28.20: Signal Transduction - Pressure

Search Fundamentals of Biochemistry

Learning Goals 

(Learning goals written by Claude, Sonnet 4.6, Anthropic)

Piezo Channel Architecture and Structural Domains

• Describe the extraordinary structural organization of Piezo1: explain how each of the three subunits in the homotrimeric, propeller-shaped complex contains 38 transmembrane segments organized as nine transmembrane helical units (THUs) forming curved peripheral blades, a central pore module consisting of the inner helix (IH), outer helix (OH), C-terminal extracellular domain (CED) cap, and C-terminal domain (CTD), and a 90 nm intracellular beam that bridges the distal blades to the central pore—and explain how the negatively charged DEEED patch in the cap ensures cation selectivity over anions, while E2495/E2496 in the CTD intracellular vestibule confer divalent Ca²⁺ selectivity.
• Explain the lever-like mechanotransduction model: describe how the curved peripheral blades act as mechanosensors, how the beam with residues L1342 and L1345 serving as the pivot acts as a lever that amplifies small displacements of the distal blades into opening of the central pore, and explain why positioning the pivot closer to the pore than to the blades provides mechanical amplification that converts large conformational changes in the blades into a relatively slight but cation-selective pore opening.
• Compare Piezo1 and Piezo2 in terms of tissue expression (Piezo1 in nonsensory tissues including lung, bladder, skin; Piezo2 predominantly in sensory tissues including DRG neurons and Merkel cells), sequence homology (~42%), and structural differences—noting that Piezo2 has additional constriction sites at L2743, F2754, and E2757 that form a transmembrane gate controlled by the cap domain, and an intrinsically disordered cytosolic plug adjacent to the beam that limits ion permeation in both channel types.

Mechanosensitive Gating, Inactivation, and Pharmacological Modulation

• Explain the membrane dome mechanism of Piezo channel activation: describe how Piezo channels in their closed state impose a dome-shaped curvature on the local lipid bilayer, storing potential energy in the curved membrane; how lateral membrane tension flattens this dome, expanding the channel's projected area and increasing system free energy; and how the resulting energy difference drives channel opening—and describe how the membrane footprint hypothesis extends this model by proposing that Piezo1 also deforms the surrounding membrane beyond its perimeter, further amplifying mechanosensitivity.
• Describe the three-state kinetic model of Piezo channel gating (open, closed, inactivated), explain how inactivation kinetics are voltage-dependent (fast at negative potentials, slow at positive potentials) and structurally determined by the C-terminal extracellular cap domain, IH, and CTD, and explain how gain-of-function mutations that slow inactivation (six identified in dehydrated hereditary xerocytosis) produce larger Ca²⁺ fluxes leading to disease—and identify additional modulators of inactivation kinetics including sphingomyelinase activity, membrane lipid composition, pH, temperature, and alternative splicing.
• Describe the pharmacological tools available for Piezo channel research: explain how Yoda1 acts as a molecular wedge lowering the mechanical activation threshold of Piezo1 (without efficiently activating Piezo2) while Jedi1/2 activates Piezo1 through the peripheral blade lever apparatus; how Dooku1 (a Yoda1 analog) antagonizes Yoda1-evoked activation; and how nonspecific blockers gadolinium, ruthenium red, and GsMTx4 (which may act by modulating local membrane tension rather than direct pore binding) inhibit Piezo1 currents.

Physiological Functions and Disease Relevance

• Describe the diverse physiological roles of Piezo channels: explain how Piezo1-mediated Ca²⁺ influx in red blood cells activates the Gardos channel (KCa3.1) to drive K⁺ and water efflux for volume regulation; how Piezo2 in DRG neurons and Merkel cells mediates light touch and proprioception; and explain how mutations in Piezo1 and Piezo2 cause hereditary diseases including dehydrated hereditary xerocytosis (gain-of-function Piezo1 mutations slowing inactivation), congenital lymphatic dysplasia, and muscular atrophy with perinatal respiratory distress.

This chapter section is taken in its entirety from Fang, XZ., Zhou, T., Xu, JQ. et al. Structure, kinetic properties, and biological function of mechanosensitive Piezo channels. Cell Biosci 11, 13 (2021). https://doi.org/10.1186/s13578-020-00522-z Creative Commons Attribution 4.0 International License, http://creativecommons.org/licenses/by/4.0/. We added iCn3D molecular models.

