The effects of acyl chain length and saturation of diacylglycerols and phosphatidylcholines on membrane monolayer curvature.

The second messenger, diacylglycerol (DAG), introduces negative curvature in phospholipid monolayers and strongly induces the lamellar (L(alpha)) to reverse hexagonal (H(II)) phase transition. The chain lengths and degree of unsaturation of symmetric DAGs influence this effect. Within dioleoylphosphatidylcholine (DOPC) monolayers, the apparent spontaneous radius of curvature (R(0)) of the short, saturated dicaprylglycerol (C10-DCG) itself was determined to be -13.3 A, compared with an R(0) value of -10.1 A for the long, di-monounsaturated dioleoylglycerol (C18-DOG). Such increased length and unsaturation of the DAG acyl chains produces this small change. Di-saturated phosphatidylcholines (PCs) with equal length chains (from C10-C18) with 25 mol % DOG do not form the H(II) phase, even under the unstressed conditions of excess water and alkane. Di-unsaturated PCs with equal chain length (from C14-C18) with 25 mol % DOG do form the H(II) phase. Asymmetric chained PCs (position 1 saturated with varying lengths, position 2 differentially unsaturated with varying lengths) all form the H(II) phase in the presence of 25 mol % DOG. As a general rule for PCs, their unsaturation is critical for the induction of the H(II) phase by DOG. The degree of curvature stress induced by the second messenger DOG in membranes, and any protein that might be affected by it, would appear to depend on chain unsaturation of neighboring PCs.