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This Sandbox is Reserved from 26/11/2020, through 26/11/2021 for use in the course "Structural Biology" taught by Bruno Kieffer at the University of Strasbourg, ESBS. This reservation includes Sandbox Reserved 1643 through Sandbox Reserved 1664.

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The Transient Receptor Potential cation channel subfamily V member 1 TRPV1

Structure of TRPV1 in complex with capsazepine, determined in lipid nano disc, capsazepine is a synthetic antagonist of capsaicin

Drag the structure with the mouse to rotate

1 Introduction
2 Structure of TRPV1
3 Relation structure-function
- 3.1 Activators
  - 3.1.1 Capsaicin
  - 3.1.2 Resiniferatoxin (RTX)
- 3.2 Regulation
  - 3.2.1 Sensitization
  - 3.2.2 Desensitization
4 Implication of TRPV1 in the treatment of pain

Introduction

TRPV1 (Vanilloid Transient Receptor Potential Type 1) is a non-selective ion channel which, in response to a stimulus, induces an incoming current of cations, primarily calcium and sodium, causes depolarization of the cell. It is part of the TRP (Transient Receptor Potential) superfamily and is the first in a subfamily of vanilloid-sensitive TRP channels / channels: TRPVs. This receptor is expressed by sensory neurons of the dorsal and trigeminal spinal ganglia.TRPV1 is implicated in nociception, its activation by heat or by chemical substances leads to a painful sensation.^[1]

Structure of TRPV1

Schematic figure of the TRPV1 receptor

The TRPV1 receptor is a transmembrane protein receptor. It is made up of 839 amino acids. It’s molecular weight is 94 938Da.^[2] TRPV1 exists in two states : the open state and the closed state.^[3] TRPV1 are tetrameric channel type receptors. The four subunits form a symmetry plane around a pore allowing the passage of ions. Each TRPV1 subunits is made of one N-terminal tail, one transmembrane region, a C-terminal tail preceded by a TRP domain. The N-terminal and C-terminal region are intracellular. N and C terminal region are responsible of 70% of the total mass of TRPV1.^[2]

The region has 6 repeats of .^[2]^[4]

The transmembrane region is composed of six transmembrane a helices (,,,,,). S1,S2 and S3 helices contain aromatic side chain ().^[2] A small hydrophobic domain beetween S5 and S6 with a constitutes the pore allowing the passage of ions through the TRPV1 receptor.^[1]^[2]

Threonin residue () and Tyrosin residue () located on the fifth and the third transmembrane helices are very conserved. Threonin 550 and Tyrosin 511 are implicated in TRPV1 activation by vanilloids and in pain sensation.^[5]

The S6 domain links the receptor to the domain of TRPV1. The C-terminal is made of 150 amino acids and it contains .^[4].The TRP domain is made of 23-25 aminoacids with a alpha helical structure, it is found in many TRP family members.^[2] TRP domain is necessary for the formation of tetrameric TRPV1.

Many amino-acids of the C-terminal domain are the target of post-translationnal modifications by kinases and phosphatases.^[6]

Relation structure-function

TRPV1 is a homotetramer in which each subunit has several phosphorylation sites for PKA (protein kinase A), PKC (protein kinase C) and CaMkII (Ca2 + / calmodulin-dependent kinase II), as well as numerous glycosylation sites. These domains play a crucial role in the regulation of TRPV1 activity. The state of the channel is modulated by two types of molecules: agents that promote its opening of the channel, called agonists, and agents that induce its closure or prevent its opening, called antagonists.

Activators

Capsaicin

Chemical structure of capsaicin

Capsaicin is an active compound in chili. TRPV1 receptor has a capsaicin-binding pocket formed by S3,S4 and . The capsaicin-binding pocket is surrounded by the residues .^[7]

Bound capsaicin is oriented in a « tail-up, head down » configuration. In this configuration,capsaicin is anchored into the receptor.^[8]

The capsaicin cycle binds via hydrogen bounds to amino acids on the S3 helix (), on the and on the S6 helix (). The amid group of capsaicin binds the helix.^[4].