Introduction

Mechanotransduction, the conversion of mechanical stimuli into electrochemical signals, is essential for various biological processes, including neuronal cell development, pain sensation, and red blood cell volume regulation. As pivotal mechanosensors in mechanotransduction, mechanosensitive (MS) ion channels have been found in organisms from bacteria to mammals. Extensive studies have revealed a variety of ion channels in eukaryotic cells that can sense various forms of mechanical forces (Table \(\PageIndex{1}\)). These ion channels include transient receptor potential (TRP) channels and voltage-gated Na⁺, K^+, and Ca²⁺ channels, whose dysfunction may be associated with human genetic diseases. Notably, the MS candidates identified in invertebrates either have no homologs (e.g., TRPN) or no functional conservation (e.g., DEG/ENaC/ASIC) in mammals. Furthermore, most MS candidates (the TRP channel in particular) are activated not only by mechanical stimuli but also by chemicals, temperature, osmolarity, and heat (> 27–34 °C). Defining the molecular details of MS cation channels in mammals is paramount to understanding mechanotransduction and identifying novel therapeutic strategies for mechanosensitivity disorders.

Channel family	Channel isoforms	Ref.
TRP channels	TRPA1	[6]
	TRPC1	[7]
	TRPC6	[8]
	TRPV1	[9]
	TRPV4	[10]
	TRPM4	[11]
	TRPM7	[12]
	TRPN	[13]
	TRPP2	[14]
K ^+ channels	Shaker (Kv1.1)	[15]
	Ca^2^+-activated K^+ (BK)	[16]
	TREK1/2	[17]
	TRAAK	[18]
	HCN2	[19]
Na^+ channels	Nav1.5	[20]
Ca^2^+ channels	L-type	[21]
	N-type	[22]
	T-type	[23]
Cl^− channels	CFTR	[24]
OSCA protein family	ScCSC1, HsCSC1	[25]
DEG/ENaC superfamily	C.elegans MEC (MEC-4, MEC-10)	[26]
	ASIC	[27]
Other channels	TMC1/2	[28]

In 2010, Coste et al. revealed a novel family of mechanically activated (MA) cation channels in eukaryotes, comprising Piezo1 and Piezo2, which have been proposed as the long-sought-after MS ion channels in mammals. The Piezo1 channel is present in nonsensory tissues, with particularly high expression in the lung, bladder, and skin; by contrast, the Piezo2 channel is predominantly present in sensory tissues, such as dorsal root ganglia (DRG) sensory neurons and Merkel cells. Since their discovery, tremendous effort has been made to reveal the structures and biological functions of Piezo 1 and 2. The partial molecular structure of a Piezo channel was determined by cryo-electron microscopy (cryo-EM). Furthermore, Piezo channels have been linked to various pathological and physiological processes, including erythrocyte volume regulation, cell division, and innate immunity. Moreover, Piezo channel mutations are associated with multiple hereditary human diseases, such as autosomal recessive congenital lymphatic dysplasia, hereditary xerocytosis (a rare, autosomal dominant congenital hemolytic anemia characterized by macrocytic stomatocytosis and decreased red cell osmotic fragility due to a defect in cation permeability), and an autosomal recessive syndrome of muscular atrophy with perinatal respiratory distress. Considerable progress has been made in characterizing the structural features, physiological significance, and biophysical properties of Piezo proteins. Given the importance of Piezo channels in mechanotransduction, this review focuses on their structural features, kinetic properties, and potential roles as mechanosensors. We also briefly review the hereditary diseases caused by mutations in the Piezo genes, which are key to understanding their functions.

Structure of Piezo channels

Piezo proteins have an uncommonly large predicted size of approximately 2500 amino acids and encompass numerous transmembrane (TM) regions. Subsequent research has revealed that the mouse Piezo1 (mPiezo1) channel is an evolutionarily conserved pore-forming ion channel directly gated by membrane stretch. Several published cryo-EM studies have revealed that mPiezo1 exhibits a three-bladed, propeller-shaped homotrimeric structure that includes a central cap, three peripheral blade-like structures on the extracellular side, three long beams on the intracellular side that bridge the blades to the cap, and a TM region between these features, as shown in Figure \(\PageIndex{1}\).

