Covalent structures of BmK AS and BmK AS-1, two novel bioactive polypeptides purified from Chinese scorpion Buthus martensi Karsch

Complete amino acid sequences of two novel bioactive polypeptides, each con taining 66 amino acid residues, BmK AS and BmK AS-1 purified from the venom of Chinese scorpion Buthus martensi Karsch, have been determined by Edman sequencing and mass spectrometry on native proteins, reduced and S-carboxym ethylated proteins and their peptides obtained after cleavage with proteoly tic enzymes. Sequence analysis showed 86.4% structural identity between BmK AS and BmK AS-1 and also a high sequence similarity between BmK ASs and Aa H IT4, a unique anti-insect toxin and a ligand of Na+ channels obtained fro m Sahara scorpion A. australis Hector, but poor sequence homology between B mK RSs and those of the known alpha-, beta-type and long-chain insect-selec tive type scorpion neurotoxins. The positions of four disulfide bridges in BmK AS-I were established as Cys-12 and Cys-62, Cys-16 and Cys-37, Cys-23 a nd Cys-44, and Cys-27 and Cys-46, which are the same as those in alpha- and beta-scorpion neurotoxins. These results suggest that BmK ASs and AaH IT4 may form a new group sharing similar structural and functional properties i n the family of scorpion neurotoxic polypeptides. (C) 1999 Elsevier Science Ltd. All rights reserved.