CHARACTERIZATION OF NOVEL CALMODULIN-BINDING PEPTIDES WITH DISTINCT INHIBITORY EFFECTS ON CALMODULIN-DEPENDENT ENZYMES

We describe the isolation and interaction with calmodulin (CaM) of two 10-amino-acid peptides (termed peptides 1 and 2; AWDTVRISFG and AWPSL QAIRG respectively) derived from a phage random peptide display librar y. Both peptides are shorter than previously described CaM-binding pep tides and lack certain features found in the sequences of CaM-binding domains present in CaM-activated enzymes. However, H-1 NMR spectroscop y and fluorimetry indicate that both peptides interact with CaM in the presence of Ca2+. The two peptides differentially inhibited CaM-depen dent kinases I and II (CaM kinases I and II) but did not affect CaM-de pendent phosphodiesterase, Peptide 1 inhibited CaM kinase I but not Ca M kinase II, whereas peptide 2 inhibited CaM kinase II, but only parti ally inhibited CaM kinase I at a more than 10-fold higher concentratio n. Peptide 1 also inhibited a plant calcium-dependent protein kinase, whereas peptide 2 did not. The ability of peptides 1 and 2 to differen tially inhibit CaM-dependent kinases and CaM-dependent phosphodiestera se suggests that they may bind to distinct regions of CaM that are spe cifically responsible for activation of different CaM-dependent enzyme s.