Structural basis for PtdInsP₂-mediated human TRPML1 regulation

Area of Science:

• Cell Biology
• Biochemistry
• Structural Biology

Background:

• Transient receptor potential mucolipin 1 (TRPML1) is a lysosomal ion channel crucial for maintaining lysosomal pH and calcium homeostasis.
• TRPML1 activity is modulated by small molecules and lipids, impacting lysosomal function.
• Specific lipids, phosphatidylinositol-3,5-bisphosphate (PtdIns(3,5)P2) and phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2), play regulatory roles in TRPML1-mediated calcium release.

Purpose of the Study:

• To determine the structures of human TRPML1 in complex with regulatory lipids and a synthetic agonist.
• To elucidate the molecular mechanisms by which lipids allosterically regulate TRPML1 channel activity.
• To identify the unique lipid-binding site within the TRPML1 channel.

Main Methods:

• X-ray crystallography was used to obtain high-resolution structures of human TRPML1.
• Electrophysiological characterizations were performed to assess TRPML1 channel function.
• Biochemical analyses were employed to study lipid-protein interactions.

Main Results:

• The structures revealed a novel lipid-binding site on TRPML1, involving extended helices S1, S2, and S3.
• PtdIns(3,5)P2 binds to TRPML1 and, through interactions with Y355 and R403, allosterically activates the channel by moving the S4-S5 linker.
• PtdIns(4,5)P2 binds to TRPML1 and inhibits calcium release, while PtdIns(3,5)P2 and the agonist ML-SA1 exhibit cooperative activation.

Conclusions:

• The study provides the first structural insights into how lipids regulate TRPML1 channel activity.
• A unique allosteric lipid-binding site was identified, explaining the mechanism of lipid-mediated channel modulation.
• These findings offer a molecular basis for understanding TRP channel regulation by lipids and potential therapeutic targeting.