Capsaicin maintains TRPV1 in an open state. A conformational change wave spread over the whole pore.^[9]. This leads to the massive enter of Ca2+ and Na+ and the depolarization of the nerve fiber. Depolarization triggers the generation of an action potential causing a painful sensation.^[1]

Resiniferatoxin (RTX)

Chemical structure of resiniferatoxine

Resiniferatoxin is a natural analogue of capsaicin. It is the most potent TRPV1 agonist known, with a binding affinity for TRPV1 ~500x higher than that of capsaicin. Stimulation by resiniferatoxin makes this ion channel permeable to cations, especially calcium.

The pocket size characteristics of the TRPV1-RTX allow the installation of large structures such as the RTX : The sub-pocket near is shallow in the TRPV1-RTX because and are close and is oriented towards the vanilloid pocket.^[10]

The sub-pocket near , and is wide due to the projection of these amino acids out of the vanilloid pocket. This sub-pocket accommodates the diterpene group of the RTX.^[10]

However, the orientation of and makes this region of the vanilloid pocket narrow, which considerably limits the nature of the fragments tolerated.^[10]

The aromatic part of resiniferatoxin is located deeper in the sub-pocket near and is oriented almost parallel to the aromatic side chain of , so it establishes a strong interaction π-π. The aromatic hydroxyl and methoxy groups of the RTX form strong hydrogen bonds with , and . The ester group is linked to and by hydrogen bonds.

Regulation

Sensitization

Phosphorylation of the TRPV1 receptor leads to its sensitization. Phosphorylations are either caused by PKC (IP3 signalling), by PKA (AMPc signalling), or by CamKII.^[11]^[4]. The phosphorylation of TRPV1 lead to an over-expression of TRPV1 at the membrane surface.^[12] Moreover, phosphorylated TRPV1 would have a reduced channel opening threshold.^[13]. As a result phosphorylated TRPV1 are more responsive to agonist and the resulting pain sensation is higher.

PKA phosphorylates , PKC and CaMKII phosphorylate .

Desensitization

A repeated exposure of TRPV1 to capsaicin fails to activate the receptor. It occurs by a CA2+-dependent mechanism that leads to a desphosphorylation by the calcineurin phosphatase of the serine and threonine residues which have been previously phosphorylated by PKA (). Thus, the decrease in TRPV1 phosphorylation diminish the sensitivity of the capsaicin channel and leads to a decrease in capsaicin's response by negative feedback. The over-stimulation of TRPV1 is followed by the nerve endings' death due to calcium overload, causing analgesia.

Implication of TRPV1 in the treatment of pain

In 2011 Qutenza (NeurogesX) patch containing 8% of capsaicin has been markered in France and indicated in the neuropathic pain. The absorption through the skin of these creams generated partial desensitization of the nerve endings. This is the cause of a decrease in painful sensations.^[14]

Many laboratories are conducting clinical studies on oral TRPV1 antagonists: GlaxoSmithKline, Amgen, Merk-Neurogen, Abbot, Eli-Lilly-Glenmark, AstraZeneca and Japan Tobacco. The major problem with these pain relievers is the hyperthermia generated in humans. These effects caused these studies to be stopped in phase I.^[14]

