TRPML2 in distinct states reveals the activation and modulation principles of the TRPML family.

TRPML2 activity is critical for endolysosomal integrity and chemokine secretion, and can be modulated by various ligands. Interestingly, two ML-SI3 isomers regulate TRPML2 oppositely. The molecular mechanism underlying this unique isomeric preference as well as the TRPML2 agonistic mechanism remains unknown.

Lysosomal TMEM165 controls cellular ion homeostasis and survival by mediating lysosomal Ca import and H efflux.

The proper function of lysosomes depends on their ability to store and release calcium. While several lysosomal calcium release channels have been described, how lysosomes replenish their calcium stores in placental mammals has not been determined. Using genetic depletion and overexpression techniques combined with electrophysiology and visualization of subcellular ion concentrations and their fluxes across the lysosomal membrane, we show here that TMEM165 imports calcium to the lysosomal lumen and mediates calcium-induced lysosomal proton leakage.

TPCs: FROM PLANT TO HUMAN.

In 2005, the two-pore channel TPC1 channel was identified as a vacuolar Ca-release channel. In 2009, three independent groups published studies on mammalian TPCs as nicotinic acid adenine dinucleotide phosphate (NAADP)-activated endolysosomal Ca release channels, results that were eventually challenged by two other groups, claiming mammalian TPCs to be phosphatidylinositol-3,5-bisphosphate [PI(3,5)P2]-activated Na channels. By now this dispute seems to have been largely reconciled.

Structural basis for inhibition of the lysosomal two-pore channel TPC2 by a small molecule antagonist.

Two pore channels are lysosomal cation channels with crucial roles in tumor angiogenesis and viral release from endosomes. Inhibition of the two-pore channel 2 (TPC2) has emerged as potential therapeutic strategy for the treatment of cancers and viral infections, including Ebola and COVID-19. Here, we demonstrate that antagonist SG-094, a synthetic analog of the Chinese alkaloid medicine tetrandrine with increased potency and reduced toxicity, induces asymmetrical structural changes leading to a single binding pocket at only one intersubunit interface within the asymmetrical dimer.

Sugar beet PMT5a and STP13 carriers suitable for proton-driven plasma membrane sucrose and glucose import in taproots.

Sugar beet (Beta vulgaris) is the major sugar-producing crop in Europe and Northern America, as the taproot stores sucrose at a concentration of around 20%. Genome sequence analysis together with biochemical and electrophysiological approaches led to the identification and characterization of the TST sucrose transporter driving vacuolar sugar accumulation in the taproot. However, the sugar transporters mediating sucrose uptake across the plasma membrane of taproot parenchyma cells remained unknown.

Coordinating activation of endo-lysosomal two-pore channels and TRP mucolipins.

Two-pore channels and TRP mucolipins are ubiquitous endo-lysosomal cation channels of pathophysiological relevance. Both are Ca-permeable and regulated by phosphoinositides, principally PI(3,5)P. Accumulating evidence has uncovered synergistic channel activation by PI(3,5)P and endogenous metabolites such as the Ca mobilizing messenger NAADP, synthetic agonists including approved drugs and physical cues such as voltage and osmotic pressure.

OCaR1 endows exocytic vesicles with autoregulatory competence by preventing uncontrolled Ca2+ release, exocytosis, and pancreatic tissue damage.

Regulated exocytosis is initiated by increased Ca2+ concentrations in close spatial proximity to secretory granules, which is effectively prevented when the cell is at rest. Here we showed that exocytosis of zymogen granules in acinar cells was driven by Ca2+ directly released from acidic Ca2+ stores including secretory granules through NAADP-activated two-pore channels (TPCs). We identified OCaR1 (encoded by Tmem63a) as an organellar Ca2+ regulator protein integral to the membrane of secretory granules that controlled Ca2+ release via inhibition of TPC1 and TPC2 currents.

SV channel VfTPC1 is a hyperexcitable variant of plant vacuole Two Pore Channels.

To fire action-potential-like electrical signals, the vacuole membrane requires the two-pore channel TPC1, formerly called SV channel. The TPC1/SV channel functions as a depolarization-stimulated, non-selective cation channel that is inhibited by luminal Ca. In our search for species-dependent functional TPC1 channel variants with different luminal Ca sensitivity, we found in total three acidic residues present in Ca sensor sites 2 and 3 of the Ca-sensitive AtTPC1 channel from that were neutral in its ortholog and also in those of many other Fabaceae.

