TRPM3 is an ion channel belonging to the transient receptor potential (TRP) channel family. In the dorsal root ganglion, TRPM3 resides in nociceptor neurons, and its activation by noxious stimuli such as heat leads to pain sensation. To relieve pain, morphine activates μ-opioid receptors (a class of G-protein-coupled receptors, or GPCRs (blue)), leading to the accumulation of free Gβγ proteins (yellow and red) on the cell membrane. These Gβγ proteins can directly interact with TRPM3, inhibit TRPM3 activity, and reduce pain. The inhibitory effect of Gβγ on TRPM3 (purple) leads to reduced neuronal excitability, functionally converging with the activating effect of Gβγ on another ion channel target, the GIRK channel (green).

         Using electrophysiology in cells, I have determined the apparent affinity between Gβγ and TRPM3 to be ~200 nM. This affinity is ~10,000-fold higher than the affinity between Gβγ and the GIRK channel, suggesting vastly different regulation principles of TRPM3 and GIRK channels by GPCRs. Using cryo-electron microscopy (cryo-EM), I determined the structures of TRPM3 channel by itself, in complex with an activating lipid PIP2, as well as in complex with Gβγ. However, in the structures, Gβγ only loosely associates with TRPM3, in contrast to the high-affinity interactions observed in cells. Apparently, things are different when TRPM3 channels are isolated from the cell membrane by detergent. What are the missing links? Is the lipid bilayer membrane itself crucial to the conformation of the TRPM3 channel? Are there specific lipid molecules in the cell membrane essential for TRPM3-Gβγ interactions? Are there native protein partners of TRPM3 important for its engagement with Gβγ? My research group will continue pursuing the molecular mechanism of TRPM3 function and regulation.