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bioRxiv · 10.1101/2021.03.25.437100

Structures of TRPM5 channel elucidate mechanism of activation and inhibition

Lu, W.·Du, J.·Ruan, Z.·Haley, E.·Orozco, I.·Roth, R.·Sabat, M.·Myers, R.
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Abstract

The Ca2+-activated TRPM5 channel plays an essential role in the perception of sweet, bitter, and umami stimuli in type II taste cells and in insulin secretion by pancreatic beta cells1-3. Interestingly, the voltage dependence of TRPM5 in taste bud cells depends on the intracellular Ca2+ concentration4, yet the mechanism remains elusive. Here we report cryo-electron microscopy structures of the zebrafish TRPM5 in an apo closed state, a Ca2+-bound open state, and an antagonist-bound inhibited state, at resolutions up to 2.3 [A]. We defined two novel ligand binding sites: a Ca2+ binding site (CaICD) in the intracellular domain (ICD), and an antagonist binding site in the transmembrane domain (TMD) for a drug (NDNA) that regulates insulin and GLP-1 release5. The CaICD site is unique to TRPM5 and has two roles: shifting the voltage dependence toward negative membrane potential, and promoting Ca2+ binding to the CaTMD site that is conserved throughout Ca2+-sensitive TRPM channels6. Replacing glutamate 337 in the CaICD site with an alanine not only abolished Ca2+ binding to CaICD but also reduced Ca2+ binding affinity to CaTMD, suggesting a cooperativity between the two sites. We have defined mechanisms underlying channel activation and inhibition. Conformational changes initialized from both Ca2+ sites, 70 [A] apart, are propagated to the ICD-TMD interface and cooperatively open the ion-conducting pore. The antagonist NDNA wedges into the space between the S1-S4 domain and pore domain, stabilizing the TMD in an apo-like closed state. Our results lay the foundation for understanding the voltage-dependent TRPM channels and developing new therapeutic agents to treat metabolic disorders.

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Lu, W., Du, J., Ruan, Z., Haley, E., Orozco, I., Roth, R., Sabat, M., Myers, R.. 2021-03-26. Structures of TRPM5 channel elucidate mechanism of activation and inhibition. https://doi.org/10.1101/2021.03.25.437100

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