Chemical synthesis and characterization of maurocalcine, a scorpion toxin that activates Ca2+ release channel/ryanodine receptors

Maurocalcine is a novel toxin isolated from the venom of the chactid scorpi on Scorpio maurus palmatus, It is a 33-mer basic peptide cross-linked by th ree disulfide bridges, which shares 82% sequence identity with imperatoxin A, a scorpion toxin from the venom of Pandinus imperator. Maurocalcine is p eculiar in terms of structural properties since it does not possess any con sensus motif reported so far in other scorpion toxins. Due to its low conce ntration in venom (0.5% of the proteins), maurocalcine was chemically synth esized by means of an optimized solid-phase method, and purified after fold ing/oxidation by using both C18 reversed-phase and ion exchange high-pressu re liquid chromatographies, The synthetic product (sMCa) was characterized. The half-cystine pairing pattern of sMCa was identified by enzyme-based cl eavage and Edman sequencing. The pairings were Cys3-Cys17, Cys10-Cys21, and Cys16-Cys32, In vivo, the sMCa was lethal to mice following intracerebrove ntricular inoculation (LD50, 20 mu g/mouse). In vitro, electrophysiological experiments based on recordings of single channels incorporated into plana r lipid bilayers showed that sMCa potently and reversibly modifies channel gating behavior of the type 1 ryanodine receptor by inducing prominent subc onductance behavior. (C) 2000 Federation of European Biochemical Societies.