des-(1-13) human beta-endorphin interacts with calmodulin

Binding of amphiphilic peptides to a carboxy-terminal tryptic fragment of calmodulin

Calmodulin (CaM) fragments 1-77 (CaM 1-77) and 78-148 (CaM 78-148) were prepared by tryptic cleavage of CaM. CaM 78-148 exhibited Ca2+-dependent binding to mastoparan X, Polistes mastoparan, and melittin with apparent dissociation constants less than 0.2 microM as judged from changes in the fluorescence spectrum and anisotropy of the single tryptophan residue of each of these cationic, amphiphilic peptides. This interaction was accompanied by a large spectral blue shift of the peptide fluorescence spectrum. These findings are consistent with earlier results [Malencik, D.A., & Anderson, S.R. (1984) Biochemistry 23, 2420-2428] on the binding of mastoparan X to CaM fragment 72-148. The binding of the peptide to CaM 78-148 also caused a significant loss of the accessibility of the peptide tryptophan to the fluorescence quencher acrylamide. The CaM 78-148 induced effects on the fluorescence spectra and tryptophan accessibility of the peptides were most pronounced for mastoparan X, a peptide with tryptophan on the apolar face of the putative amphiphilic helix. The data were comparable with results from parallel experiments on the Ca2+-dependent interaction of these peptides with intact CaM. Difference circular dichroic spectra suggested that binding to CaM 78-148 was associated with the induction of considerable degrees of helicity in the amphiphilic peptides, which by themselves have predominantly random coil structures in aqueous solution. This finding is also reminiscent of the interaction of these peptides with intact CaM.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of alpha-N-Acetyl-beta-endorphin and calmodulin

Acetylation at the alpha-amino terminal is a common post-translational modification of many peptides and proteins. In the case of the potent opiate peptide beta-endorphin, alpha-N-acetylation is a known physiological modification that abolishes opiate activity. Since there are no known receptors for alpha-N-acetyl-beta-endorphin, we have studied the association of this peptide with calmodulin, a calcium-dependent protein that binds a variety of peptides, phenothiazines, and enzymes, as a model system for studying acetylated endorphin-protein interactions. Association of the acetylated peptide with calmodulin was demonstrated by cross-linking with bis(sulfosuccinimidyl)suberate; like beta-endorphin, adducts containing 1 mol and 2 mol of acetylated peptide per mole calmodulin were formed. Some of the bound peptides are evidently in relatively close proximity to each other since, in the presence of amidated (i.e., lysine-blocked) calmodulin, cross-linking yielded peptide dimers. The acetylated peptide exhibited no appreciable helicity in aqueous solution, but in trifluoroethanol (TFE) considerable helicity was formed. Also, a mixture of acetylated peptide and calmodulin was characterized by a circular dichroic spectrum indicative of induced helicity. Empirical prediction rules, applied earlier to beta-endorphin, suggest that residues 14-24 exhibit alpha-helix potential. This segment has the potential of forming an amphipathic helix; this structural unit is believed to be important in calmodulin binding. The acetylated peptide was capable of inhibiting the calmodulin-mediated stimulation of cyclic nucleotide phosphodiesterase (EC 3.1.4.17) activity with an effective dose for 50% inhibition of about 3 microM; this inhibitory effect was demonstrated using both an enzyme-enriched preparation as well as highly purified enzyme. Thus, acetylation at the alpha-amino terminal of beta-endorphin, although abolishing opiate activity, does not interfere with the binding to calmodulin. Indeed, beta-endorphin and the alpha-N-acetylated peptide behave very similarly with respect to calmodulin association.

Inhibition of calmodulin-stimulated phosphodiesterase activity by vasoactive intestinal peptide

The effects of certain peptides of the glucagon family on calmodulin activity were determined from their capacity to inhibit a calmodulin-dependent form of phosphodiesterase. Vasoactive intestinal peptide and secretin were potent inhibitors of calmodulin activity, having IC50 values of 0.5 microM and 2 microM, respectively. By contrast, glucagon failed to inhibit calmodulin activity even at concentrations of 100 microM. None of these compounds significantly inhibited the basal activity of phosphodiesterase at concentrations up to 100 microM. These findings support the suggestion that important structural features of peptides for anticalmodulin activity include a net positive charge and a hydrophobic surface.

The functional nature of calcium binding units in calmodulin, troponin C and parvalbumin

Examination of the interaction of major tranquilizers with calmodulin results in the generalization that the functional nature of calcium binding helix-loop-helix regions found in several calcium binding proteins including calmodulin, troponin C and parvalbumin is dependent upon the topography of the hydrophobic and hydrophilic regions on the amphiphilic N-terminal alpha-helix of the helix-loop-helix conformation formed by the binding of the calcium cation to these proteins. The relation of the topography of this amphiphilic alpha-helix to drug binding is delineated at the molecular level and the results obtained are used to describe the interaction of beta-endorphin, dynorphin, alpha-MSH and other peptides with calmodulin. The utility of this hypothesis is further demonstrated by the description of a possible interaction between troponin C, troponin I and troponin T of the troponin complex in skeletal muscle.