Journal of Biological Chemistry
Volume 275, Issue 38, 22 September 2000, Pages 29594-29601
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PROTEIN STRUCTURE AND FOLDING
Molecular Determinants by Which a Long Chain Toxin from Snake Venom Interacts with the Neuronal α7-Nicotinic Acetylcholine Receptor*

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Long chain curarimimetic toxins from snake venom bind with high affinities to both muscular type nicotinic acetylcholine receptors (AChRs) (Kd in the pm range) and neuronal α7-AChRs (Kd in the nmrange). To understand the molecular basis of this dual function, we submitted α-cobratoxin (α-Cbtx), a typical long chain curarimimetic toxin, to an extensive mutational analysis. By exploring 36 toxin mutants, we found that Trp-25, Asp-27, Phe-29, Arg-33, Arg-36, and Phe-65 are involved in binding to both neuronal and Torpedo(Antil, S., Servent, D., and Ménez, A. (1999) J. Biol. Chem. 274, 34851–34858) AChRs and that some of them (Trp-25, Asp-27, and Arg-33) have similar binding energy contributions for the two receptors. In contrast, Ala-28, Lys-35, and Cys-26–Cys-30 selectively bind to the α7-AChR, whereas Lys-23 and Lys-49 bind solely to the Torpedo AChR. Therefore, α-Cbtx binds to two AChR subtypes using both common and specific residues. Double mutant cycle analyses suggested that Arg-33 in α-Cbtx is close to Tyr-187 and Pro-193 in the α7 receptor. Since Arg-33 of another curarimimetic toxin is close to the homologous αTyr-190 of the muscular receptor (Ackermann, E. J., Ang, E. T. H., Kanter, J. R., Tsigelny, I., and Taylor, P. (1998) J. Biol. Chem. 273, 10958–10964), toxin binding probably occurs in homologous regions of neuronal and muscular AChRs. However, no coupling was seen between α-Cbtx Arg-33 and α7 receptor Trp-54, Leu-118, and Asp-163, in contrast to what was observed in a homologous situation involving another toxin and a muscular receptor (Osaka, H., Malany, S., Molles, B. E., Sine, S. M., and Taylor, P. (2000)J. Biol. Chem. 275, 5478–5484). Therefore, although occurring in homologous regions, the detailed modes of toxin binding to α7 and muscular receptors are likely to be different. These data offer a molecular basis for the design of toxins with predetermined specificities for various members of the AChR family.

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Published, JBC Papers in Press, June 13, 2000, DOI 10.1074/jbc.M909746199

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