Lysophospholipid headgroup size, and acyl chain length and saturation differentially affect vacuole acidification, Ca transport, and fusion.

SNARE-mediated membrane fusion is regulated by the lipid composition of the engaged bilayers. Lipid composition impacts fusion through direct protein lipid interactions or through modulating the physical properties of membranes at the site of contact, including the induction of positive curvature by lysophospholipids (LPLs). The degree of positive curvature induced is due to the length and saturation of the single acyl chain in addition to the size of the head group. Here we examined how yeast vacuole fusion and ion transport were differentially affected by changes in lysolipid properties. We found that lysophosphatidylcholine (LPC) with acyl chains containing 14-18 carbons all inhibited fusion with IC values ranging from ∼40-120 µM. The monounsaturation of LPC-18:1 had no effect when compared to its saturated counterpart LPC-18:0. On the other hand, head group size played a more significant role in blocking fusion as lysophosphatidic acid (LPA)-18:1 failed to fully inhibit fusion. We also show that both Ca uptake and SNARE-dependent Ca efflux was sensitive to changes in the acyl chain length and saturation of LPCs, while LPA only affected Ca efflux. Finally, we tested these LPLs on vacuole acidification by the V-ATPase. This showed that LPC-18:0 could fully inhibit acidification whereas other LPCs had moderate effects. Again, LPA had no effect. Together these data suggest that the effects of LPLs were due to a combination of head group size and acyl chain length leading to a range in degree of positive curvature.