Structural elements in α-conotoxin ImI essential for binding to neuronal α7 receptors

Polly A. Quiram, Steven M. Sine

Research output: Contribution to journalArticlepeer-review

81 Scopus citations


The neuronal-specific toxin α-conotoxin ImI (CTx ImI) has the sequence Gly-Cys-Cys-Ser-Asp-Pro-Arg-Cys-Ala-Trp-Arg-Cys-NH2, in which each cysteine forms a disulfide bridge to produce a constrained two-loop structure. To investigate the structural basis for bioactivity we mutated individual residues in CTx ImI and determined bioactivity. Bioactivity of the toxins was determined by their competition against 125I-labeled α-bungarotoxin binding to homomeric receptors containing α7 sequence in the major extracellular domain and 5HT-3 sequence elsewhere. The results reveal two regions in CTx ImI essential for binding to the α7/5HT-3 receptor. The first is the triad Asp-Pro-Arg in the first loop, where conservative mutations of each residue diminish affinity by 2-3 orders of magnitude. The second region is the lone Trp in the second loop, where an aromatic side chain is required. The overall results suggest that within the triad of the first loop, Pro positions the flanking Asp and Arg for optimal interaction with one portion of the binding site, while within the second loop, Trp stabilizes the complex through its aromatic ring.

Original languageEnglish (US)
Pages (from-to)11007-11011
Number of pages5
JournalJournal of Biological Chemistry
Issue number18
StatePublished - May 1 1998

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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