Catalytic core of a membrane-associated eukaryotic polyphosphate polymerase

A systematic study of regulating inorganic polyphosphates production in Saccharomyces cerevisiae

Inorganic polyphosphate (polyP), a linear polymer of orthophosphate residues, plays critical roles in diverse biological processes spanning blood coagulation, immunomodulation, and post-translational protein modifications in eukaryotes. Notably, long-chain polyP (>100 phosphate units) exhibits distinct biological functionalities compared to shorter-chain counterparts. While Saccharomyces cerevisiae serves as a promising microbial platform for polyP biosynthesis, the genetic regulatory mechanisms underlying polyP metabolism remain poorly elucidated. Here, we systematically investigated the genetic determinants governing intracellular polyP levels and chain length dynamics in yeast. Through screening a library of 55 single-gene knockout strains, we identified six mutants (Δddp1, Δvip1, Δppn1, Δppn2, Δecm33, and Δccr4) exhibiting elevated polyP accumulation, whereas deletions of vtc1, kcs1, vma22, vma5, pho85, vtc4, vma2, vma3, ecm14, and vph2 resulted in near-complete polyP depletion. Subsequent combinatorial deletions in the Δppn1 background revealed that the Δppn1Δvip1 double mutant achieved synergistic enhancement in both polyP concentration (53.01 mg-P/g-DCW) and chain length, attributable to increased ATP availability and reduced polyphosphatase activity. Leveraging CRISPR/Cas9-mediated overexpression in Δppn1Δvip1, we engineered strain PP2 (vtc4 overexpression), which demonstrated a 2-fold increase in polyP yield (62.6 mg-P/g-DCW) relative to wild-type BY4741, with predominant synthesis of long-chain species. Mechanistically, qRT-PCR analysis confirmed that PP2 exhibited 46-fold up-regulation of vtc4 coupled with down-regulation of polyphosphatases encoding genes, ppn2, ddp1, and ppx1. This study performed a systematic study of regulating inorganic polyphosphates production in yeast and provides a synthetic biology strategy to engineer high-yield polyP-producing strains, advancing both fundamental understanding and biotechnological applications.

Transcriptomic response of marine dinoflagellate Prorocentrum cordatum to phosphorus deficiency

Phosphorus is crucial for marine phytoplankton viability as a key biogenic element. Under phosphorus deficiency, dinoflagellates exhibit changes in their feeding regime, alterations in transporters functioning, a reduction in cell proliferation rate and, in some cases, a transition to sexual reproduction. In this study, we performed RNA-sequencing analysis to assess the transcriptomic response of the dinoflagellate Prorocentrum cordatum to phosphorus deficiency in the cultivation medium. The aim of this work was to elucidate shifts in P. cordatum life cycle under these conditions focusing on the increase in the percentage of cells with a relative nuclear DNA content of 2C and the appearance of 4C cells, which may indicate a transition to the sexual process. We identified 196 differentially expressed genes - 169 up-regulated and 27 down-regulated-in cells grown for 14 days under phosphorus-depleted conditions. Analysis revealed up-regulation of pathways for phosphate uptake and assimilation, along with activation of RNA, protein, and lipid metabolic processes. Additionally, mechanisms regulating the cell cycle and inducing meiotic division were triggered. We identified up-regulated genes encoding proteins involved in meiotic recombination, including those promoting crossover. These findings indicate that phosphorus limitation can induce shift to sexual phase in P. cordatum life cycle.

Cost-effective urine recycling enabled by a synthetic osteoyeast platform for production of hydroxyapatite

Recycling human urine offers a sustainable solution to environmental challenges posed by conventional wastewater treatment. While it is possible to recover nutrients like nitrogen and phosphorus from urine, the low economic value of these products limits large-scale adoption. Here, we show that engineered yeast can convert urine into hydroxyapatite (HAp), a high-value biomaterial widely used in bone and dental applications. Inspired by the biological mechanisms of bone-forming cells, we develop a synthetic yeast platform osteoyeast, which uses enzymes to break down urea and increase the pH of the surrounding environment. This triggers the yeast vacuoles to accumulate calcium and phosphate as amorphous calcium phosphate, which is then secreted in vesicles and crystallized into HAp. We achieve HAp production at titers exceeding 1 g/L directly from urine. Techno-economic analysis demonstrates that this process offers clear economic and environmental advantages, making it a compelling strategy for high-value resource recovery from human waste.

