Membrane anchoring of diacylglycerol lactones substituted with rigid hydrophobic acyl domains correlates with biological activities.

Summary Synthetic diacylglycerol lactones (DAG-lactones) are effective modulators of critical cellular signaling pathways, downstream of the lipophilic second messenger diacylglycerol, that activate a host of protein kinase C (PKC) isozymes as well as other non-kinase proteins that share with PKC similar C1 membrane-targeting domains. A fundamental determinant of the biological activity of these amphiphilic molecules is the nature of their interactions with cellular membranes. This study characterizes the membrane interactions and bilayer anchoring of a series of DAG-lactones in which the hydrophobic moiety is a “molecular rod”, namely a rigid 4-[2-(Rphenyl)ethynyl]benzoate moiety in the acyl position. Application of assays employing chromatic biomimetic vesicles and biophysical techniques reveals that the mode of membrane anchoring of the DAG-lactone derivatives was markedly affected by the presence of the hydrophobic diphenyl rod and by the size of the functional unit displayed at the terminus of the rod. Two primary mechanisms of interaction were observed: surface binding of the DAG-lactones at the lipid/water interface and deep insertion of the ligands into the alkyl core of the lipid bilayer. These membrane-insertion properties could explain the different patterns of PKC translocation from cytosol to membranes induced by the molecular-rod DAG-lactones. This investigation emphasizes that the side-residues of DAG-lactones, rather than simply conferring hydrophobicity, profoundly influence membrane interactions and in that fashion may further contribute to the diversity of biological actions of these synthetic biomimetic ligands.