Calmodulin-binding Peptides Isolated from Alpha-casein Peptone

Peptides that inhibit calmodulin-dependent cyclic nucleotide phosphodiesterase were isolated from a pepsin digest of alpha-casein. Analysis of these peptides showed that they corresponded to the alpha S2-casein sequences 164-179 (Leu-Lys-Lys-Ile-Ser-Gln-Arg-Tyr-Gln-Lys-Phe-Ala-Leu-Pro-Gln-Tyr). 183-206 (Val-Tyr-Gln-His-Gln-Lys-Ala-Met-Lys-Pro-Trp-Ile-Gln-Pro-Lys-Thr-Lys-Val -Ile- Pro-Tyr-Val-Arg-Tyr) and 183-207 (C-terminus, Val-Tyr-Gln-His-Gln-Lys-Ala-Met-Lys-Pro-Trp-Ile- Gln-Pro-Lys-Thr-Lys-Val-Ile-Pro-Tyr-Val-Arg-Tyr-Leu). These peptides inhibited calmodulin-induced cyclic nucleotide phosphodiesterase activity over the range 1-50 microM without affecting the basal enzyme activity. These results demonstrated that the affinities of these peptides for calmodulin are comparable to the affinities of certain endogenous neurohormones and proteins that interact with calmodulin.