Structural requirements of mastoparan for activation of membrane-bound guanylate cyclase

Mastoparan activated membrane-bound guanylate cyclase and potentiated the effect of atrial natriuretic factor (ANF) and ATP on guanylate cyclase activity in rat lung membranes. Mastoparan is a cationic, amphiphilic tetradecapeptide with an amidated carboxyl terminus. It takes the alpha-helical conformation upon interacting with the membrane. Several analogs were synthesized to study the role of the positive charges, the carboxyl amino group and the alpha-helical conformation of mastoparan in the activation of guanylate cyclase. The results showed that substitution of the C-terminal amide group of mastoparan with a carboxyl group significantly reduced its potency on the activation of guanylate cyclase. Replacement of three lysine residues of mastoparan with aspartic acid or serine residues completely abolished the stimulatory effect of mastoparan. When the alanine at position 10 of mastoparan was substituted by a proline, the resulting analog had no effect on guanylate cyclase activity. These results demonstrate that the positive charges and the helical structure of mastoparan are critical determinants for the activation of guanylate cyclase.