Allosteric switching of Ca2+ permeability in the lysosomal ion channel TPC2 underpins biased agonist activation

EMBO J. 2026 Aug 7. doi: 10.1038/s44318-026-00882-1. Online ahead of print.

ABSTRACT

Ion channels possess selectivity filters that are hardwired to ensure the selective passage of ions. Lysosomal two-pore channels are unusual as they are able to switch their cation selectivity in an agonist-specific manner, allowing differential control of organellar activity. TPC2 is permeable to Ca²⁺ when activated by the calcium-mobilizing messenger NAADP, but largely Na⁺-selective when activated by the signaling lipid PI(3,5)P₂. Co-stimulation increases Ca²⁺ but not Na⁺ permeability; however, the molecular basis for these specificity switches is not well understood. Here we show that mutation of TPC2 residues within the distal cytosolic linker, which connects the first voltage-sensing-like domain to the pore, rendered TPC2 largely unable to discriminate its agonists and highly calcium-permeable, even in the presence of PI(3,5)P₂. This mutation induced a co-activated-like state by disrupting a network of residues that connects the linker to the activation gate. Such deregulated agonist action increased lysosomal Ca²⁺ flux and compromised locomotion and viability when expressed in C. elegans. A proximal disease-linked mutation perturbed agonist action in a similar way both in vitro and in vivo. Biased signaling through TPC2 thus proceeds through molecular determinants that are remote from the selectivity filter, affecting Ca²⁺ permeability, endo-lysosomal integrity and disease.

PMID:42567924 | DOI:10.1038/s44318-026-00882-1