1. Human V-ATPase a-subunit isoforms bind specifically to distinct phosphoinositide phospholipids.
- Author
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Mitra C, Winkley S, and Kane PM
- Subjects
- Humans, Binding Sites, Endosomes enzymology, Endosomes metabolism, Golgi Apparatus enzymology, Golgi Apparatus metabolism, Hydrogen-Ion Concentration, Lysosomes enzymology, Lysosomes metabolism, Protein Isoforms chemistry, Protein Isoforms metabolism, Saccharomyces cerevisiae enzymology, Saccharomyces cerevisiae metabolism, Substrate Specificity, Protein Domains, Phosphatidylinositol Phosphates metabolism, Protein Subunits chemistry, Protein Subunits metabolism, Vacuolar Proton-Translocating ATPases chemistry, Vacuolar Proton-Translocating ATPases metabolism
- Abstract
Vacuolar H
+ -ATPases (V-ATPases) are highly conserved multisubunit enzymes that maintain the distinct pH of eukaryotic organelles. The integral membrane a-subunit is encoded by tissue- and organelle-specific isoforms, and its cytosolic N-terminal domain (aNT) modulates organelle-specific regulation and targeting of V-ATPases. Organelle membranes have specific phosphatidylinositol phosphate (PIP) lipid enrichment linked to maintenance of organelle pH. In yeast, the aNT domains of the two a-subunit isoforms bind PIP lipids enriched in the organelle membranes where they reside; these interactions affect activity and regulatory properties of the V-ATPases containing each isoform. Humans have four a-subunit isoforms, and we hypothesize that the aNT domains of these isoforms will also bind to specific PIP lipids. The a1 and a2 isoforms of human V-ATPase a-subunits are localized to endolysosomes and Golgi, respectively. We determined that bacterially expressed Hua1NT and Hua2NT bind specifically to endolysosomal PIP lipids PI(3)P and PI(3,5)P2 and Golgi enriched PI(4)P, respectively. Despite the lack of canonical PIP-binding sites, we identified potential binding sites in the HuaNT domains by sequence comparisons and existing subunit structures and models. We found that mutations at a similar location in the distal loops of both HuaNT isoforms compromise binding to their cognate PIP lipids, suggesting that these loops encode PIP specificity of the a-subunit isoforms. These data suggest a mechanism through which PIP lipid binding could stabilize and activate V-ATPases in distinct organelles., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)- Published
- 2023
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