Structural mechanisms of phospholipid activation of the human TPC2 channel
- Elife. 2019 Mar 12;8:e45222. doi: 10.7554/eLife.45222.
- 1. Department of Physiology, University of Texas Southwestern Medical Center, Dallas, United States.
- 2. Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.
- 3. Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, United States.
- 4. Department of Biophysics, Zhejiang University School of Medicine, Hangzhou, China.
- 5. Department of Pathology of Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, China.
- 6. Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, United States.
Mammalian two-pore channels (TPCs) regulate the physiological functions of the endolysosome. Here we present cryo-EM structures of human TPC2 (HsTPC2), a phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2)-activated, Na+ selective channel, in the ligand-bound and apo states. The apo structure captures the closed conformation, while the ligand-bound form features the channel in both open and closed conformations. Combined with functional analysis, these structures provide insights into the mechanism of PI(3,5)P2-regulated gating of TPC2, which is distinct from that of TPC1. Specifically, the endolysosome-specific PI(3,5)P2 binds at the first 6-TM and activates the channel - independently of the membrane potential - by inducing a structural change at the pore-lining inner helix (IS6), which forms a continuous helix in the open state but breaks into two segments at Gly317 in the closed state. Additionally, structural comparison to the voltage-dependent TPC1 structure allowed us to identify Ile551 as being responsible for the loss of voltage dependence in TPC2.