The HOPS and vCLAMP protein Vam6 connects polyphosphate with mitochondrial function and oxidative stress resistance in Cryptococcus neoformans

Cryptococcus neoformans is considered one of the most dangerous fungal threats to human health, and the World Health Organization recently ranked it in the critical priority group for perceived public health importance. Proliferation of C. neoformans within mammalian hosts is supported by its ability to overcome nutritional limitations and endure stress conditions induced by the host immune response. Previously, we reported that the Vam6/Vps39/TRAP1-domain protein Vam6 was crucial for vacuolar morphology, iron acquisition, and virulence. However, the molecular mechanisms underlying the pleiotropic phenotypes resulting from loss of Vam6 remain poorly understood. In this study, we determined that Vam6 has roles in the HOPS complex for endomembrane trafficking to the vacuole and in the vCLAMP membrane contact site between the vacuole and mitochondria. Importantly, both of these roles regulate polyphosphate (polyP) metabolism, as demonstrated by a defect in trafficking of the VTC complex subunit Vtc2 for polyphosphate synthesis and by an influence on mitochondrial functions. In the latter case, Vam6 was required for polyP accumulation in response to electron transport chain inhibition and for overcoming oxidative stress. Overall, this work establishes connections between endomembrane trafficking, mitochondrial functions, and polyP homeostasis in C. neoformans.IMPORTANCEA detailed understanding of stress resistance by fungal pathogens of humans may provide new opportunities to improve antifungal therapy and combat life-threatening diseases. Here, we used a vam6 deletion mutant to investigate the role of the homotypic fusion and vacuole protein sorting (HOPS) complex in mitochondrial functions and polyphosphate homeostasis in Cryptococcus neoformans, an important fungal pathogen of immunocompromised people including those suffering from HIV/AIDS. Specifically, we made use of mutants defective in late endocytic trafficking steps to establish connections to oxidative stress and membrane trafficking with mitochondria. In particular, we found that mutants lacking the Vam6 protein had altered mitochondrial function, and that the mutants were perturbed for additional mitochondria and vacuole-related phenotypes (e.g., membrane composition, polyphosphate accumulation, and drug sensitivity). Overall, our study establishes connections between endomembrane trafficking components, mitochondrial functions, and polyphosphate homeostasis in an important fungal pathogen of humans.

Polyphosphatases have a polyphosphate-independent influence on the virulence of Cryptococcus neoformans

Cryptococcus neoformans, an invasive basidiomycete fungal pathogen, causes one of the most prevalent, life-threatening diseases in immunocompromised individuals and accounts for ~19% of AIDS-associated deaths. Therefore, understanding the pathogenesis of C. neoformans and its interactions with the host immune system is critical for developing therapeutics against cryptococcosis. Previous studies demonstrated that C. neoformans cells lacking polyphosphate (polyP), an immunomodulatory polyanionic storage molecule, display altered cell surface architecture but unimpaired virulence in a murine model of cryptococcosis. However, the relevance of cell surface changes and the role of hyperaccumulation of polyP in the virulence of C. neoformans remain unclear. Here we show that mutants with abundant polyP due to loss of the polyphosphatases Xpp1 and Epp1 are attenuated for virulence. The double mutant differed from the wild type during disease by demonstrating a higher fungal burden in disseminated organs at the experimental endpoint and by provoking an altered immune response. An analysis of triple mutants lacking the polyphosphatases and the Vtc4 protein for polyP synthesis also caused attenuated virulence in mice, thus suggesting an influence of Xpp1 and/or Epp1 independent of polyP levels. A more detailed characterization revealed that Xpp1 and Epp1 play multiple roles by contributing to the organization of the cell surface, virulence factor production, the response to stress, and mitochondrial function. Overall, we conclude that polyphosphatases have additional functions in the pathobiology of C. neoformans beyond an influence on polyP levels.IMPORTANCECryptococcus neoformans causes one of the most prevalent fungal diseases in people with compromised immune systems and accounts for ~19% of AIDS-associated deaths worldwide. The continual increase in the incidence of fungal infections and limited treatment options necessitate the development of new antifungal drugs and improved diagnostics. Polyphosphate (polyP), an under-explored biopolymer, functions as a storage molecule, modulates the host immune response, and contributes to the ability of some fungal and bacterial pathogens to cause disease. However, the role of polyP in cryptococcal disease remains unclear. In this study, we report that the polyphosphatase enzymes that regulate polyP synthesis and turnover contribute to the virulence of C. neoformans in a mouse model of cryptococcosis. The polyphosphatases influenced the survival of C. neoformans in macrophages and altered the host immune response. In addition, the mutants lacking the enzymes have changes in cell surface architecture and size, as well as defects in both mitochondrial function and the stress response. By using mutants defective in the polyphosphatases and polyP synthesis, we demonstrate that many of the phenotypic contributions of the polyphosphatases are independent of polyP.

