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Expression and Purification of the Human Lipid-sensitive Cation Channel TRPC3 for Structural Determination by Single-particle Cryo-electron Microscopy
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TPC proteins are phosphoinositide- activated sodium-selective ion channels in endosomes and lysosomes

Xiang Wang1, Xiaoli Zhang, Xian-Ping Dong

  • 1Department of Molecular, Cellular, and Developmental Biology, University of Michigan, 3089 Kraus Natural Science Building, 830 North University Avenue, Ann Arbor, MI 48109, USA.

Cell
|October 16, 2012
PubMed

Insights

Mammalian two-pore channels (TPCs) are sodium-selective, not calcium-selective, and are activated by PI(3,5)P(2), not NAADP. This discovery redefines the role of TPCs in regulating endolysosomal function and ion transport.

Area of Science:

  • Cell Biology
  • Ion Channel Physiology
  • Molecular Neuroscience

Background:

  • Mammalian two-pore channel proteins (TPC1, TPCN1, TPC2, TPCN2) are located in endosomes and lysosomes.
  • They were previously thought to mediate calcium release triggered by nicotinic acid adenine dinucleotide phosphate (NAADP).

Purpose of the Study:

  • To directly investigate the ion selectivity and gating mechanisms of mammalian two-pore channels (TPCs).
  • To clarify the primary ion transported in endolysosomes and the role of TPCs in organelle function.

Main Methods:

  • Direct electrophysiological recordings of TPCs in endolysosomes.
  • Experiments utilized wild-type and TPC double-knockout mouse models.

Main Results:

  • TPCs were found to be sodium-selective channels, not calcium-selective.
  • Activation of TPCs was dependent on PI(3,5)P(2), and independent of NAADP.
  • Sodium (Na+) was identified as the primary ion in endolysosomes, challenging the prevailing assumption of potassium (K+).

Conclusions:

  • Mammalian TPCs function as sodium-selective channels regulated by PI(3,5)P(2).
  • These findings revise our understanding of endolysosomal ion transport and membrane potential regulation.
  • The results provide a new basis for understanding the role of PI(3,5)P(2) in organelle fusion.

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