Abstract
TRPA1 (transient-receptor-potential-related ion channel with ankyrin domains) is a direct receptor or indirect effector for a wide variety of nociceptive signals, and thus is a compelling target for development of analgesic pharmaceuticals such as channel blockers. Recently, the structure of TRPA1 was reported, providing insights into channel assembly and pore architecture. Here we report whole-cell and single-channel current recordings of wild-type human TRPA1 as well as TRPA1 bearing point mutations of key charged residues in the outer pore. These measurements demonstrate that the glutamate at position 920 plays an important role in collecting cations into the mouth of the pore, by changing the effective surface potential by ~16 mV, while acidic residues further out have little effect on permeation. Electrophysiology experiments also confirm that the aspartate residue at position 915 represents a constriction site of the TRPA1 pore and is critical in controlling ion permeation.
Highlights
TRPA1, the only mammalian member of the TRPA subfamily of the transient receptor potential (TRP) ion channel family, is highly expressed in dorsal root and trigeminal ganglion neurons
In a TRPV1 structure in complex with DkTx and RTX, the pore helix extending from the outer end of the fifth transmembrane domain towards the center of the pore terminates at a glycine at position 643 (G643); at the bend, M644 appears to create a constriction at the inner end of an apparent selectivity filter (Fig 1A) [27]
We can use blocker affinity to calculate the change in electrostatic potential at the blocking site caused by the E920A mutation, because the ratio of the blocker dissociation constants varies with both the charge of the blocker, z, and the change in the surface potential Δφ at the blocking site [46]: KD;mut 1⁄4 eÀ zFD;=RT
Summary
TRPA1, the only mammalian member of the TRPA subfamily of the transient receptor potential (TRP) ion channel family, is highly expressed in dorsal root and trigeminal ganglion neurons. There, it has a variety of sensory roles, especially sensation of painful or irritating stimuli [1,2,3,4,5,6,7,8,9,10]. Many irritating chemicals activate TRPA1 through covalent modification of cysteine residues in its N-terminus [12, 24]. Menthol is an exception in that it activates TRPA1 by PLOS ONE | DOI:10.1371/journal.pone.0166167 November 8, 2016
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