All rotary ATPases catalyze the interconversion of ATP and ADP-Pi through a mechanism that is coupled to the transmembrane flow of H+ or Na+. Physiologically, however, F/A-type enzymes specialize in ATP synthesis driven by downhill ion diffusion, while eukaryotic V-type ATPases function as ion pumps. To begin to rationalize the molecular basis for this functional differentiation, we solved the crystal structure of the Na+-driven membrane rotor of the Acetobacterium woodii ATP synthase, at 2.1 Å resolution. Unlike known structures, this rotor ring is a 9:1 heteromer of F- and V-type c-subunits, and therefore features a hybrid configuration of ion-binding sites along its circumference. Molecular and kinetic simulations are used to dissect the mechanisms of Na+ recognition and rotation of this c-ring, and to explain the functional implications of the V-type c-subunit. These structural and mechanistic insights indicate an evolutionary path between synthases and pumps involving adaptations in the rotor ring.
The Na(+) F(1)F(O) ATP synthase of the anaerobic, acetogenic bacterium Acetobacterium woodii has a unique F(O)V(O) hybrid rotor that contains nine copies of a F(O)-like c subunit and one copy of a V(O)-like c(1) subunit with one ion binding site in four transmembrane helices whose cellular function is obscure. Since a genetic system to address the role of different c subunits is not available for this bacterium, we aimed at a heterologous expression system. Therefore, we cloned and expressed its Na(+) F(1)F(O) ATP synthase operon in Escherichia coli. A Δatp mutant of E. coli produced a functional, membrane-bound Na(+) F(1)F(O) ATP synthase that was purified in a single step after inserting a His(6)-tag to its β subunit. The purified enzyme was competent in Na(+) transport and contained the F(O)V(O) hybrid rotor in the same stoichiometry as in A. woodii. Deletion of the atpI gene from the A. woodii operon resulted in a loss of the c ring and a mis-assembled Na(+) F(1)F(O) ATP synthase. AtpI from E. coli could not substitute AtpI from A. woodii. These data demonstrate for the first time a functional production of a F(O)V(O) hybrid rotor in E. coli and revealed that the native AtpI is required for assembly of the hybrid rotor.
50 ml of a 10% fish oil emulsion (41% ω-3 fatty acids of total fatty acids) were infused for 1 h into the arm vein of young, healthy, male volunteers. The fatty acid composition of the plasma, aggregation of the blood platelets as well as the thromboxane synthesis, were measured before the beginning of infusion, 20, 60, 120, 360 and 1,440 min after the start of the fat infusion. In the first 60 min, the fatty acid composition of the plasma changed in correspondence with the supplied fatty acid pattern. At the end of the investigation it was again within the normal range. As a result of fat application thromboxane synthesis was reduced and the aggregation of the platelets was inhibited but it was normalized by the 1,440-min value. Fish oil emulsions might be beneficial for parenterally fed patients with a high risk of thrombosis. Therefore the performance of further investigations using a varying dosage and multiple application can be recommended.
Background:The peripheral stator stalk of Escherichia coli ATP synthase contains two b subunits. Results: Using disulfide bond formation, one b subunit was cross-linked to a, ␣, and ␦ and the other to .
Conclusion:The b subunits adopt distinct positions within the stator to generate stability. Significance: The different positions imply different roles in counteracting the torque generated by the rotor.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.