Figure \(\PageIndex{1}\): Cryo-EM structure of the mPiezo1 channel (adapted from Zhao et al.). a. Multiple views of the sharpened map of the trimeric channel with the major domains labeled, with the three subunits colored red, green, and blue. b.  A cartoon model in which the three subunits are red, green, and blue. In the middle panel, the front subunit has been omitted to provide a better view of the curvature of the TMs

Structure of the Piezo1 channel

Unprecedented 38-TM topology

Piezo channels are predicted to possess an unusually large number of TM regions, ranging from 10 to 40. Zhao et al. recently produced high-resolution structures of mouse Piezo1 (mPiezo1), revealing a unique 38-TM topology in each subunit, as shown in Figure \(\PageIndex{2}\). The two TM regions (TM37 and TM38) closest to the center of the protein are designated as the inner helix (IH) and outer helix (OH), respectively, and enclose the transmembrane pore of the central pore module. The other 36 TM regions (TM1-36) form a curved, blade-like structure with nine repetitive folds, each containing 4 TM regions, called transmembrane helical units (THUs).

Figure \(\PageIndex{2}\): A 38-TM topology model and key functional sites in mPiezo1(adapted from Zhao et al.). a. A model showing one subunit with individual THUs and featured structural components. Red spheres indicate residues L1342 and L1345 in the beam. b. A 38-TM topology model color-coded to match the cartoon model in A

Figure \(\PageIndex{a}\) shows an interactive iCn3D model of the mouse mechanosensitive Piezo1 channel (5Z10) (long load time)

Figure \(\PageIndex{a}\): Mouse mechanosensitive Piezo1 channel (5Z10). (Copyright; author via source). Click the image for a popup or use this external link: https://structure.ncbi.nlm.nih.gov/i...ZcVpJczxvaaG79 (long load time)

Central cap

Kamajaya and colleagues employed topological prediction modeling. They found that residues 2210 to 2457 in Piezo1 form an extracellular loop following the last TM region from the C-terminus, defined as the C-terminal extracellular domain (CED) (Figure \(\PageIndex{1}\)). The deletion of residues 2218 to 2453 from the Piezo1 protein abolished expression of the central cap, suggesting that this region trimerizes to form the central cap (Figure \(\PageIndex{1}\) and Figure \(\PageIndex{3}\)). Further analysis revealed that the central cap consists of the CED in the form of a trimeric complex that encloses an extracellular vestibule (EV) with openings (Figure \(\PageIndex{3}\)).

Figure \(\PageIndex{3}\). Structure of the central pore module (adapted from Zhao et al. [35]). a. Ribbon diagram of the ion-conduction pore comprising the OH, CED, IH, and CTD from three color-coded subunits. The central solvent-accessible pathway is marked with a dotted mesh generated by the program HOLE. b. Pore module presenting the surface electrostatic potentials showing negative (red) and positive (blue) potential. Extracellular and intracellular fenestrations are marked by cyan and green dashed lines, respectively. Yellow dashed lines mark the lateral portal

Anchor

A hairpin structure, referred to as the anchor, connects the OH-IH pair to the C-terminal domain (CTD) plane, which moves the OH-CED-IH-containing region of one subunit into the neighboring subunit in a clockwise direction (Figure \(\PageIndex{1}\) and Figure \(\PageIndex{3}\)). The anchor comprises three helices (α1, α2, and α3). Helices α1 and α2 were found to organize into an inverted V-shaped structure, which maintains the integrity of the ion-conducting pore (Figure \(\PageIndex{2b}\)). In parallel with the membrane plane, the long α3 helix links to the OH via a lysine-rich anchor-OH linker that interacts with the polar residue-rich α2–3 turn in the anchor and the glutamate-rich region of the CTD. A few mutations in Piezo1 at locations including KKKK (2182-K2185), T2143, T2142 (T2127 in human Piezo1), R2514, E2523, and E2522, which are located in α3 in the anchor, have been reported to cause severe disease. Additionally, SERCA2, a Piezo-interacting protein, suppresses Piezo1 by acting on the anchor-OH linker. These findings support the structural and functional importance of the anchor region.

