Structure/function of the beta-barrel domain of F1-ATPase in the yeast Saccharomyces cerevisiae

The first 90 amino acids of the alpha- and beta-subunits of mitochondrial F1-ATPase are folded into beta-barrel domains and were postulated to be important for stabilizing the enzyme (Abrahams, J. P., Leslie, A. G., Lutter, R., and Walker, J. E. (1994) Nature 370, 621-628). The role of the domains was studied by making chimeric enzymes, replacing the domains from the yeast Saccharomyces cerevisiae enzyme with the corresponding domains from the enzyme of the thermophilic bacterium Bacillus PS3. The enzymes containing the chimeric alpha-, beta-, or alpha- and beta-subunits were not functional. However, gain-of-function mutations were obtained from the strain containing the enzyme with the chimeric PS3/yeast beta-subunit. The gain-of-function mutations were all in codons encoding the beta-barrel domain of the beta-subunit, and the residues appear to map out a region of subunit-subunit interactions. Gain-of-function mutations were also obtained that provided functional expression of the chimeric PS3/yeast alpha- and beta-subunits together. Biochemical analysis of this active chimeric enzyme indicated that it was not significantly more thermostable or labile than the wild type. The results of this study indicate that the beta-barrel domains form critical contacts (distinct from those between the alpha- and beta-subunits) that are important for the assembly of the ATP synthase.