On the Structure and Mechanism of Two-Pore Channels

In eukaryotes, two-pore channels (TPC1-3) comprise a family of ion channels that regulate the conductance of Na + and Ca 2+ ions across cellular membranes. TPC1-3 form endolysosomal channels, but TPC3 can also function in the plasma membrane. TPC1/3 are voltage-gated channels, but TPC2 opens in response to binding endolysosome-specific lipid phosphatidylinositol-3,5-diphosphate (PI(3,5)P 2 ). Filoviruses, such as Ebola, exploit TPC-mediated ion release as a means of escape from the endolysosome during infection. Antagonists that block TPC1/2 channel conductance abrogate filoviral infections. TPC1/2 form complexes with the mechanistic target of rapamycin complex 1 (mTORC1) at the endolysosomal surface that couple cellular metabolic state and cytosolic nutrient concentrations to the control of membrane potential and pH. We determined the X-ray structure of TPC1 from Arabidopsis thaliana (AtTPC1) to 2.87Å resolution–one of the two first reports of a TPC channel structure. Here we summarize these findings and the implications that the structure may have for understanding endolysosomal control mechanisms and their role in human health. Abbreviations mTORC1 Mechanistic target of rapamycin complex 1 TPC Two-pore channel PI(3,5)P 2 Phosphatidylinositol-3,5-diphosphate AtTPC1 Arabidopsis thaliana TPC1 NED19 Trans-Ned-19 VSD Voltage-sensing domain P1 Pore domain in S5-S6 P2 Pore domain in S11-S12 Ca v Voltage-gated calcium channel Na v Voltage-gated sodium channel K v Voltage-gated potassium channel NTD N-terminal domain CTD C-terminal domain EF EF-hand domain NAADP Nicotinic acid adenine dinucleotide phosphate PI(4,5)P 2 Phosphatidylinositol-4,5-diphosphate DHP Dihydropyridine PAA Phenylalkylamine BTZ Benzothiazepine Ca a 2+ Activating Ca 2+ -ion Ca i 2+ Inhibitory Ca 2+ -ion fou2 Fatty acid oxygenation up-regulated 2 SLC38a9 Sodium-coupled neutral amino acid transporter 9 NPC1 Niemann-Pick C1 PKA Protein kinase A PKC Protein kinase C PKG Protein kinase G H + ATPase - Proton Pump 32 P – Phosphorus-32