Binding of a synthetic beta-endorphin peptide to calmodulin

The 31-residue neuropeptide, beta-endorphin, inhibits the calmodulin-dependent activity of activatable cyclic nucleotide phosphodiesterase. We have shown that the amino terminal portion of the peptide, which includes the sequence conferring opiate activity, is not required for inhibitory potency and, furthermore, that solution complexes of the peptides and calmodulin render calmodulin functionally inactive in terms of cyclic nucleotide phosphodiesterase activation. An amino terminal deletion peptide of human beta-endorphin (beta-endorphin 13-31), synthesized using solid phase methods, was shown to interact with calmodulin by cross-linking with bis(sulfosuccinimidyl)suberate and by a gel permeation chromatographic technique. Results from the latter approach, using peptide concentrations of 2-100 microM, demonstrated Ca2+-dependent equilibrium binding with an apparent stoichiometry of approximately 4 mol of peptide/mol of calmodulin and half-maximal binding at 15-20 microM.