Epithelial calcium channel TRPV6 is a member of the vanilloid subfamily of TRP channels that is permeable to cations and highly selective to Ca2+; it shows constitutive activity regulated negatively by Ca2+and positively by phosphoinositol and cholesterol lipids. In this review, we describe the molecular structure of TRPV6 and discuss how its structural elements define its unique functional properties. High Ca2+selectivity of TRPV6 originates from the narrow selectivity filter, where Ca2+ions are directly coordinated by a ring of anionic aspartate side chains. Divalent cations Ca2+and Ba2+permeate TRPV6 pore according to the knock‐off mechanism, while tight binding of Gd3+to the aspartate ring blocks the channel and prevents Na+from permeating the pore. The iris‐like channel opening is accompanied by an α‐to‐π helical transition in the pore‐lining transmembrane helix S6. As a result of this transition, the intracellular halves of the S6 helices bend and rotate by about 100 deg, exposing different residues to the channel pore in the open and closed states. Channel opening is also associated with changes in occupancy of the transmembrane domain lipid binding sites. The inhibitor 2‐aminoethoxydiphenyl borate (2‐APB) binds to TRPV6 in a pocket formed by the cytoplasmic half of the S1‐S4 transmembrane helical bundle and shifts open‐closed channel equilibrium towards the closed state by outcompeting lipids critical for activation. Ca2+inhibits TRPV6 via binding to calmodulin (CaM), which mediates Ca2+‐dependent inactivation. The TRPV6‐CaM complex exhibits 1:1 stoichiometry; one TRPV6 tetramer binds both CaM lobes, which adopt a distinct head‐to‐tail arrangement. The CaM C‐terminal lobe plugs the channel through a unique cation‐π interaction by inserting the side chain of lysine K115 into a tetra‐tryptophan cage at the ion channel pore intracellular entrance. Recent studies of TRPV6 structure and function described in this review advance our understanding of the role of this channel in physiology and pathophysiology and inform new therapeutic design.
Transient receptor potential vanilloid (TRPV) channels play various important roles in human physiology. As membrane proteins, these channels are modulated by their endogenous lipid environment as the recent wealth of structural studies has revealed functional and structural lipid binding sites. Additionally, it has been shown that exogenous ligands can exchange with some of these lipids to alter channel gating. Here, we used molecular dynamics simulations to examine how one member of the TRPV family, TRPV2, interacts with endogenous lipids and the pharmacological modulator cannabidiol (CBD). By computationally reconstituting TRPV2 into a typical plasma membrane environment, which includes phospholipids, cholesterol, and phosphatidylinositol (PIP) in the inner leaflet, we showed that most of the interacting surface lipids are phospholipids without strong specificity for headgroup types. Intriguingly, we observed that the C‐terminal membrane proximal region of the channel binds preferentially to PIP lipids. We also modelled two structural lipids in the simulation: one in the vanilloid pocket and the other in the voltage sensor‐like domain (VSLD) pocket. The simulation shows that the VSLD lipid dampens the fluctuation of the VSLD residues, while the vanilloid lipid exhibits heterogeneity both in its binding pose and in its influence on protein dynamics. Addition of CBD to our simulation system led to an open selectivity filter and a structural rearrangement that includes a clockwise rotation of the ankyrin repeat domains, TRP helix, and VSLD. Together, these results reveal the interplay between endogenous lipids and an exogenous ligand and their effect on TRPV2 stability and channel gating.
more » « less- Award ID(s):
- 2111728
- NSF-PAR ID:
- 10392278
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Protein Science
- Volume:
- 32
- Issue:
- 1
- ISSN:
- 0961-8368
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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