pH-dependent regulation in SLC38A9

Area of Science:

• Cellular biology
• Biochemistry
• Molecular mechanisms

Background:

• Cells require strict metabolic regulation for environmental adaptation.
• The mechanistic target of rapamycin complex 1 (mTORC1) pathway regulates cell growth and metabolism, sensing nutrient availability, particularly amino acids.
• Lysosomes are crucial for nutrient recycling and maintaining amino acid homeostasis.

Purpose of the Study:

• To investigate the pH-dependent regulation of the lysosomal amino acid transporter SLC38A9.
• To identify the specific residues involved in pH sensing and their mechanism of action.
• To elucidate the structural basis for pH-induced activation of SLC38A9.

Main Methods:

• Biochemical assays to measure arginine uptake by SLC38A9.
• Site-directed mutagenesis of the histidine residue His544.
• Determination of SLC38A9 crystal structures at different pH values.
• Comparative structural analysis to model pH-induced conformational changes.

Main Results:

• Arginine transport by SLC38A9 is significantly influenced by pH.
• The histidine residue His544 was identified as the critical pH sensor, mediating pH-dependent transport.
• Mutating His544 abolished pH sensitivity without affecting basal transport activity.
• Structural comparison revealed distinct conformations of SLC38A9 at high and low pH, supporting a model of pH-induced activation.

Conclusions:

• SLC38A9 activity is regulated by the lysosomal pH.
• His544 plays a key role in sensing pH changes and modulating transporter function.
• These findings reveal a novel mechanism of lysosomal transporter regulation and its impact on mTORC1 signaling.