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Molecule of the Month: Capsaicin Receptor TRPV1

TRPV1 is an ion channel that senses heat and contributes to pain sensation.

TRPV1 bound to capsazepine (magenta). The location of the membrane is shown schematically in gray.

Have you ever wondered why some peppers taste hot? Spicy plants contain noxious chemicals that protect them, such as capsaicin in chili peppers and piperine in black pepper. Amazingly, TRPV1 is an ion channel that opens when activated by molecules like capsaicin, or when the temperature gets very hot. So, it contributes to our ability to sense both heat and spicy food, triggering similar sensations.

Hot Stuff

TRPV1 is part of a large superfamily of transient receptor potential (TRP) ion channels that respond to a wide array of physical and chemical stimuli, including cold, cooling agents like menthol, acidity, and bioactive lipids. TRP channels have similar overall structures with four identical subunits that form a channel that opens and closes in response to a particular stimulus, letting cations flow across the membrane. The “V” in TRPV1 refers to “vanilloid” molecules such as capsaicin that bind to the protein.

CryoEM and Nanodiscs

PDB entry 5is0 shows TRPV1 bound to a molecule that resembles capsaicin. The molecule binds in a pocket between subunits, near one of the gates that control ion flux through the channel pore. This structure was determined by purifying the channel and inserting it into lipid nanodiscs, which were then examined using electron cryo-microscopy. If you look at the cryoEM maps at the EMDataBank (EMD-8119), you can see the lipid nanodisc surrounding the membrane-spanning portion of the protein.

TRPV5 bound to calmodulin (orange, with calcium ions in red).

Download high quality TIFF image

Collecting Calcium

The TRPV5 channel plays a slightly different role. It is found in the kidneys where it helps to reabsorb calcium so that we don't excrete it. Unlike TRPV1, TRPV5 is usually open, allowing calcium to flow back into kidney cells from the urine. But, if the amount of calcium gets too high, the calcium-sensing protein calmodulin is recruited to the TRPV5 channel to stop the flow of calcium into the cell, as seen here in PDB entry 6dmw.

Closed and Open TRPV1

Cryoelectron microscopy has allowed researchers to capture TRP channels in many different states. PDB entry 5irz is the closed TRPV1 channel, with several rings of amino acids forming constrictions that block the ion pore. In 5irx, the channel is held open by the binding of two toxins (shown in purple and magenta), shifting the location of these amino acids to open the ion conducting pathway. To explore these structures in more detail, click on the image for an interactive JSmol.

Topics for Further Discussion

Structures for many TRP channels are available in the PDB archive, try searching for "TRP channel" at the main RCSB PDB site to explore them.
Many other ion channels are composed of a ring of subunits or domains. Compare the structure of the TRP channel with, for example, Piezo1 channels, potassium channels, and mechanosensitive channels.

Related PDB-101 Resources

References

Pumroy, R.A., Fluck, E.C., Ahmed, T., Moiseenkova-Bell, V.Y. (2002) Structural insights into the gating mechanisms of TRPV channels. Cell Calcium 87: 102168.
van Goor, M.K., de Jager, L., Cheng, Y., van der Wijst, J. (2020) High-resolution structures of transient receptor potential vanilloid channels: Unveiling a functionally diverse group of ion channels. Prot. Sci. 29: 1569-1580.
6dmw: Hughes, T.E.T., Pumroy, R.A., Yazici, A.T., Kasimova, M.A., Fluck, E.C., Huynh, K.W., Samanta, A., Molugu, S.K., Zhou, Z.H., Carnevale, V., Rohacs, T., Moiseenkova-Bell, V.Y. (2018) Structural insights on TRPV5 gating by endogenous modulators. Nat Commun 9: 4198-4198
5is0, 5irx, 5irz: Gao, Y., Cao, E., Julius, D., Cheng, Y. (2016) TRPV1 structures in nanodiscs reveal mechanisms of ligand and lipid action. Nature 534: 347-351
Venkatachalam, K., Montell, C. (2007) TRP channels. Annu Rev Biochem 76: 387-417.

October 2020, David Goodsell

http://doi.org/10.2210/rcsb_pdb/mom_2020_10