CHARACTERIZATION OF 4 TOXINS FROM BUTHUS-MARTENSI SCORPION-VENOM, WHICH ACT ON APAMIN-SENSITIVE CA2-ACTIVATED K+ CHANNELS()

Four peptidyl inhibitors of the small-conductance Ca2+-activated K+ ch annels (SKCa have been isolated from the venom of the Chinese scorpion Buthus martensi. These peptides were identified by screening C-18 HPL C fractions of the crude Venom by means of mass analysis by matrix-ass isted-laser-desorption/ionization time-of-flight mass spectrometry, an d toxicological tests in mice. Edman degradation analysis of the purif ied peptides showed sequences of 28-31 amino acids including 6 cystein e residues. Three of the sequences were similar to the P01 peptides fr om Androctonus scorpions, showing 76% sequence similarity for the most closely related, named BmP01, and 46% for the other two, named BmP02 and BmP03. Like the P01 peptides, these molecules showed a low toxic a ctivity in mice after intracerebroventricular injection, and competed (K-0.5 > 1 mu M) With iodinated apamin for binding to its receptor sit e from rat brain, which has been proved to be the SKCa, channels. The fourth toxin was structurally related to the P05/leiurotoxin I toxin f amily, with 90% similarity, and was named BmP05. This toxin exhibited a high toxic activity with lethal effects in mice. Due to its small re presentation in the venom [less than 0.01% (by mass)], its biological properties have been assessed on the synthetic analogue of BmP05, whic h was assembled on a solid phase by means of Fmoc methodology. The syn thetic peptide was physicochemically identical to the natural peptide, as shown by comparison of their molecular masses and amino acid compo sitions, and by their coelution after coinjection on capillary electro phoresis. These results confirmed the primary structure of BmP05 inclu ding an amidated C-terminus. Similarly to natural BmP05, synthetic BmP 05 produced toxic and lethal effects after intracerebroventricular inj ection in mice (LD50 = 37 ng), and was able to compete with iodinated apamin for binding to its receptor in rat brain (K-0.5 = 20 pM).