Molecular basis of the mammalian potency of the scorpion α-like toxin, BmK M1

SPECIFIC AIMSIn this study, an effective yeast expression system was used to study the role of 14 N- and C-terminal residues from the α-like toxin BmK M1 from the Chinese scorpion Buthus martensii Karsch. Using site-directed mutagenesis, all of these residues were individually substituted by one or more amino acids, resulting in a total of 19 mutants. These were then subjected to a bioassay on mice, an elaborate electrophysiological characterization on three cloned voltage-gated Na+ channels (Nav1.2, Nav1.5, and para), and a circular dichroism analysis. Our results reveal large mutant-dependent differences that emphasize important and specific roles for the studied residues. By mutating single amino acids we were able to redirect the α-like characteristics of BmK M1 (active on mammals and insects) to much higher mammal specificity or, in a few cases, total insect specificity. This study therefore represents a thorough mapping and elucidation of three epitopes that underlie the molecular basis of the mamma...