The long intracellular beam

On the intracellular surface, Piezo1 contains three beam-like structures 90 nm in length that are organized at a 30° angle relative to the membrane plane (Figure \(\PageIndex{1}\) and Figure \(\PageIndex{2}\)). Residues H1300-S1362 form the beam structure. The large intracellular THU7-8 loop, which contains approximately 390 residues, might provide the beam with the structural basis for mechanical transmission. Functionally, the three long intracellular beams support the whole TM skeleton and physically bridge the distal THUs to the central ion-conducting pore. When residues 1280 to 1360 (which form this beam structure) were deleted, the resulting mutant protein was absent, suggesting the structural importance of the beam.

Highly curved blades

The nine peripheral THUs in each subunit form blade-like structures, with each blade twisted clockwise (Figure \(\PageIndex{1b}\)). The proximal TM25–TM36 and peripheral TM13-24 interact at a 100° angle, as viewed from 90º relative to the plasma membrane plane, and a 140° angle from a line parallel to the plasma membrane plane. Another important feature of the blades is the L-shaped helical structures formed by TM13, TM17, TM21, TM25, and TM29. Both identifiable structural features appear to be ideal not only for mechanosensation but also for inducing local membrane curvature. Intriguingly, the peripheral TM13-24 appears to be within a highly curved membrane plane, indicating that the Piezo1 channel can curve the membrane in which it resides. This is consistent with past studies implying that Piezo1 ion channels can be regulated by cellular membrane curvature and tension.

The ion-conducting pathway

As pore-forming ion channels, Piezo proteins contain a trimeric ion-conducting channel made up of residues 2,189 to 2,547, which contain the last two TMs (Figure \(\PageIndex{3}\)). The continuous central channel consists of three parts: an EV within the cap region, a transmembrane vestibule (MV) within the membrane, and an intracellular vestibule (IV) underneath the membrane. The EV and IV have an opening that connects to the MVs, which are positioned above and below the membrane. Importantly, DEEED (2393–2397), a patch of negatively charged residues residing in the opening of the extracellular “cap” structure consisting of the CED, is required to ensure efficient ion conduction and determine the selection of cations over anions. Additionally, two critical acidic residues, E2495 and E2496, located at the CTD-constituted IV, may be responsible for divalent calcium ion selectivity, unitary conductance, and pore blockage.

Structure of the Piezo2 channel

Like Piezo1 channels, Piezo2 channels are large membrane proteins with over 2,800 residues. However, the Piezo2 and Piezo1 channels share only approximately 42% sequence homology. Recent studies have shown that the overall structure of the Piezo2 channel is very similar to that of Piezo1 in that it forms a three-bladed, propeller-like homotrimeric structure comprising a central ion-conducting pore module and three peripheral blades with 38 TMs.

Figure \(\PageIndex{b}\) shows an interactive iCn3D model of the mammalian tactile channel PIEZO2 (6KG7) (long load time)

Figure \(\PageIndex{b}\): Mammalian tactile channel PIEZO2 (6KG7). (Copyright; author via source). Click the image for a popup or use this external link: https://structure.ncbi.nlm.nih.gov/i...4FaL71AL23KiA9 (long load time)

In the Piezo2 channel, charged residues at the interface between the beam and the CTD are required to maintain the channel's normal mechanosensitivity. Moreover, single-channel recordings indicated that a previously unrecognized intrinsically disordered domain adjacent to the beam acts as a cytosolic plug that limits ion permeation, possibly by clogging the inner vestibule in both Piezo1 and Piezo2. Furthermore, by structurally comparing the Piezo1 and Piezo2 channels, Wang et al. found that the Piezo2 channel has additional constriction sites at L2743, F2754, and E2757 that might serve as a transmembrane gate controlled by the cap domain.

Lever-like mechanotransduction mechanism

Based on the unique topological features of the mPiezo1 channel, a lever-like mechanotransduction mechanism to explain its extraordinary mechanosensitivity was proposed (Figure \(\PageIndex{4}\)). In the mPiezo1 channel, the curved blades composed of THUs can act as a mechanosensor, while the beam structure, with the residues Ll1342 and Ll1345 acting as a pivot, can act as a lever-like apparatus. Coupling the distal blades and the central pore through the lever-like apparatus converts mechanical force into a force used for cation conduction.

