LEIUROTOXIN-I, A SCORPION TOXIN SPECIFIC FOR CA2-ACTIVATED K+ CHANNELS - STRUCTURE-ACTIVITY ANALYSIS USING SYNTHETIC ANALOGS()

Recently, we reported a structure-activity relationship study on P05, a novel leiurotoxin I-like scorpion toxin which is selective for the a pamin-sensitive Ca2+-activated K+ channel [Sabatier ct al. (1993) Bioc hemistry 32, 2763-2770]. Arg(6), Arg(7), and C-terminal His(31) appear ed to be key residues for P05 biological activity. Owing to the high s equence identity between P05 and leiurotoxin I (87%), several analogs of leiurotoxin I (Lei-NH2) with point mutations at these positions wer e designed and chemically synthesized using an optimized solid-phase t echnique. The synthesized peptides were [L(6)]Lei-NH2, [R(7)]Lei-NH2, Lei-OH and [R(7)]Lei-OH, as well as fragment [R(7),Abu(8)]N4-S11-NH2. A chimeric analog ([M(22),K-24,R(27)]Lei-NH2), which possesses part of the iberiotoxin C-terminus, was also constructed. Circular dichroism analyses of these analogs, in agreement with their structural models o btained by molecular dynamics, showed that the point mutations did not significantly affect the overall secondary structures, as compared to natural Lei-NH2. All the peptides and natural toxins were compared in vitro for their capacity to inhibit binding of [I-125]-apamin to rat brain synaptosomes, and in vivo for their specific neurotoxicity in mi ce. The Args residue was essential for high biological activity of lei urotoxin I. Further, substitution of Met(7) in the natural toxin by Ar g(7), or C-terminal amidation of His(31), greatly increased affinity f or the apamin receptor but did not significantly affect toxin neurotox icity. Remarkably, the chimeric analog [M(22),K-24,R(27)]Lei-NH2 was f ound to retain leiurotoxin I-like activity, thus indicating that the n egatively charged residues Asp(24) and Glu(27) (and Ile(22)) are not d irectly involved in the high toxin bioactivity. However, the chimeric molecule had no iberiotoxin-like effect on rat muscular maxi-K+ channe ls incorporated in lipid bilayers. (C) Munksgaard 1994.