The combination of ultraviolet mutagenesis and PPX1 overexpression synergistically enhanced S-adenosyl-L-methionine synthesis in industrial Saccharomyces cerevisiae

S-adenosyl-L-methionine (SAM) is the only injectable drug among the hepatoprotective and choleretic drugs, which has remarkable efficacy and is favored by hepatopaths. The demand for SAM is constantly increasing in clinical settings. Therefore, many efforts have been made to increase SAM biosynthesis from L-methionine and ATP in Saccharomyces cerevisiae. This study aimed to construct a stable and high-accumulating SAM industrial strain through successive ultraviolet irradiation (UV) mutations coupled with three resistant (ethionine, nystatin, and cordycepin, respectively) screening procedures and metabolic engineering strategies. Following multiple UV mutagenesis, a higher production mutant strain ZJT15-33 was successfully obtained. In addition, the recombinant strain spe2△-PPX1 was derived from ZJT15-33 by deleting the SPE2 and overexpressing the PPX1, resulting in a 2.5-fold enhanced ATP accumulation, which promoted the synthesis of 2.41 g/L SAM in the shake-flask, representing an 11.4-fold enhancement over the original strain (0.21 g/L). Furthermore, 11.65 g/L SAM was accumulated with 113 mg/g DCW SAM content in a 5-L fermenter at 96 h, marking a 36.57 % increase compared to strain ZJT15-33 (8.53 g/L). These results indicated that UV mutagenesis combined with PPX1 overexpression could effectively improve SAM synthesis in S. cerevisiae, providing a feasible approach for developing highly SAM industrial production.

Bacterial Hachiman complex executes DNA cleavage for antiphage defense

Bacteria have developed a variety of immune systems to combat phage infections. The Hachiman system is a novel prokaryotic antiphage defense system comprising HamA and HamB proteins, which contains the DUF1837 and helicase domains, respectively. However, the defense mechanism remains only partially understood. Here, we present the cryo-electron microscopy (cryo-EM) structure of the Hachiman defense system featuring a fusion of Cap4 nuclease domain within HamA. Further structure analysis indicates that the DUF1837 domain on HamA resembles the PD-(D/E)XK nuclease but lacks active sites. Bioinformatics analysis reveals that catalytically inactive DUF1837 domains often recruit other functional domains to fulfill anti-phage defense. HamA interacts with HamB to form a heterodimer HamAB to mediate ATP hydrolysis and execute DNA cleavage, thus implementing antiphage defense. Our findings elucidate the structural basis of the Hachiman defense complex, highlighting the critical roles of the helicase and nuclease in prokaryotic immunity.

A fusion protein of polyphosphate kinase 1 (PPK1) and a Nudix hydrolase is involved in inorganic polyphosphate accumulation in the unicellular red alga Cyanidioschyzon merolae

