High‐voltage‐activated calcium (CaV1/CaV2) channels translate action potentials into Ca2+influx in excitable cells to control essential biological processes that include; muscle contraction, synaptic transmission, hormone secretion and activity‐dependent regulation of gene expression. Modulation of CaV1/CaV2 channel activity is a powerful mechanism to regulate physiology, and there are a host of intracellular signalling molecules that tune different aspects of CaVchannel trafficking and gating for this purpose. Beyond normal physiological regulation, the diverse CaVchannel modulatory mechanisms may potentially be co‐opted or interfered with for therapeutic benefits. CaV1/CaV2 channels are potently inhibited by a four‐member sub‐family of Ras‐like GTPases known as RGK (Rad, Rem, Rem2, Gem/Kir) proteins. Understanding the mechanisms by which RGK proteins inhibit CaV1/CaV2 channels has led to the development of novel genetically encoded CaVchannel blockers with unique properties; including, chemo‐ and optogenetic control of channel activity, and blocking channels either on the basis of their subcellular localization or by targeting an auxiliary subunit. These genetically encoded CaVchannel inhibitors have outstanding utility as enabling research tools and potential therapeutics.
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.
- NSF-PAR ID:
- 10368805
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- The Journal of Physiology
- Volume:
- 599
- Issue:
- 10
- ISSN:
- 0022-3751
- Page Range / eLocation ID:
- p. 2673-2697
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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