Crowding-induced opening of the mechanosensitive Piezo1 channel in silico

Abstract

Mechanosensitive Piezo1 channels are essential mechanotransduction proteins in eukaryotes. Their curved transmembrane domains, called arms, create a convex membrane deformation, or footprint, which is predicted to flatten in response to increased membrane tension. Here, using a hyperbolic tangent model, we show that, due to the intrinsic bending rigidity of the membrane, the overlap of neighboring Piezo1 footprints produces a flattening of the Piezo1 footprints and arms. Multiple all-atom molecular dynamics simulations of Piezo1 further reveal that this tension-independent flattening is accompanied by gating motions that open an activation gate in the pore. This open state recapitulates experimentally obtained ionic selectivity, unitary conductance, and mutant phenotypes. Tracking ion permeation along the open pore reveals the presence of intracellular and extracellular fenestrations acting as cation-selective sites. Simulations also reveal multiple potential binding sites for phosphatidylinositol 4,5-bisphosphate. We propose that the overlap of Piezo channel footprints may act as a cooperative mechanism to regulate channel activity.

An inter-channel cooperative mechanism mediates PIEZO1’s exquisite mechanosensitivity

“…Our mechanism is consistent with electrophysiology experiments showing collective PIEZO1 gating properties and imaging experiments revealing fluorescently-labeled PIEZO1 channels produce dense fluorescent puncta in cell membranes 17,23,30,31 . PIEZO1 puncta seemingly exhibit a large heterogeneity of size and intensity, suggesting they harbor a variable number of channels.…”

“…A central tenet of our cooperative mechanism states that PIEZO1 channels diffuse closer to each other when they are open as compared to when they are closed. To test this assumption, we used coarse-grained (CG) simulations to determine the minimal inter-channel distance between pairs of open or closed channels diffusing for ≈ 7 μs in a 52 x 104 nm membrane at 313 or 340 K. The spatial coordinates corresponding to the open and closed conformations were obtained from a recent computational study 17 . In CG simulations, the protein backbone is rigid, but proteins freely rotate and diffuse relative to lipid and solvent molecules.…”

Piezo1 ion channels inherently function as independent mechanotransducers

“…Moreover, this calculation likely represents a slight underestimate of the true channel density, owing to inactivation at negative potentials. Two groups had previously predicted that nearby Piezo1 channels may influence each other’s gating, even in the absence of membrane tension (Haselwandter and MacKinnon 2018, Jiang et al 2021). We therefore chose first to analyze the activity during the prepulse, which is designed to minimize resting membrane tension.…”

“…The energetic cost of this membrane curvature implies that Piezo1 channels that are within ~3 decay lengths (a “footprint” of ~50 nm; see Methods ) may influence each other via multiple mechanisms: opposing curvature may cause nearby Piezo1 channels to repel each other, as well as influence each other’s gating properties (Haselwandter and MacKinnon 2018). Indeed, imaging of vesicles containing reconstituted Piezo1 have demonstrated the ability of Piezo1 to curve the membrane locally and suggested that flattening of the channel dome may directly couple to channel opening, but the precise effects of membrane energetics on gating have yet to be explored experimentally (Lin et al 2019, Jiang et al 2021). Here, we set out to precisely quantify the spatial distribution and potential functional interactions of Piezo1 ion channels across multiple orders of channel densities.…”

Trends in Piezo Channel Research Over the Past Decade: A Bibliometric Analysis

“…Ceramide and sphingomyelin are determinants of native Piezo gating that enable sustained activity (Shi et al, 2020). Piezo channel activity also requires the presence of phosphoinositides (Borbiro et al, 2015;Buyan et al, 2020;Jiang et al, 2021). Piezo1 and Piezo2 channels can locally deform lipid membranes into a dome-like shape (Zhao et al, 2018;Wang et al, 2019).…”