A single TRPV1 amino acid controls species sensitivity to capsaicin

Abstract

Chili peppers produce capsaicin, the principle chemical that accounts for the culinary sensations of heat. Capsaicin activates the transient receptor potential cation channel subfamily V member 1 (TRPV1) on sensory neurons to alter the membrane potential to induce pain. While structural studies have identified residues important for the binding of capsaicin to rat TRPV1, there is still no clear understanding of differential capsaicin sensitivity of TRPV1 between birds and mammals. To determine the residues dictating relative capsaicin sensitivity among species, we have used intracellular Ca2+ imaging to characterize chimeras composed of capsaicin-sensitive rat TRPV1 (rTRPV1) and capsaicin-insensitive chicken TRPV1 (cTRPV1) with a series of capsaicinoids. We find that chimeras containing rat E570-V686 swapped into chicken receptors displays capsaicin sensitivity, and that a single amino acid substitution in the S4-S5 helix, changing the alanine at position 578 in the chick receptor to a glutamate, is sufficient to endow micromolar capsaicin sensitivity. Moreover, introduction of lysine, glutamine or proline at A578 also install capsaicin sensitivity in cTRPV1. Comparing the derivatives Cap-EA and Cap-EMA with capsaicin, these two compounds with the hydrophilic vanilloid-like moiety affect the protein-ligand interaction. The ability of 10 M Cap-EA to activate cTRPV1-A578E and the differential response of mutants to the analogs suggests that chick A578 may participate in vanilloid binding, as does the corresponding rTRPV1 site. The hydrophilic vanilloid agonist zingerone 500 M failed to activate any A578 mutants that retained capsaicin sensitivity, suggesting that the vanilloid group alone is not sufficient for receptor activation. Replacing the rTRPV1-E570 residue with K, Q shows a similar tendency to maintain the receptor capsaicin sensitivity. Our study demonstrates a subtle modification on different species TRPV1 globally alter their capsaicin response.