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Pairwise interactions between neuronal alpha7 acetylcholine receptors and alpha-conotoxin ImI
P A Quiram1, J J Jones, S M Sine
1Receptor Biology Laboratory, Department of Physiology and Biophysics Mayo Foundation, Rochester, Minnesota 55905, USA.
The Journal of Biological Chemistry
|July 3, 1999
Summary
Alpha-conotoxin ImI (CTx ImI) binding to alpha7 nicotinic acetylcholine receptors reveals key interactions. Tyr-195 in alpha7 forms a dominant interaction with CTx ImI, anchoring the toxin and defining its orientation.
Area of Science:
- Neuroscience
- Biochemistry
- Molecular Biology
Background:
- Neuronal alpha7 nicotinic acetylcholine receptors are crucial for neurotransmission.
- Alpha-conotoxin ImI (CTx ImI) is a selective ligand for these receptors.
Purpose of the Study:
- To identify key residues in alpha7 nicotinic acetylcholine receptors that bind CTx ImI.
- To elucidate the stabilizing interactions between CTx ImI and the receptor using mutant cycles analysis.
Main Methods:
- Mutagenesis of key residues in alpha7 receptor loops forming the ligand binding site.
- Competition binding assays using 125I-alpha-bungarotoxin.
- Thermodynamic mutant cycles analysis of receptor and toxin mutations.
Main Results:
- Tyr-195 in alpha7 predominantly contributes to CTx ImI affinity, with smaller contributions from Thr-77, Tyr-93, Asn-111, Gln-117, and Trp-149.
- A dominant interaction exists between Arg-7 of CTx ImI and Tyr-195 of alpha7.
- Multiple weak interactions were identified between CTx ImI (Asp-5, Trp-10) and alpha7 residues (Trp-149, Tyr-151, Gly-153, Thr-77, Asn-111).
Conclusions:
- The study establishes the orientation of CTx ImI within the alpha7 receptor binding site.
- Key residues and their interactions stabilizing the receptor-conotoxin complex are identified.
- Close proximity of residues on opposing faces of the alpha7 binding site is demonstrated.