Spin label studies on the selectivity of lipid-protein interaction of cardiolipin analogues with the Na 2+/K 2+-ATPase

Abstract

The selectivity of lipid-protein interaction for various spin-labelled cardiolipin analogoues in Na +/K +- ATPase membranes from Squalus acanthias has been investigated by ESR spectroscopy. Cardiolipin derivatives with different numbers of acyl chains, or in which the headgroup charge has been removed by methylation of the phosphate groups, all show a pronounced selectivity relative to phosphatidylcholine. Maximally three times more of the cardiolipin analogue is associated with the protein, than is phosphatidylcholine. The selectivity pattern in the absence of salt is in the order: cardiolipin ≈ monolysocardiolipin ≥ acylcardiolipin > dimethylcardiolipin ⪢ phosphatidylcholine, where acylcardiolipin has the spin label chain attached to the centre-OH group of the headgroup. The degree of association of the negatively charged cardiolipinds with the protein is reduced by salt, corresponding to the lower selectivity for dimethylcardiolipin. It is concluded that the selectivity of the Na +/K +-ATPase for cardiolipin is not solely of electrostatic origin, nor is it likely the originate in the larger number of fatty acid chains relative to diacyl phospholipids.