# Molecular physiology of TRPML channels

> **NIH NIH R01** · COLUMBIA UNIV NEW YORK MORNINGSIDE · 2021 · $362,641

## Abstract

Project Summary
The endolysosomal system is essential for cell signaling and physiology. The functions of endocytic vesicles
are regulated by a variety of ion channels, including the mucolipin subfamily of transient receptor potential
(TRPML) channels, which are localized primarily in endosomes and lysosomes. These channels conduct Ca2+
and Na+ currents from the vesicle lumen to the cytoplasm and are critically involved in membrane trafficking,
exocytosis and autophagy. Mutations in TRPML1 cause mucolipidosis type IV (ML IV), a severe lysosomal
storage disorder, and mutations in TRPML3 cause deafness and pigmentation defects in mice, underscoring
the crucial physiological importance of these channels. The activities of TRPML channels are strongly
regulated by endogenous factors such as PIP2, pH, Na+ and Ca2+. The complex regulation in turn controls the
physiological functions of these channels. The objective of this project is to elucidate the molecular
mechanisms of regulation of TRPML3 by these physiological factors. TRPML3 is regulated by both common
and unique mechanisms. Like other TRPMLs, TRPML3 is activated by PI(3, 5)P2 and suppressed by PI(4,
5)P2. However, it is uniquely inhibited by luminal low pH and Na+. This inhibition presumably keeps lysosomal
TRPML3 inactive under physiological conditions. Neutralization or damage of lysosomes likely relieves this
inhibition and activates TRPML3. We have recently solved cryo-EM structures of full length human TRPML3 in
the closed, open and low-pH-inhibited states. These structures reveal a number of unique structural features
and suggest new allosteric regulatory mechanisms. We have also uncovered a novel ‘Inhibition Memory’ that
depends on Na+ and amino acid H283. We will build on these exciting findings and determine the structural
elements and conformational changes underlying the regulation of TRPML3 by low pH, Na+, PI(3, 5)P2 and
PI(4, 5)P2. We will carry out structure-guided mutagenesis studies to test the hypothesis that a luminal pore-
loop and H283 are pH sensors and that transmembrane segments S1 and S2 act as allosteric transducers that
convert low pH-, Na+-, and PIP2-induced local conformational changes to global conformational changes that
either enhance or inhibit channel activity. We will obtain cryo-EM structures of WT and H283A mutant channels
in complex with membrane lipids at different pH and with different alkali ions and of WT channels in complex
with PI(3, 5)P2 or PI(4, 5)P2 at different pH and Na+ concentrations. These studies will yield rich and deep
mechanistic insights into TRPML3 channel regulation and provide new knowledge for the development of
therapeutic strategies for ML IV and other endocytic vesicle-related diseases.

## Key facts

- **NIH application ID:** 10241344
- **Project number:** 5R01GM085234-11
- **Recipient organization:** COLUMBIA UNIV NEW YORK MORNINGSIDE
- **Principal Investigator:** Jian Yang
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $362,641
- **Award type:** 5
- **Project period:** 2009-05-01 → 2023-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10241344

## Citation

> US National Institutes of Health, RePORTER application 10241344, Molecular physiology of TRPML channels (5R01GM085234-11). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10241344. Licensed CC0.

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