Conformational Dynamics In TRPV1 Channels Reported By An Encoded Coumarin Amino Acid

Transient Receptor Potential Vanilloid (TRPV1) channels support the detection and integration of nociceptive input. Currently available functional and structural data suggest that that TRPV1 channels have two potential gates within their cation selective permeation pathway: a barrier formed by a bundle crossing at the intracellular entrance and a second constriction created by the ion selectivity filter. To describe conformational changes associated with channel gating within the pore, the fluorescent non-canonical amino acid (f- ncAA) coumarin-tyrosine was genetically encoded at Y671, a residue proximal to the selectivity filter. TRPV1 channels expressing coumarin at either site displayed normal voltage- and agonist-dependent gating. Next, total internal reflection microscopy (TIRF) was performed to enable ultra-rapid, millisecond imaging of the conformational dynamics in single TRPV1 channels in live cells. Here, the data obtained from channels expressed in human derived cells show that optical fluctuations, photon counts, and variance of noise analysis from Y671 coumarin encoded in TRPV1 tetramers correlates closely with channel activation by capsaicin, thus providing an direct optical marker of channel activation at the selectivity filter. In companion molecular dynamics simulations, Y671 displays alternating solvent exposure between the closed and open states, giving support to the optical data. These calculations further suggest a direct involvement of Y671 in controlling the relative position of the pore helix and its role in supporting ionic conductance at the TRPV1 selectivity filter.