Injection of crude venom from the scorpion Orthochirus scrobiculosus into larvae of Heliothis virescens (Lepidoptera: Noctuidae) caused trembling and uncoordinated movement before development of a progressive and prolonged flaccid paralysis. The isolation of the toxin (OsI-1) responsible for this effect of O. scrobiculosus venom is described. The molecular mass of OsI-1 toxin was 6994 Da, as determined by desorption mass spectroscopy. The complete primary structure of OsI-1 was deduced from the sequence of cDNA clones obtained by rapid amplification of cDNA ends (RACE) PCR. Comparison of the deduced amino acid sequence of OsI-1 with those of other insecticidal scorpion toxins indicates that it is a sodium (Na+) channel active depressant insect-selective toxin. The analysis of amino acid sequence of the toxin in conjunction with mass spectroscopy data indicates post-translational modification in maturation with the removal of 3 C-terminal amino acids and amidation of the C-terminus. Copyright (C) 1999 Elsevier Science Ltd.
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