Cross-reconstitution studies with polypeptides of Escherichia coli and bovine heart mitochondrial F0F1 ATP synthase

The ATP synthase--a splendid molecular machine

An X-ray structure of the F1 portion of the mitochondrial ATP synthase shows asymmetry and differences in nucleotide binding of the catalytic beta subunits that support the binding change mechanism with an internal rotation of the gamma subunit. Other structural and mutational probes of the F1 and F0 portions of the ATP synthase are reviewed, together with kinetic and other evaluations of catalytic site occupancy and behavior during hydrolysis or synthesis of ATP. Subunit function as related to proton translocation and rotational catalysis is considered. Physical demonstrations of the gamma subunit rotation have been achieved. The findings have implications for other enzymatic catalyses.

The effect of mild trypsin digestion of F1 on energy coupling in the mitochondrial ATP synthase

Mild trypsin digestion of isolated bovine-heart mitochondrial F1-ATPase removed the first 15 residues from the N-terminus of subunit alpha under conditions in which other F1 subunits were apparently untouched. When the trypsinized F1 (TF1) was reconstituted with the F0 sector in the mitochondrial membrane (USMP), the ATP hydrolase activity acquired oligomycin sensitivity but ATP hydrolysis was decoupled from proton pumping. TF1 added to USMP did not block the proton channel in F0 as the native F1 did. AMP-PNP inhibited proton conductivity in reconstituted F1-USMP but this effect was lost in reconstituted TF1-USMP. These results indicate that the N-terminus of the F1 alpha subunit plays a critical role in the conformational communication between F1 and F0.

DCCD-sensitive proton permeability of bacterial photosynthetic membranes. Cross-reconstitution studies with purified bovine heart Fo subunits

The DCCD-sensitive proton permeability of chromatophores, from a green strain of Rhodobacter Capsulatus is potentiometrically detected following the proton release induced by a transmembrane diffusion potential imposed by a valinomycin-mediated potassium influx with a procedure already used for bovine heart submitochondrial particles (ESMP) and vesicles from Escherichia coli (Zanotti et al. (1994) Eur. J. Biochem. 222, 733-741). In the photosynthetic system, addition of increasing amounts of DCCD inhibits, with a similar titre, both proton permeability and MgATP-dependent ATPase activity as detected in the dark. The titre for 50% inhibition coincides with that obtained measuring proton permeability and ATP hydrolysis in ESMP. Upon removal of F1, the passive proton permeability is much less sensitive to DCCD in chromatophores than in USMP, suggesting that in chromatophores the F1-Fo interaction shapes the DCCD-sensitive proton conducting pathway. Addition of the purified mitochondrial FoI-PVP and oligomycin sensitivity-conferring (OSCP) proteins to the F1 stripped chromatophores restored the sensitivity of proton permeability to DCCD detected in untreated chromatophores. Analysis of the binding of 14C[DCCD] on F1 stripped chromatophores shows that the increase of DCCD sensitivity of proton permeability, caused by addition of mitochondrial Fo proteins, is related to an increase of the binding of the inhibitor to subunit c of Fo sector of ATP synthase complex.