Agonist efficiency links binding and gating in a nicotinic receptor

Area of Science:

• Biochemistry
• Molecular Biology
• Pharmacology

Background:

• Receptors transition between resting (C) and active (O) states to signal.
• Agonist binding energy (O-C) determines maximum receptor response.
• Nicotinic receptors utilize efficiency (η) to link binding energy to gating.

Purpose of the Study:

• To investigate the relationship between agonist binding energy and receptor gating efficiency (η).
• To identify distinct structural states of receptor binding sites based on efficiency classes.
• To elucidate how efficiency (η) calibrates allosteric transitions in proteins.

Main Methods:

• Analysis of concentration-response curves for 23 agonists across 53 receptor mutations.
• Estimation and classification of receptor gating efficiency (η) values.
• Correlation analysis between efficacy, affinity, and efficiency classes.

Main Results:

• Receptor efficiencies (η) sorted into five discrete classes: 0.56 (17%), 0.51 (32%), 0.45 (13%), 0.41 (26%), and 0.31 (12%).
• These classes imply the existence of five distinct C vs. O binding site structural pairs.
• Linear correlations between efficacy and affinity were observed within each class, masked by the presence of multiple classes.

Conclusions:

• Gating efficiency (η) serves as a crucial link between agonist binding and receptor activation.
• The identified efficiency classes provide evidence for multiple structural conformations of the receptor binding site.
• Efficiency (η) calibrates a key step in the allosteric transition pathway of the receptor protein.