Energy conversion in biological systems is underpinned by membrane-bound proton
transporters that generate and maintain a proton electrochemical gradient across the
membrane which used, e.g. for generation of ATP by the ATP synthase. Here, we have
co-reconstituted the proton pump cytochrome bo3 (ubiquinol
oxidase) together with ATP synthase in liposomes and studied the effect of changing
the lipid composition on the ATP synthesis activity driven by proton pumping. We
found that for 100 nm liposomes, containing 5 of each proteins, the ATP synthesis
rates decreased significantly with increasing fractions of DOPA, DOPE, DOPG or
cardiolipin added to liposomes made of DOPC; with e.g. 5% DOPG, we observed an
almost 50% decrease in the ATP synthesis rate. However, upon increasing the average
distance between the proton pumps and ATP synthases, the ATP synthesis rate dropped
and the lipid dependence of this activity vanished. The data indicate that protons
are transferred along the membrane, between cytochrome bo3 and the
ATP synthase, but only at sufficiently high protein densities. We also argue that
the local protein density may be modulated by lipid-dependent changes in
interactions between the two proteins complexes, which points to a mechanism by
which the cell may regulate the overall activity of the respiratory chain.