Work

Differential ion selectivity and disease-associated dysfunction of TRPML channels revealed by patient and engineered mutants

Year: 2025

Type: article

Abstract: The endolysosomal TRPML (transient receptor potential mucolipin) channels play key roles in regulating lysosomal trafficking, signaling, and function. While mutations in TRPML1 cause mucolipidosis type IV (MLIV), the functional consequences of many disease-associated mutations remain unclear. In this study, we used live-cell confocal imaging in HeLa cells to comprehensively characterize the subcellular localization and cation (Ca 2+ and Zn 2+ ) permeability of TRPML1-3, ten TRPML1 MLIV patient-derived mutants, and engineered pore mutants. We showed that TRPML1 and TRPML3 permeate both Ca 2+ and Zn 2+ , whereas TRPML2 conducts only Ca 2+ . Subcellular localization analyses revealed that TRPML1 and TRPML2 localize predominantly to lysosomes, while TRPML3 is preferentially localized to the ER. Among the ten patient-derived TRPML1 mutants, nine exhibited severely impaired agonist-mediated Ca 2+ and Zn 2+ permeability, indicating severe functional loss. In contrast, the F408Δ mutant, associated with a milder phenotype, retained partial ion permeability and was the only mutant capable of constitutive Ca 2+ permeation without agonist stimulation. Interestingly, we found that non-functional, lysosome-localized TRPML1 mutants are associated with more severe disease phenotypes than those retained in the ER, suggesting that lysosomal localization of non-functional TRPML1 may have dominant-negative or toxic effects. Finally, through structure-guided mutagenesis, we generated a metal-selective TRPML1 mutant, I468V, that is permeable to Ca 2+ but not to Zn 2+ , providing a new tool for dissecting the distinct physiological roles of Zn 2+ and Ca 2+ in TRPML1-mediated processes. Together, these findings provide new insights into how TRPML1 mutations disrupt subcellular localization, ion permeability, and selectivity, which contribute to the variable clinical spectrum of MLIV.

Source: Journal of Biological Chemistry

DOI: 10.1016/j.jbc.2025.110953