Figure \(\PageIndex{4}\): Model of the lever-like mechanotransduction model. The curved blades can act as mechanosensors, while the beam structure, with residues Ll1342 and Ll1345 serving as pivots, can function as a lever-like apparatus. Coupling of the distal blades and the central pore through the lever-like apparatus converts mechanical force into cation conduction. A Proposed model of the force-induced gating of Piezo channels. The blue and orange models represent the channel in its closed and open states, respectively. Red dashed lines indicate possible ion-conduction pathways.  Adapted from Ge et al. B A lever-like mechano-gating model in Piezo1. The blue and red dashed arrows indicate input and output forces, respectively.

Because the lever's pivot is positioned closer to the central pore than to the distal blades, the input force is effectively amplified through the lever-like apparatus. Additionally, a large conformational change in the distal blades results in a relatively slight opening of the central pore, allowing cation-selective permeation.

Kinetic properties of Piezo channels

Activation mechanisms of Piezo channels

Normal Piezo channel kinetics can be modeled with three states: open, closed, and inactivated; these states collectively emerge as an important mechanism in Piezo channel function. Studies have proposed that the Piezo1 channel is gated directly by bilayer tension, which can be modified by cytoskeletal proteins and by linkages to the extracellular matrix (ECM). For example, in overhydrated red blood cells (RBCs), Piezo1-mediated Ca²⁺ influx activates K⁺ efflux through the Gardos channel (KCa3.1), leading to water loss and RBC dehydration.

Piezo1 and Piezo2 channels exhibit a three-bladed, propeller-shaped trimeric architecture and can locally deform lipid membranes into a dome-like shape. In addition, changes in the projection area of Piezo channels from closed to open are essential for their mechanosensitivity; this was investigated by calculating the available free energy. Based on these findings, the membrane dome mechanism was proposed and experimentally proved to explain the activation mechanisms of Piezo channels  (Figure \(\PageIndex{5}\)). Essentially, the dome shape created by Piezo channels in their closed conformation acts as a potential energy source for MS gating. Under tension, the lateral membrane flattens the Piezo dome, increasing the energy of the membrane-channel system in proportion to the expansion of the projected dome area. Piezo channels then open due to the relative energy difference. This mechanism can account for the highly sensitive mechanical gating of Piezo channels via a cation-selective pore. Although the membrane-dome mechanism explains the exquisite mechanosensitivity of Piezo channels, it does not account for the shape of the surrounding membrane. Haselwandter et al. proposed the membrane footprint hypothesis, which states that the Piezo1 channel deforms the membrane outside its perimeter, producing a curved membrane footprint that amplifies Piezo1's sensitivity to changes in membrane tension. Nevertheless, further experiments are needed to test and refine these hypotheses.

Figure \(\PageIndex{5}\): Model of the membrane doming mechanisms. Changes in membrane curvature lead to a gating force applied to the Piezo1 channel

Inactivation kinetics of Piezo channels

Various types of mechanical stimulation trigger Piezo channel activation and sequentially elicit an MA current with rapid decay, even during continued stimulation, due to rapid inactivation. Coste et al. first described the voltage-dependent inactivation kinetics of Piezo channels, which were characterized as fast at rather negative membrane potentials and slow at rather positive membrane potentials. Additionally, Piezo1 channel inactivation is relatively slow compared with that of the Piezo2 channel. Several point mutations in Piezo channels have been reported to slow the inactivation process, leading to larger cation fluxes and various human diseases. Given their demonstrated key role in normal channel function, we will next review what is known about the inactivation kinetics of Piezo channels, focusing on the inactivation mechanism.

