Circular dichroic studies of protein kinase C and its interactions with calcium and lipid vesicles

Circular dichroism was used to study the secondary structure of protein kinase C (PKC) in aqueous solution and the conformational changes resulting due to the presence of its regulatory cofactors (e.g. Ca2+, phosphatidylserine (PS) and phorbol 12-myristate 13-acetate (PMA)). Computer analysis of the CD data for the estimates of secondary structure showed that PKC maintains a highly ordered structure containing 36% alpha-helix, 57% beta-sheet and 7% beta-turn. PKC displays a minor conformational change upon addition of Ca2+. However, a larger change is observed on adding phosphatidylserine vesicles in the presence of Ca2+. In this case, the alpha-helix content is decreased by approx. 35% and beta-sheet increased by approx. 16%. The protein does not experience further significant changes in conformation on adding PMA.