On the Structure and Mechanism of Two-Pore Channels

Abstract In eukaryotes, two-pore channels (TPC1-3) comprise a family of ion channels that regulate the conductance of Na+ and Ca2+ 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)P2). 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 2.87? 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. AbbreviationsmTORC1Mechanistic target of rapamycin complex 1TPCTwo-pore channelPI(3,5)P2Phosphatidylinositol-3,5-diphosphateAtTPC1Arabidopsis thaliana TPC1NED19Trans-Ned-19VSDVoltage-sensing domainP1Pore domain in S5-S6P2Pore domain in S11-S12CavVoltage-gated calcium channelNavVoltage-gated sodium channelKvVoltage-gated potassium channelNTDN-terminal domainCTDC-terminal domainEFEF-hand domainNAADPNicotinic acid adenine dinucleotide phosphatePI(4,5)P2Phosphatidylinositol-4,5-diphosphateDHPDihydropyridinePAAPhenylalkylamineBTZBenzothiazepineCaa2+Activating Ca2+-ionCai2+Inhibitory Ca2+-ionfou2Fatty acid oxygenation up-regulated 2SLC38a9Sodium-coupled neutral amino acid transporter 9NPC1Niemann-Pick C1PKAProtein kinase APKCProtein kinase CPKGProtein kinase GH+ATPase - Proton Pump32P– Phosphorus-32