Tethering Piezo channels to the actin cytoskeleton for mechanogating via the cadherin-ß-catenin mechanotransduction complex.

The mechanically activated Piezo channel plays a versatile role in conferring mechanosensitivity to various cell types. However, how it incorporates its intrinsic mechanosensitivity and cellular components to effectively sense long-range mechanical perturbation across a cell remains elusive. Here we show that Piezo channels are biochemically and functionally tethered to the actin cytoskeleton via the cadherin-ß-catenin mechanotransduction complex, whose perturbation significantly impairs Piezo-mediated responses. Mechanistically, the adhesive extracellular domain of E-cadherin interacts with the cap domain of Piezo1, which controls the transmembrane gate, while its cytosolic tail might interact with the cytosolic domains of Piezo1, which are in close proximity to its intracellular gates, allowing a direct focus of adhesion-cytoskeleton-transmitted force for gating. Specific disruption of the intermolecular interactions prevents cytoskeleton-dependent gating of Piezo1. Thus, we propose a force-from-filament model to complement the previously suggested force-from-lipids model for mechanogating of Piezo channels, enabling them to serve as versatile and tunable mechanotransducers.

Molecular basis for allosteric regulation of the type 2 ryanodine receptor channel gating by key modulators.

The type 2 ryanodine receptor (RyR2) is responsible for releasing Ca2+ from the sarcoplasmic reticulum of cardiomyocytes, subsequently leading to muscle contraction. Here, we report 4 cryo-electron microscopy (cryo-EM) structures of porcine RyR2 bound to distinct modulators that, together with our published structures, provide mechanistic insight into RyR2 regulation. Ca2+ alone induces a contraction of the central domain that facilitates the dilation of the S6 bundle but is insufficient to open the pore. The small-molecule agonist PCB95 helps Ca2+ to overcome the barrier for opening. FKBP12.6 induces a relaxation of the central domain that decouples it from the S6 bundle, stabilizing RyR2 in a closed state even in the presence of Ca2+ and PCB95. Although the channel is open when PCB95 is replaced by caffeine and adenosine 5'-triphosphate (ATP), neither of the modulators alone can sufficiently counter the antagonistic effect to open the channel. Our study marks an important step toward mechanistic understanding of the sophisticated regulation of this key channel whose aberrant activity engenders life-threatening cardiac disorders.

Modulation of cardiac ryanodine receptor 2 by calmodulin.

The high-conductance intracellular calcium (Ca2+) channel RyR2 is essential for the coupling of excitation and contraction in cardiac muscle. Among various modulators, calmodulin (CaM) regulates RyR2 in a Ca2+-dependent manner. Here we reveal the regulatory mechanism by which porcine RyR2 is modulated by human CaM through the structural determination of RyR2 under eight conditions. Apo-CaM and Ca2+-CaM bind to distinct but overlapping sites in an elongated cleft formed by the handle, helical and central domains. The shift in CaM-binding sites on RyR2 is controlled by Ca2+ binding to CaM, rather than to RyR2. Ca2+-CaM induces rotations and intradomain shifts of individual central domains, resulting in pore closure of the PCB95 and Ca2+-activated channel. By contrast, the pore of the ATP, caffeine and Ca2+-activated channel remains open in the presence of Ca2+-CaM, which suggests that Ca2+-CaM is one of the many competing modulators of RyR2 gating.

Structure of the human plasma membrane Ca2+-ATPase 1 in complex with its obligatory subunit neuroplastin.

Plasma membrane Ca2+-ATPases (PMCAs) are key regulators of global Ca2+ homeostasis and local intracellular Ca2+ dynamics. Recently, Neuroplastin (NPTN) and basigin were identified as previously unrecognized obligatory subunits of PMCAs that dramatically increase the efficiency of PMCA-mediated Ca2+ clearance. Here, we report the cryo-EM structure of human PMCA1 (hPMCA1) in complex with NPTN at a resolution of 4.1 Å for the overall structure and 3.9 Å for the transmembrane domain. The single transmembrane helix of NPTN interacts with the TM8-9-linker and TM10 of hPMCA1. The subunits are required for the hPMCA1 functional activity. The NPTN-bound hPMCA1 closely resembles the E1-Mg2+ structure of endo(sarco)plasmic reticulum Ca2+ ATPase and the Ca2+ site is exposed through a large open cytoplasmic pathway. This structure provides insight into how the subunits bind to the PMCAs and serves as an important basis for understanding the functional mechanisms of this essential calcium pump family.