References

↑ ^1.0 ^1.1 ^1.2 Wikipedia contributors. (2020b, décembre 21). TRPV1. Wikipedia. https://en.wikipedia.org/wiki/TRPV1 (Consulté le: déc. 28, 2020). [En ligne].
↑ ^2.0 ^2.1 ^2.2 ^2.3 ^2.4 ^2.5 Liao, M., Cao, E., Julius, D., & Cheng, Y. (2013b). Structure of the TRPV1 ion channel determined by electron cryo-microscopy. Nature, 504(7478), 107‑112. https://doi.org/10.1038/nature12822(consulté le déc. 28, 2020)
↑ T. Rosenbaum et S. A. Simon, « TRPV1 Receptors and Signal Transduction », in TRP Ion Channel Function in Sensory Transduction and Cellular Signaling Cascades, W. B. Liedtke et S. Heller, Éd. Boca Raton (FL): CRC Press/Taylor & Francis, 2007
↑ ^4.0 ^4.1 ^4.2 ^4.3 G. Smutzer et R. K. Devassy, « Integrating TRPV1 Receptor Function with Capsaicin Psychophysics », Advances in Pharmacological Sciences, janv. 14, 2016
↑ R. Kumar, A. Hazan, A. Basu, N. Zalcman, H. Matzner, et A. Priel, « Tyrosine Residue in the TRPV1 Vanilloid Binding Pocket Regulates Deactivation Kinetics », J. Biol. Chem., vol. 291, no 26, p. 13855‑13863, juin 2016, doi: 10.1074/jbc.M116.726372.
↑ X. Yao, H.-Y. Kwan, et Y. Huang, « Regulation of TRP Channels by Phosphorylation », Neurosignals, vol. 14, no 6, p. 273‑280, 2005, doi: 10.1159/000093042
↑ F. Yang et J. Zheng, « Understand spiciness: mechanism of TRPV1 channel activation by capsaicin », Protein Cell, vol. 8, no 3, p. 169‑177, mars 2017, doi: 10.1007/s13238-016-0353-7.
↑ F. Yang et al., « Structural mechanism underlying capsaicin binding and activation of the TRPV1 ion channel », Nat. Chem. Biol., vol. 11, no 7, Art. no 7, juill. 2015, doi: 10.1038/nchembio.1835.
↑ F. Yang et al., « The conformational wave in capsaicin activation of transient receptor potential vanilloid 1 ion channel », Nat. Commun., vol. 9, no 1, Art. no 1, juill. 2018, doi: 10.1038/s41467-018-05339-6.
↑ ^10.0 ^10.1 ^10.2 K. Elokely et al., « Understanding TRPV1 activation by ligands: Insights from the binding modes of capsaicin and resiniferatoxin », Proc. Natl. Acad. Sci., vol. 113, no 2, p. E137‑E145, janv. 2016, doi:10.1073/pnas.1517288113.
↑ K. W. Ho, N. J. Ward, et D. J. Calkins, « TRPV1: a stress response protein in the central nervous system », Am. J. Neurodegener. Dis., vol. 1, no 1, p. 1‑14, avr. 2012.
↑ K. W. Ho, N. J. Ward, et D. J. Calkins, « TRPV1: a stress response protein in the central nervous system », Am. J. Neurodegener. Dis., vol. 1, no 1, p. 1‑14, avr. 2012.
↑ G. Bhave et al., « Protein kinase C phosphorylation sensitizes but does not activate the capsaicin receptor transient receptor potential vanilloid 1 (TRPV1) », Proc. Natl. Acad. Sci., vol. 100, no 21, p. 12480‑12485, oct. 2003, doi: 10.1073/pnas.2032100100.
↑ ^14.0 ^14.1 A. Danigo, L. Magy, et C. Demiot, « TRPV1 dans les neuropathies douloureuses - Des modèles animaux aux perspectives thérapeutiques », médecine/sciences, vol. 29, no 6‑7, Art. no 6‑7, juin 2013, doi: 10.1051/medsci/2013296012.

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@@ Line 68: / Line 68: @@
 ====Desensitization====
-A repeated exposure of TRPV1 to capsaicin fails to activate the receptor. It occurs by a CA2+-dependent mechanism that leads to a '''desphosphorylation''' by the '''calcineurin''' [https://en.wikipedia.org/wiki/Phosphatase phosphatase] of the serine and threonine residues which have been previously phosphorylated by PKA. Thus, the decrease in TRPV1 phosphorylation diminish the sensitivity of the capsaicin channel and leads to a decrease in capsaicin's response by '''negative feedback'''.
+A repeated exposure of TRPV1 to capsaicin fails to activate the receptor. It occurs by a CA2+-dependent mechanism that leads to a '''desphosphorylation''' by the '''calcineurin''' [https://en.wikipedia.org/wiki/Phosphatase phosphatase] of the serine and threonine residues which have been previously phosphorylated by PKA (<scene name='86/868185/S502_t370/2'>S502 and T370</scene>). Thus, the decrease in TRPV1 phosphorylation diminish the sensitivity of the capsaicin channel and leads to a decrease in capsaicin's response by '''negative feedback'''.
 The '''over-stimulation''' of TRPV1 is followed by the nerve endings' death due to calcium overload, causing analgesia.