Makatoxin I, a Novel Toxin Isolated from the Venom of the Scorpion Buthus martensi Karsch, Exhibits Nitrergic Actions

Abstract

Buthus martensi Karsch venom exhibits nitrergic action in rat anococcygeus muscle (ACM). We have purified a novel toxin, makatoxin I (MkTx I), which exhibits nitrergic action, to homogeneity from this venom by a combination of gel-filtration, cation-exchange chromatography, and reverse-phase chromatography. Its purity was assessed by capillary electrophoresis and mass spectrometry. Its molecular weight was found to be 7031.71 ؎ 2.88 as calculated from electrospray mass spectrographic data. The complete amino acid sequence was elucidated by sequencing of reduced and S-pyridylethylated toxin and a carboxyl-terminal peptide, P55-64, generated by the cleavage of toxin with endoproteinase Lys-C. The complete sequence of MkTx I is GRDAYIADSENCTYTCALNPYCNDLCTKNGAKSGYCQ-WAGRYGNACWCIDLPDKVPIRISGSCR. This toxin is composed of 64 amino acid residues and contains 8 halfcystine residues. Structurally, MkTx I has high similarity to Bot I and Bot II when compared with toxins from other scorpion species. The effects of MkTx I on nitrergic responses were investigated using the rat isolated ACM mounted in Krebs solution (37°C, 5% CO 2 in O 2 ). MkTx I (2 g/ml) markedly relaxed the carbacholprecontracted ACM; the relaxation was inhibited by the stereoselective inhibitor of nitric oxide synthase, Nnitro-L-arginine methyl ester (50 M). Thus, MkTx I is the first ␣-toxin that can mediate nitrergic responses in the rat isolated ACM.Scorpion venoms consist of complex mixtures of several toxins that exhibit various pharmacological activities including selective actions at sodium and potassium channels, which are the major molecular targets of scorpion toxins (1). The scorpion Buthus martensi Karsch is widely distributed in China (2), but relatively few reports have been published on the biological properties of its venom (MKV) 1 or toxins. Electrophysiological studies indicate that MKV contains some neurotoxic compounds that possibly act on the Na 1ϩ channels in the excitable membrane of nerve and muscle (3), cultured mouse cardiomyocyte (4), and rat anterior pituitary cells (5).In a preliminary study we observed that MKV produced relaxant responses of the rat precontracted anococcygeus muscle (ACM), suggesting that some constituent toxin(s) present in MKV could mimic the effects of nitrergic transmission involving the release of the inhibitory neurotransmitter nitric oxide (NO).2 Therefore, we were interested in isolating and purifying the bioactive component(s) present in the venom as well as identifying and characterizing the pure toxin(s) mediating the relaxant responses of the rat ACM. In this communication we report the isolation, purification, and complete amino acid sequence of a novel toxin, MkTx I, isolated from the venom of B. martensi Karsch and provide the first documentation of some novel nitrergic actions mediated by a scorpion toxin. MATERIALS AND METHODSDrugs and Chemicals-The bright white lyophilized crystals of crude venom of B. martensi Karsch were obtained from the Huazhen Pharmaceutical Animal Research Institute (Gu...

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Evolutionary Diversification of Mesobuthus α-Scorpion Toxins Affecting Sodium Channels

“…Clade I includes most of M. eupeus toxins and several toxins from M. martensii, in which BmKM1, an ␣-like toxin with activity on both insect and mammalian VGSCs, can be considered as the prototype of this clade (32). Members in clade III have been found to evolve distinct functional feature that exhibits nitrergic actions (40). Clade 4 only includes two M. eupeus toxins (MeuNaTx␣-2 and -9) with the closest distance to Clade 5 that contains BmK␣IV, a functional hybrid of ␣-toxins (41).…”

Toxin Diversity Revealed by a Transcriptomic Study of Ornithoctonus huwena

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