TRPML3/BK complex promotes autophagy and bacterial clearance by providing a positive feedback regulation of mTOR via PI3P.

TRPML3 is a Ca/Na release channel residing in both phagophores and endolysosomal membranes. It is activated by PI3P and PI3,5P2. Its activity can be enhanced by high luminal pH and by replacing luminal Na with K.

PI(3,5)P and NAADP: Team players or lone warriors? - New insights into TPC activation modes.

NAADP (nicotinic acid adenine dinucleotide phosphate) is a second messenger, releasing Ca from acidic calcium stores such as endosomes and lysosomes. PI(3,5)P (phosphatidylinositol 3,5-bisphosphate) is a phospho-inositide, residing on endolysosomal membranes and likewise releasing Ca from endosomes and lysosomes. Both compounds have been shown to activate endolysosomal two-pore channels (TPCs) in mammalian cells.

Neurodegenerative Lysosomal Storage Disorders: TPC2 Comes to the Rescue!

Lysosomal storage diseases (LSDs) resulting from inherited gene mutations constitute a family of disorders that disturb lysosomal degradative function leading to abnormal storage of macromolecular substrates. In most LSDs, central nervous system (CNS) involvement is common and leads to the progressive appearance of neurodegeneration and early death. A growing amount of evidence suggests that ion channels in the endolysosomal system play a crucial role in the pathology of neurodegenerative LSDs.

Electrophysiology of Endolysosomal Two-Pore Channels: A Current Account.

Two-pore channels TPC1 and TPC2 are ubiquitously expressed pathophysiologically relevant proteins that reside on endolysosomal vesicles. Here, we review the electrophysiology of these channels. Direct macroscopic recordings of recombinant TPCs expressed in enlarged lysosomes in mammalian cells or vacuoles in plants and yeast demonstrate gating by the Ca-mobilizing messenger NAADP and/or the lipid PI(3,5)P.

TPC2 rescues lysosomal storage in mucolipidosis type IV, Niemann-Pick type C1, and Batten disease.

Lysosomes are cell organelles that degrade macromolecules to recycle their components. If lysosomal degradative function is impaired, e.g.

Segregated cation flux by TPC2 biases Ca signaling through lysosomes.

Two-pore channels are endo-lysosomal cation channels with malleable selectivity filters that drive endocytic ion flux and membrane traffic. Here we show that TPC2 can differentially regulate its cation permeability when co-activated by its endogenous ligands, NAADP and PI(3,5)P. Whereas NAADP rendered the channel Ca-permeable and PI(3,5)P rendered the channel Na-selective, a combination of the two increased Ca but not Na flux.

Evolutionary Aspects of TRPMLs and TPCs.

Transient receptor potential (TRP) or transient receptor potential channels are a highly diverse family of mostly non-selective cation channels. In the mammalian genome, 28 members can be identified, most of them being expressed predominantly in the plasma membrane with the exception of the mucolipins or TRPMLs which are expressed in the endo-lysosomal system. In mammalian organisms, TRPMLs have been associated with a number of critical endo-lysosomal functions such as autophagy, endo-lysosomal fusion/fission and trafficking, lysosomal exocytosis, pH regulation, or lysosomal motility and positioning.

Voltage-dependent gating of SV channel TPC1 confers vacuole excitability.

In contrast to the plasma membrane, the vacuole membrane has not yet been associated with electrical excitation of plants. Here, we show that mesophyll vacuoles from Arabidopsis sense and control the membrane potential essentially via the K-permeable TPC1 and TPK channels. Electrical stimuli elicit transient depolarization of the vacuole membrane that can last for seconds.

Control of basal jasmonate signalling and defence through modulation of intracellular cation flux capacity.

Unknown mechanisms tightly regulate the basal activity of the wound-inducible defence mediator jasmonate (JA) in undamaged tissues. However, the Arabidopsis fatty acid oxygenation upregulated2 (fou2) mutant in vacuolar two-pore channel 1 (TPC1 ) displays high JA pathway activity in undamaged leaves. This mutant was used to explore mechanisms controlling basal JA pathway regulation.