SPHINGOLIPID-DERIVED SIGNALING MODULATORS - INTERACTION WITH PHOSPHATIDYLSERINE

We previously described the synthesis of two deuterium-labelled sphing oid bases, which made it possible to perform NMR spectroscopy on this family of signalling modulators in membranes (Rigby, A.C, Barber, K.R and Grant, C.W.M. (1995) Biochim. Biophys. Acta 1240, 75-82). In the p resent work we sought to test the concept that such mediators may disp lay altered physical behaviour through association with anionic lipids - as a possible mechanism of involvement in signal transduction. Lyso -dihydrogalactosylceramide with deuterium nuclei at C-4, and C-5 of th e sphingosine backbone and at C'(3) and C'(4) of the galactose ring ([ H-2(4)]lyso-GalCer), and N,N-dimethylsphingosine with deuterated amino -methyl groups ([H-2(3)]dimethylsphingosine), were assembled as minor components into unsonicated fluid bilayer membranes of palmitoyl-2-ole oylphosphatidylcholine/cholesterol. The effect of (anionic) phosphatid ylserine was considered in this zwitterionic host matrix. The results present a picture of rapidly reversible interaction. The (-) charged p hosphatidylserine exerted readily-measurable control over the orientat ion of the carbohydrate residue of [H-2(4)]lyso-GalCer. In contrast, s urrounding (-) charges exerted little spectral influence at the level of C-4 and C-5 of the lyso-GalCer, membrane-inserted, backbone; or at the level of the amino group of dimethylsphingosine. It would appear t hat packing alterations induced by the phosphatidylserine/sphingoid ba se association can translate into sizeable spatial constraints in the neighbouring aqueous domain.