PURIFICATION AND SEQUENCE DETERMINATION OF A NEW NEUTRAL MAMMALIAN NEUROTOXIN FROM THE SCORPION BUTHUS-MARTENSII KARSCH

A new neutral mammalian neurotoxin, designated BmK M4, with an isoelec tric point (pi) of 7.6 and a relatively low toxicity (LD50 = 4.0 +/- 0 .25 mu g/g mice, i.v.) was purified from the venom of scorpion Buthus martensii Karsch (BmK). The complete amino acid sequence of the toxin composed of 64 amino acid residues was determined by automated Edman d egradation of the N-terminal part of the reduced and S-carboxamidometh ylated protein (up to 30 amino acid residues) and its peptide fragment s degraded by lysylendopeptidase or Staphylococcus aureus V-8 protease . The calculated mel, wt based on the amino acid composition was 7001. By comparison with the sequences of other basic BmK mammalian neuroto xins, it was concluded that the weaker toxicity and lower pr value of BmK M4 might be the result of mutations H10E, R18G and K28D. The seque nce comparison of BmK M4 with an acidic toxin, BmK M8, showed that the weakest toxicity and acidic property of BmK M8 may be the consequence of mutations K8D, D53A, V55E and V59E. The substitution of 21 Gly in BmK M4 for Tyr in other BmK toxins may also be of importance. In their tertiary structures, these mutated charged residues are mainly distri buted in the surface (face B) that is roughly opposite to the ''conser ved hydrophobic surface'' (face A) proposed by Fontecilla-Camps et al. in 1982. Therefore the toxin-receptor interaction may take a multipos ition mode. Copyright (C) 1997 Elsevier Science Ltd.