TMEM150C/Tentonin3 Is a Regulator of Mechano-gated Ion Channels

A hydrophobic gate in the inner pore helix is the major determinant of inactivation in mechanosensitive Piezo channels

Piezo1 and Piezo2 belong to a family of mechanically-activated ion channels implicated in a wide range of physiological processes. Mechanical stimulation triggers Piezo channels to open, but their characteristic fast inactivation process results in rapid closure. Several disease-causing mutations in Piezo1 alter the rate of inactivation, highlighting the importance of inactivation to the normal function of this channel. However, despite the structural identification of two physical constrictions within the closed pore, the mechanism of inactivation remains unknown. Here we identify a functionally conserved inactivation gate in the pore-lining inner helix of mouse Piezo1 and Piezo2 that is distinct from the two constrictions. We show that this gate controls the majority of Piezo1 inactivation via a hydrophobic mechanism and that one of the physical constrictions acts as a secondary gate. Our results suggest that, unlike other rapidly inactivating ion channels, a hydrophobic barrier gives rise to fast inactivation in Piezo channels.

Functional analyses of heteromeric human PIEZO1 Channels

PIEZO1 and PIEZO2 are mechanosensitive channels (MSCs) important for cellular function and mutations in them lead to human disorders. We examined how functional heteromers form between subunits of PIEZO1 using the mutants E2117K, E2117D, and E2117A. Homomers of E2117K do not conduct. E2117A homomers have low conductance with rapid inactivation, and those of E2117D have high conductance with slow inactivation. Pairing E2117K with E2117D or E2117A with E2117D gave rise to new channel species representing heteromers with distinct conductances. Whole-cell currents from co-expression of E2117A and E2117D fit well with a linear-combination model of homomeric channel currents suggesting that functional channels do not form from freely-diffusing, randomly-mixed monomers in-vitro. Whole-cell current from coexpressed PIEZO1/PIEZO2 also fit as a linear combination of homomer currents. High-resolution optical images of fluorescently-tagged channels support this interpretation because coexpressed subunits segregate into discrete domains.