Molecular principles of Piezo1 activation by increased membrane tension

Piezo1 is a mechanosensitive channel involved in many cellular functions and responsible for sensing shear-stress and pressure forces in cells. Piezo1 plays a critical role in the circulatory system and tissue development. Mutations on Piezo1 are linked to human diseases such as lymphedema or hematological disorders such as hemolytic anaemia and resistance to malaria. Hypotheses for Piezo1 gating include the force-from-lipids principle that suggests that Piezo1 senses mechanical forces through the bilayer and a direct involvement of the cytoskeleton as well as the extracellular matrix in Piezo1 activation. However, the molecular and structural changes underpinning the Piezo1 gating mechanism and how the channel senses forces in the membrane remain unknown. Here we reveal the activation mechanism of Piezo1 and the structural rearrangements that occur when Piezo1 moves from a closed to an open state when mechanical tension is applied to the cell membrane. Our results show that the curved shape of Piezo1 is stable in a native-like model membrane without tension creating a membrane indentation with a trilobed topology. Upon stretching Piezo1 adapts to the stretched bilayer by flattening and expansion of its blade region. In our simulations Piezo1 expands up to a planar circular area of ~680 nm2 comparable with previous structural data and hypotheses. Piezo1 flattening and expansion results in changes in the beam helix tilt angle. These movements result in the tilting and lateral movement of the pore lining TM37 and TM38 helices. This leads to the opening of the channel and to the movement of lipids that occupy Piezo1 pore region outside of this region, revealing for the first time the structural changes that happen during Piezo1 mechanical activation. The changes in the blade region are transmitted to helices TM37 and 38 via hydrophobic interactions and by interactions of neighbouring subunits via the elbow region. The flat structure of Piezo1 identified in this study exposes the C-terminal extracellular domain (CED) that in the closed state is hidden in the membrane and presumably from shear stress. Our results provide new structural data for different states of Piezo1 and suggest the molecular principles by which mechanical force opens the Piezo1 channel, thus coupling force to physiological effect via ion permeation.