A Broad Response to Intracellular Long-Chain Polyphosphate in Human Cells

2021

BioEssays

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Polyphosphate (polyP) is a ubiquitous biomolecule thought to be present in all cells on Earth. PolyP is deceivingly simple, consisting of repeated units of inorganic phosphates polymerized in long energy‐rich chains. PolyP is involved in diverse functions in mammalian systems—from cell signaling to blood clotting. One exciting avenue of research is a new nonenzymatic post‐translational modification, termed lysine polyphosphorylation, wherein polyP chains are covalently attached to lysine residues of target proteins. While the modification was first characterized in budding yeast, recent work has now identified the first human targets. There is significant promise in this area of biomedical research, but a number of technical issues and knowledge gaps present challenges to rapid progress. In this review, the current state of the field is summarized and existing roadblocks related to the study of lysine polyphosphorylation in higher eukaryotes are introduced. It is discussed how limited methods to identify targets of polyphosphorylation are further impacted by low concentration, unknown regulatory enzymes, and sequestration of polyP into compartments in mammalian systems. Furthermore, suggestions on how these obstacles could be addressed or what their physiological relevance may be within mammalian cells are presented.

Section: Promises and Challengesmentioning

confidence: 99%

Section: Promises and Challengesmentioning

confidence: 99%

Section: Promises and Challengesmentioning

confidence: 99%

See 1 more Smart Citation

The promises of lysine polyphosphorylation as a regulatory modification in mammals are tempered by conceptual and technical challenges

Baijal

2021

BioEssays

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“…Polyphosphate Extractions: Polyphosphate was extracted from yeast pellets containing 8-12 OD600 units using an adapted protocol from Bru et al 2016 7,69 . Cells were resuspended in 400 µL of cold LETS buffer (see buffer recipes section).…”

Section: Apl5 K-r Mutagenesismentioning

confidence: 99%

“…PolyP chains are variable in size, ranging from 3-1000s of units in length, and are linked together via high-energy phosphoanhydride bonds 1 . While once dismissed as 'molecular fossils', recent work suggests that polyP plays critical roles in diverse processes across both prokaryotic and eukaryotic organisms including bacterial virulence, infection control, blood coagulation, protein folding, and diverse aspects of cell signaling [2][3][4][5][6][7] . As such, polyP chains have gained significant interest as a potential target for therapeutics in a wide variety of pathologies.…”

Section: Introductionmentioning

confidence: 99%

Vtc5 is localized to the vacuole membrane by the conserved AP-3 complex to regulate polyphosphate synthesis in budding yeast

Bentley‐DeSousa

2021

Preprint

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Polyphosphates (polyP) are energy-rich polymers of inorganic phosphates assembled into chains ranging from 3-1000s of residues in length. They are thought to exist in all cells on earth and play roles in an eclectic mix of functions ranging from phosphate homeostasis to cell signaling, infection control, and blood clotting. In the budding yeast Saccharomyces cerevisiae, polyP chains are synthesized by the vacuole-bound VTC complex, which synthesizes polyP while simultaneously translocating it into the vacuole lumen where it is stored at high concentrations. VTC's activity is promoted by an accessory subunit called Vtc5. In this work, we find that the conserved AP-3 complex is required for proper Vtc5 localization to the vacuole membrane. In human cells, previous work has demonstrated that mutation of AP-3 subunits gives rise to Hermansky-Pudlak Syndrome, a rare disease with molecular phenotypes that include decreased polyP accumulation in platelet dense granules. In yeast AP-3 mutants, we find that Vtc5 is rerouted to the vacuole lumen by the ESCRT complex, where it is degraded by the vacuolar protease Pep4. Cells lacking functional AP-3 have decreased levels of polyP, demonstrating that membrane localization of Vtc5 is required for its VTC stimulatory activity in vivo. Our work provides insight into the molecular trafficking of a critical regulator of polyP metabolism in yeast. We speculate that AP-3 may also be responsible for the delivery of polyP regulatory proteins to platelet dense granules in higher eukaryotes.

The emerging landscape of eukaryotic polyphosphatases

McCarthy

2023

FEBS Letters

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Polyphosphate (polyP) is a conserved polymer of inorganic phosphate residues that can reach thousands of moieties in length. PolyP has been implicated in cellular functions ranging from energy and phosphate homeostasis to cell signalling in eukaryotes from yeast to humans. Despite the interest in the role of polyP as a signalling molecule, the spatiotemporal regulation of polyP itself remains poorly understood. This knowledge gap limits our ability to understand how polyP impacts the physiology of normal and diseased cells and how this might be exploited in a therapeutic context. Polyphosphatases, enzymes that degrade polyP to generate shorter chains and free inorganic phosphate are ideally positioned to mediate polyP dynamics. However, little is known about how the activities of these enzymes are linked to specific cellular functions and how they might be regulated. Here, we provide an indepth overview of polyphosphatase enzymes in budding yeast, which has served as a workhorse for polyP research, and in mammalian cells where the enzymes that make and degrade polyP have remained elusive. We identify critical open questions in both systems and propose strategies to guide future work.