Convergent activation of Ca <sup>2+</sup> permeability in two-pore channel 2 through distinct molecular routes
Ryo� Saito, Qianru Mu, Yu Yuan, Marcos Rubio‐Alarcón, Maria Eznarriaga, Pingwei Zhao, Gihan S. Gunaratne, Sushil Kumar, Marco Keller, Franz Bracher, Christian Grimm, Eugen Brailoiu, Jonathan S. Marchant, Taufiq Rahman, Sandip Patel
Abstract
TPC2 is a pathophysiologically relevant lysosomal ion channel that is activated directly by the phosphoinositide PI(3,5)P 2 and indirectly by the calcium ion (Ca 2+ )–mobilizing molecule NAADP through accessory proteins that associate with the channel. TPC2 toggles between PI(3,5)P 2 -induced, sodium ion (Na + )–selective and NAADP-induced, Ca 2+ –permeable states in response to these cues. To address the molecular basis of polymodal gating and ion-selectivity switching, we investigated the mechanism by which NAADP and its synthetic functional agonist, TPC2-A1-N, induced Ca 2+ release through TPC2 in human cells. Whereas NAADP required the NAADP-binding proteins JPT2 and LSM12 to evoke endogenous calcium ion signals, TPC2-A1-N did not. Residues in TPC2 that bind to PI(3,5)P 2 were required for channel activation by NAADP but not for activation by TPC2-A1-N. The cryptic voltage-sensing region of TPC2 was required for the actions of TPC2-A1-N and PI(3,5)P 2 but not for those of NAADP. These data mechanistically distinguish natural and synthetic agonist action at TPC2 despite convergent effects on Ca 2+ permeability and delineate a route for pharmacologically correcting impaired NAADP-evoked Ca 2+ signals.