INTERACTION OF SMOOTH-MUSCLE CALPONIN WITH PHOSPHOLIPIDS

Analyzing the primary structure we predicted that calponin may interact with phospholipids. In order to check this suggestion we investigated the interaction of calponin with phospholipids by ultracentrifugation, light scattering, vesicles leakage and differential scanning calorimetry. In agreement with our prediction calponin interacts with acidic phospholipids and the phospholipid-binding site was located in the short (13 kDa) N-terminal chymotryptic peptide of calponin, The apparent dissociation constant of calponin-phospholipids complex was less than 0.2 mu M and calmodulin competes with phospholipids for calponin binding, Although the interaction of calponin with phospholipids decreases at high ionic strength, calponin binds phospholipids even in the presence of 100-150 mM, of the salt, Under certain conditions calponin induced leakage of phospholipid vesicles and affected the cooperativity of lipid phase transition, It is concluded that both electrostatic and hydrophobic interactions provide for calponin-phospholipid complex formation.