UC Davis

Ligand activation of the nociceptive TRPV1 ion channel by vanilloids is a proven and powerful pathway for pain management and serves as one of the best model systems for analyzing allosteric coupling in ion channels. However, vanilloid binding and activation have been mostly described only qualitatively in the past. We developed a novel method to isolate channel gating states with a specific number of bound ligands and bound configuration, which allowed direct measurement of binding affinity and gating energetics on a per subunit basis. We determined that capsaicin binds to a rat TRPV1 subunit with an association constant of 2.4X10^6 M^(-1), and found ligand binding to each subunit is nearly independent. Each ligand binding contributes 1.70 to 1.86 kcal/mol activation energy. Subunit contributions are nearly equal as postulated in the MWC model, with a minor deviation that two capsaicin molecules bound to diagonal subunits yield stronger cooperativity (by 0.3 to 0.4 kcal/mol) than those bound to neighboring subunits.