Fluid Mechanical Matching of H+-ATPsynthase Subunit c Ring with Lipid Membranes Revealed by 2H Solid-State NMR.

Osaka University.

The F1Fo-ATP synthase utilizes the transmembrane H(+) gradient for the synthesis of ATP. Fo subunit c-ring plays a key role in transporting H(+) through Fo in the membrane. We investigated the interactions of E. coli subunit c with dimyristoyl phosphatidylcholine (DMPC-d54) at lipid/protein ratios of 50:1 and 20:1 by means of (2)H solid-state NMR. In the liquid-crystalline state of DMPC, the (2)H NMR moment values and the order parameter (SCD) profile were little affected by the presence of subunit c, suggesting that the bilayer thickness in the liquid-crystalline state is matched to the transmembrane hydrophobic surface of subunit c. On the other hand, hydrophobic mismatch of subunit c with the lipid bilayer was observed in the gel state of DMPC. Moreover, the viscoelastisity represented by a square-law function of the (2)H NMR relaxation was also little influenced by subunit c in the fluid phase, in contrast with flexible nonionic detergents or rigid additives. Thus, the hydrophobic matching of the lipid bilayer to subunit c involves at least two factors, the hydrophobic length and the fluid mechanical property. These findings may be important for the torque generation in the rotary catalytic mechanism of the F1Fo-ATPse molecular motor.

PMID: 18310246 [PubMed - as supplied by publisher]