Inter-residue coupling contributes to high-affinity subtype-selective binding of α-bungarotoxin to nicotinic receptors

Steven M. Sine, Sun Huang, Shu Xing Li, Corrie J.B. Dacosta, Lin Chen

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


The crystal structure of a pentameric α7 ligand-binding domain chimaera with bound α-btx (α-bungarotoxin) showed that of the five conserved aromatic residues in α7, only Tyr184 in loop C of the ligand-binding site was required for high-affinity binding. To determine whether the contribution of Tyr184 depends on local residues, we generated mutations in an α7/5HT3A (5-hydroxytryptamine type 3A) receptor chimaera, individually and in pairs, and measured 125I-labelled α-btx binding. The results show that mutations of individual residues near Tyr184 do not affect α-btx affinity, but pairwise mutations decrease affinity in an energetically coupled manner. Kinetic measurements show that the affinity decreases arise through increases in the α-btx dissociation rate with little change in the association rate. Replacing loop C in α7 with loop C from the α-btx-insensitive α2 or α3 subunits abolishes high-affinity α-btx binding, but preserves acetylcholine-elicited single channel currents. However, in both the α2 and α3 construct, mutating either residue that flanks Tyr184 to its α7 counterpart restores high-affinity α-btx binding. Analogously, in α7, mutating both residues that flank Tyr184 to the α2 or α3 counterparts abolishes high-affinity α-btx binding. Thus interaction between Tyr184 and local residues contributes to high-affinity subtype-selective α-btx binding.

Original languageEnglish (US)
Pages (from-to)311-321
Number of pages11
JournalBiochemical Journal
Issue number2
StatePublished - Sep 1 2013


  • Crystal structure
  • Inter-residue coupling
  • Molecular recognition
  • Neurotoxin
  • Nicotinic acetylcholine receptor

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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