A mechanism for the partial insertion of protein kinase C into membranes

We propose that the principle driving force allowing protein kinase C (PKC) to insert partway into membranes is the transient creation of an interior hydrophilic phase within the membrane. We further suggest that this phase i s composed of non-bilayer-forming elements, such as diacylglycerol or phorb ol eaters. We used the combination of fluorescence resonance energy transfe r (using fluorescently labeled phospholipid molecules and the endogenous tr yptophan residues of PMC) and fluorescence quenching by the water-soluble r eagent potassium iodide. The experimental system used micelles and purified PKC. Our model accounts for both the established kinetic data on PKC as we ll as the physical requirements of protein-membrane interaction. Moreover, it establishes PHC as the first example of a partially embedded membrane pr otein, and provides a mechanism to account for its activation. (C) 2001 Aca demic Press.