Human V-ATPase a-subunit isoforms bind specifically to distinct phosphoinositide phospholipids.

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Vacuolar H+-ATPases (V-ATPases) are crucial for maintaining organelle pH in eukaryotes.
• The V-ATPase a-subunit's N-terminal domain (aNT) influences organelle-specific V-ATPase regulation and targeting.
• Organelle membranes exhibit specific phosphatidylinositol phosphate (PIP) lipid compositions.

Purpose of the Study:

• To investigate if human V-ATPase aNT domains bind specific PIP lipids, analogous to yeast.
• To determine the PIP lipid binding specificities of human V-ATPase a1 and a2 isoforms.
• To identify potential PIP-binding sites within the human aNT domains.

Main Methods:

• Bacterial expression of human V-ATPase a1 and a2 N-terminal domains (Hua1NT, Hua2NT).
• PIP lipid binding assays to determine specificity for endolysosomal and Golgi lipids.
• Sequence comparisons and structural analysis to identify potential binding sites.
• Site-directed mutagenesis to probe the function of identified binding regions.

Main Results:

• Hua1NT specifically bound to endolysosomal PIP lipids PI(3)P and PI(3,5)P2.
• Hua2NT specifically bound to Golgi-enriched PIP lipid PI(4)P.
• Mutations in distal loops of HuaNT domains impaired cognate PIP lipid binding, indicating these regions confer specificity.

Conclusions:

• Human V-ATPase aNT domains exhibit specific PIP lipid binding preferences.
• PIP lipid interactions likely play a role in the organelle-specific localization, stability, and activation of V-ATPases.
• Distal loops of the aNT domain are critical for mediating PIP lipid specificity.