Specificity and mechanism of protein kinase C activation by sn-1,2-diacylglycerols

The specificity of protein kinase C activation by sn-1,2-diacylglycerols and analogues was investigated by using a Triton X-100 mixed micellar assay. Analogues containing acyl or alkyl chains 8 carbons in length were synthesized because sn-1,2-diacylglycerol is an effective cell-permeant activator of protein kinase C. These analogues were tested as activators and antagonists of rat brain protein kinase C to determine the exact structural features important for activity. The analogues established that activation of protein kinase C by diacylglycerols is highly specific. Several analogues established that both carbonyl moieties of the oxygen esters are required for maximal activity and that the 3-hydroxyl moiety is also required. None of the analogues were antagonists. These data, combined with previous investigations, permitted formulation of a model of protein kinase C activation. A 3-point attachment of sn-1,2-diacylglycerol to the surface-bound protein kinase C-phosphatidylserine-Ca²⁺ complex is envisioned to cause activation. Direct ligation of diacylglycerol to Ca²⁺ is proposed to be an essential step in the mechanism of activation of protein kinase C.