Synthesis of the Mast Cell Degranulating (MCD) Peptide from Bee Venom

Further studies on the structural requirements for mast cell degranulating (MCD) peptide-mediated histamine release

Mast cell degranulating (MCD) peptide was modified in its two disulfide bridges and in the two arginine residues in order to measure the ability of these analogs to induce histamine release from mast cells in vitro. Analogs prepared were [Ala(3,15)]MCD, [Ala(5,19)]MCD, [Orn(16)]MCD, and [Orn(7,16)]MCD. Their histamine-releasing activity was determined spectrofluorometrically with peritoneal mast cells. The monocyclic analogs in which the cysteine residues were replaced pairwise with alanine residues showed three-to ten-fold diminished histamine-releasing activity respectively, compared with the parent MCD peptide. Substantial increases in activity were observed where arginine residues were replaced by ornithines. The ornithine-mono substituted analog showed an almost six-fold increase and the ornithine-doubly substituted analog three-fold increase in histamine-releasing activity compared with the parent MCD peptide. The structural changes associated with these activities were followed by circular dichroism (CD) spectroscopy. Changes in the shape and ellipticity of the CD spectra reflected a role for the disulfide bonds and the two arginine residues in the overall conformation and biological activity of the molecule.

Solid phase synthesis and biological activity of mast cell degranulating (MCD) peptide: a component of bee venom

Mast cell degranulating (MCD) peptide, a 22 amino acid residue basic peptide from bee venom, was synthesized by stepwise solid phase synthesis on a benzhydrylamine resin support. N alpha-t-butyloxycarbonyl and benzyl type side chain protection was used. The two disulfide bridges were formed selectively by using S-acetamidomethyl protection for the cysteine residues in position 5 and 19 and S-methylbenzyl protection for the cysteine residues in positions 3 and 15. Crude synthetic MCD peptide was obtained following deprotection and cleavage from the resin by the low/high HF method. The peptide was isolated in pure form by ion exchange chromatography and gel filtration. The final product has physical, chemical, and biological properties identical with those reported for the natural product. The synthetic strategy utilized for MCD peptide will facilitate the availability of structurally similar analogs for evaluating antihistaminic and anti-inflammatory activities.