Structural bases of TRP channel TRPV6 allosteric modulation by 2-APB

Transient receptor potential (TRP) channels are involved in various physiological processes, including sensory transduction. The TRP channel TRPV6 mediates calcium uptake in epithelia and its expression is dramatically increased in numerous types of cancer. TRPV6 inhibitors suppress tumor growth, but the molecular mechanism of inhibition remains unknown.

We have recently discovered a novel mechanism by which TRPV6 channels can be regulated by small molecules. There results have been published in the journal Nature Communications.

Despite previous studies that have shown the manner in which TRPV6 can open and close, it was unknown how this ion channel could be regulated by small molecules and potential therapeutics. Using a combination of X-ray crystallography, cryo-electron microscopy, and functional recordings of calcium flux through TRPV6 and other TRPV ion channels, we have identified a new ligand binding site by which these ion channels can be regulated.  More specifically, we have found a site distal to the pore, in which the small molecule 2-APB can bind. Binding of 2-APB displaces a tightly bound lipid-like molecule, and via allostery, or, in other words, the transmission of moment, displaces an activating lipid at a site proximal to the pore, which results in the breaking of two electrostatic bonds that stabilize the open state, and channel closure. This type of interplay between small regulatory molecules, membrane lipids, and an ion channel have not been observed before and bring to light not only a novel regulatory site, but also a never-before-seen mechanism that can be exploited to target TRPV6, and TRP channels in general, in disease.

Movie. Conformational changes in TRPV6 allosterically inhibited by 2-APB. A morph between open and 2-APB-bound closed states of human TRPV6 represented by the hTRPV6 and hTRPV6-Y467A_2-APB structures, respectively. Shown is the entire TRPV6 tetramer and the transmembrane domain of a single subunit viewed parallel to the membrane, and then the entire tetramer and the pore-forming region viewed intracellularly. Sticks represent 2-APB molecules (red), S1-S4 lipids (purple), activating lipids (magenta), residues contributing to the hydrophobic cluster (cyan), residues forming hydrogen bonds (dashed lines) that stabilize the open state (orange) and residues involved in 2-APB binding, and TRPV6 permeation.