Miniaturization of scorpion beta-toxins uncovers a putative ancestral surface of interaction with voltage-gated sodium channels.
The bioactive surface of scorpion beta-toxins that interact with receptor site-4 at voltage-gated sodium channels is constituted of residues of the conserved betaalphabetabeta core and the C-tail. In an attempt to evaluate the extent by which residues of the toxin core contribute to bioactivity, the anti-insect and anti-mammalian beta-toxins Bj-xtrIT and Css4 were truncated at their N and C termini, resulting in miniature peptides composed essentially of the core secondary structure motives. The truncated beta-toxins (DeltaDeltaBj-xtrIT and DeltaDeltaCss4) were non-toxic and did not compete with the parental toxins on binding at receptor site-4. Surprisingly, DeltaDeltaBj-xtrIT and DeltaDeltaCss4 were capable of modulating in an allosteric manner the binding and effects of site-3 scorpion alpha-toxins in a way reminiscent of that of brevetoxins, which bind at receptor site-5. While reducing the binding and effect of the scorpion alpha-toxin Lqh2 at mammalian sodium channels, they enhanced the binding and effect of LqhalphaIT at insect sodium channels. Co-application of DeltaDeltaBj-xtrIT or DeltaDeltaCss4 with brevetoxin abolished the brevetoxin effect, although they did not compete in binding. These results denote a novel surface at DeltaDeltaBj-xtrIT and DeltaDeltaCss4 capable of interaction with sodium channels at a site other than sites 3, 4, or 5, which prior to the truncation was masked by the bioactive surface that interacts with receptor site-4. The disclosure of this hidden surface at both beta-toxins may be viewed as an exercise in "reverse evolution," providing a clue as to their evolution from a smaller ancestor of similar scaffold.
Cohen
Lior
L
Department of Plant Sciences, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, Israel.
Lipstein
Noa
N
Karbat
Izhar
I
Ilan
Nitza
N
Gilles
Nicolas
N
Kahn
Roy
R
Gordon
Dalia
D
Gurevitz
Michael
M
D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D019143:Evolution, Molecular; D048188:Locusta migratoria; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D012604:Scorpion Venoms / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D017384:Sequence Deletion; D015222:Sodium Channels / Q000378:metabolism*; D013499:Surface Properties
D012604:Scorpion Venoms; D015222:Sodium Channels