The available information regarding the structures (residues/domains) and human disease-related point mutations has helped clarify ion channel inactivation mechanisms. Currently, six gain-of-function mutations associated with dehydrated hereditary xerocytosis (DHS) have been found to slow the inactivation rate of Piezo channels (Table \(\PageIndex{1}\)), most of which are clustered at the central core region of the Piezo channel structure. This implies that the pore region, which contains an OH, an IH, an extracellular cap domain, and an intracellular CTD, determines the kinetics of inactivation. Further links between structural domains and inactivation kinetics have been investigated in greater detail. Wu et al. found that the distinct inactivation kinetics of Piezo1 and Piezo2 channels and the characteristic voltage-dependent inactivation appear to be determined by the C-terminal extracellular domain (cap domain). Two potential inactivation gates within the IH and CTD have been considered sufficient for the normal inactivation of the Piezo1 and Piezo2 channels. Recently, three small subdomains within the extracellular cap were shown to confer Piezo channel inactivation individually. These results support the idea that the ion-conducting pore region of Piezo channels is essential for their inactivation properties.

Table \(\PageIndex{2}\): Mutations in Piezo1 and Piezo2 Associated with Human Diseases: Full-size table

Interestingly, a slowly inactivating MS current in mouse embryonic stem cells (mESs) that is dependent on the Piezo1 channel has been described. However, heterologous expression of Piezo1 cDNA from mES cells displays fast inactivation kinetics, indicating that additional regulatory mechanisms other than the amino acid sequence determine the slow kinetics of the Piezo1 channel in mES cells. Recently, sphingomyelinase activity has been revealed to be a crucial determinant of Piezo1 inactivation. Various modulators, such as pH, temperature, divalent ion concentrations, alternative splicing, osmotic swelling, membrane lipid composition, co-expression of other membrane proteins, and G-protein-coupled pathways, have also been reported to regulate the Piezo channel kinetics; however, we still know very little about the relationships among these factors and pivotal structural domains.

Pharmacological modulators of Piezo channels

Despite the relatively recent discovery of Piezos, progress has been made regarding small-molecule modulators of Piezo1. Piezo1 chemical activators, including Yoda1 and Jedi1/2, were able to open Piezo1 ion channels in the absence of mechanical stimulation. Jedi1/2, a novel hydrophilic Piezo1 chemical activator, acts through the peripheral blades and utilizes a peripheral lever-like apparatus consisting of the blades and a beam to gate the central ion-conducting pore, whereas Yoda1 acts as a molecular wedge, facilitating force-induced conformational changes, effectively lowering the channel’s mechanical threshold for activation. However, the reason why Yoda1 does not efficiently activate the Piezo2 channel is unclear. Specific inhibitors of Piezo1 are in their infancy. As nonspecific inhibitors of the ion pore in stretch-activated ion channels, gadolinium and ruthenium red have also been shown to block mouse Piezo1 channels with IC50 values of approximately 5 mM. The commonly used toxin inhibitor of mechanosensitive channels, GsMTx4, also inhibited the Piezo1 channel. Still, it might not bind Piezo1 directly, but rather act via modulating local membrane tension near the channel. Dooku1, an analog of Yoda1 without a stimulatory effect, antagonizes Yoda1-evoked activation of Piezo1 and aortic relaxation.

The function of Piezo channels

Piezo channels are expressed in a wide range of mechanosensitive cells and allow Ca²⁺ influx in response to various external forces, such as fluid flow, pulling, and ultrasonic stimulation. The biological function of Piezo channels was recently investigated in many studies (Figure \(\PageIndex{6}\)). The results of these studies verified the pivotal roles of Piezo channels in mechanotransduction under physiological and pathophysiological conditions. Here, we review the biological function of Piezo channels in various MS tissues and cells.

Figure \(\PageIndex{6}\): Expression and function of Piezo channels. Multiple tissues and cells express Piezo channels, and each of those shown is discussed in this review. Panels a–e demonstrate the vital role of the Piezo1 channel in the CNS, blood vessels, erythrocytes, lungs, gastrointestinal tract, and urinary tract. Panels f–h illustrate the expression of both the Piezo1 channel and Piezo2 channel in articular cartilage, trigeminal ganglia, and dorsal root ganglia. Panel i shows that the Piezo2 channel is expressed in Merkel cells, which are involved in sensing light touch.

Consult the original article for details on the roles of Piezo channels in the systems above.

Summary

(Summary written by Claude, Sonnet 4.6, Anthropic)

Mechanotransduction—the conversion of mechanical stimuli into electrochemical signals—is fundamental to numerous physiological processes including pain sensation, touch perception, vascular tone regulation, and red blood cell volume homeostasis. Among the mechanosensitive ion channels found across organisms from bacteria to mammals, the Piezo family (Piezo1 and Piezo2), discovered in 2010, represents the best-characterized dedicated mechanosensors in mammalian cells.

Piezo channels are structurally unprecedented: each homotrimeric complex assembles from three subunits, each containing 38 transmembrane segments, giving rise to a three-bladed propeller-shaped architecture visible by cryo-EM. The 36 peripheral transmembrane segments (TM1–TM36) organize into nine four-helix transmembrane helical units (THUs) that form curved, clockwise-twisted blade-like structures ideally suited to sense and locally deform lipid bilayer curvature. A 90 nm intracellular beam, running at 30° to the membrane plane, physically bridges the distal blades to the central ion-conducting pore module, which consists of the inner helix (IH), outer helix (OH), C-terminal extracellular domain (CED) forming the trimeric cap, and C-terminal domain (CTD) forming the intracellular vestibule. The central pore contains an extracellular vestibule within the cap, a transmembrane vestibule, and an intracellular vestibule connected in series. Cation selectivity over anions is conferred by the negatively charged DEEED patch (residues 2393–2397) in the extracellular cap opening, while divalent Ca²⁺ selectivity and unitary conductance are determined by acidic residues E2495 and E2496 in the intracellular vestibule. An anchor domain of three helices in an inverted V-shaped structure maintains pore integrity, and an α3 helix links the outer helix to the CTD; several mutations in this region cause severe hereditary disease.

The lever-like mechanotransduction model proposes that curved peripheral blades act as mechanosensors while the intracellular beam—with residues L1342 and L1345 serving as the pivot point—acts as a mechanical lever. Because the pivot is positioned closer to the central pore than to the distal blade tips, small movements at the pivot produce amplified displacements at the blade tips, while conversely, large conformational changes in the distal blades are converted into a relatively slight opening of the central pore, enabling sensitive cation-selective mechanosensing. The membrane dome mechanism complements this model by describing how closed Piezo channels impose a dome-shaped curvature on the local lipid bilayer, storing potential energy; lateral membrane tension flattens the dome, expands the channel's projected area, and drives channel opening. The membrane footprint hypothesis further proposes that Piezo1 deforms the membrane beyond its own perimeter, amplifying tension sensitivity through a curved membrane footprint.

Piezo channels follow a three-state kinetic model (open, closed, inactivated) with voltage-dependent inactivation—fast at hyperpolarized potentials and slow at depolarized potentials—that is structurally determined primarily by the C-terminal extracellular cap domain, the IH, and the CTD. Six gain-of-function mutations in Piezo1 associated with dehydrated hereditary xerocytosis (DHS) slow inactivation, producing excessive Ca²⁺ influx in red blood cells that activates the Gardos channel (KCa3.1), driving K⁺ and water efflux, and causing red cell dehydration and hemolytic anemia. Additional inactivation modulators include sphingomyelinase activity, membrane lipid composition, pH, temperature, and alternative splicing, highlighting the sophisticated regulatory mechanisms governing Piezo channel kinetics.

Pharmacological tools for Piezo research include the chemical activators Yoda1 (which acts as a molecular wedge, lowering the mechanical activation threshold) and Jedi1/2 (which gates Piezo1 via the peripheral blade-lever apparatus), with Dooku1 serving as a Yoda1 antagonist. Nonspecific blockers include gadolinium, ruthenium red, and the spider toxin peptide GsMTx4, which may act by modulating local membrane tension rather than directly occluding the pore. Piezo1 is expressed predominantly in nonsensory mechanically active tissues (lung, bladder, skin, vasculature, red blood cells), while Piezo2 is expressed in sensory tissues, including DRG neurons and Merkel cells, where it mediates light touch and proprioception. Mutations in both channels underlie multiple hereditary diseases, including congenital lymphatic dysplasia, dehydrated hereditary xerocytosis, and muscular atrophy with perinatal respiratory distress, underscoring the critical importance of precisely regulated mechanosensitive ion flux across diverse tissues and physiological contexts.