Inorganic polyphosphate (polyP) is a linear polymer of phosphate that plays various roles in cells, including in phosphate and metal homeostasis. Homologs of the vacuolar transporter chaperone 4 (VTC4), catalyzing polyP synthesis in many eukaryotes, are absent in red algae, which are among the earliest divergent plant lineages. We identified homologs of polyphosphate kinase 1 (PPK1), a conserved polyP synthase in bacteria, in 42 eukaryotic genomes, including 31 species detected in this study and 12 species of red algae. Phylogenetic analysis suggested that most eukaryotic PPK1 homologs originated from horizontal gene transfer from a prokaryote to a plant before the divergence of red algae and Viridiplantae. In red algae, the homologs were fused to a nucleoside diphosphate-linked moiety X (Nudix) hydrolase of the diphosphoinositol polyphosphate phosphohydrolase (DIPP) family. We characterized the fusion protein CmPPK1 in the unicellular red alga Cyanidioschyzon merolae, which has been used in studies on basic features of eukaryotes. In the knockout strain ∆CmPPK1, polyP was undetectable, suggesting a primary role for CmPPK1 in polyP synthesis. In addition, ∆CmPPK1 showed altered metal balance. Mutations in the catalytically important residues of the Nudix hydrolase domain (NHD) either increased or decreased polyP contents. Both high and low polyP NHD mutants were susceptible to phosphate deprivation, indicating that adequate NHD function is necessary for normal phosphate starvation responses. The results reveal the unique features of PPK1 in red algae and promote further investigation of polyP metabolism and functions in red algae and eukaryotic evolution.

Analysis of polyphosphate in mammalian cells and tissues: methods, functions and challenges

Polyphosphates play a crucial role in various biological processes, such as blood coagulation, energy homeostasis, and cellular stress response. However, their isolation, detection, and quantification present significant challenges. These difficulties arise primarily from their solubility, low concentration in mammals, and structural similarity to other ubiquitous biopolymers. This review provides an overview of the current understanding of polyphosphates in mammals, including their proposed functions and tissue distribution. It also examines key isolation techniques, such as chromatography and precipitation, alongside detection methods, such as colorimetric assays and enzymatic digestion. The strengths and limitations of these methods are discussed, as well as the challenges in preserving polyphosphate integrity. Recent advancements in isolation and detection are also highlighted, offering a comprehensive perspective essential for advancing polyphosphate research.

Ppn2 Polyphosphatase Improves the Ability of S. cerevisiae to Grow in Mild Alkaline Medium

Inorganic polyphosphates and respective metabolic pathways and enzymes are important factors for yeast active growth in unfavorable conditions. However, particular proteins of polyphosphate metabolism remain poorly explored in this context. Here we report biochemical and transcriptomic characterization of the CRN/PPN2 yeast strain (derived from Ppn1-lacking CRN strain) overexpressing poorly studied Ppn2 polyphosphatase. We showed that Ppn2 overexpression significantly reduced lag phase in the alkaline medium presumably due to the ability of Ppn2 to efficiently hydrolyze inorganic polyphosphates and thus neutralize hydroxide ions in the cell. With RNA-Seq, we compared the molecular phenotypes of CRN/PPN2 and its parent CRN strain grown in YPD or alkaline medium and detected transcriptomic changes induced by Ppn2 overexpression and reflecting the adaptation to alkaline conditions. The core set of upregulated genes included several genes with a previously unknown function. Respective knockout strains (∆ecm8, ∆yol160w, ∆cpp3, ∆ycr099c) exhibited defects of growth or cell morphology in the alkaline medium, proving the functional involvement of the respective proteins in sustaining growth in alkaline conditions.

Prospects of phosphate solubilizing microorganisms in sustainable agriculture

Phosphorus (P), an essential macronutrient for various plant processes, is generally a limiting soil component for crop growth and yields. Organic and inorganic types of P are copious in soils, but their phyto-availability is limited as it is present largely in insoluble forms. Although phosphate fertilizers are applied in P-deficit soils, their undue use negatively impacts soil quality and the environment. Moreover, many P fertilizers are lost because of adsorption and fixation mechanisms, further reducing fertilizer efficiencies. The application of phosphate-solubilizing microorganisms (PSMs) is an environmentally friendly, low-budget, and biologically efficient method for sustainable agriculture without causing environmental hazards. These beneficial microorganisms are widely distributed in the rhizosphere and can hydrolyze inorganic and organic insoluble P substances to soluble P forms which are directly assimilated by plants. The present review summarizes and discusses our existing understanding related to various forms and sources of P in soils, the importance and P utilization by plants and microbes,, the diversification of PSMs along with mixed consortia of diverse PSMs including endophytic PSMs, the mechanism of P solubilization, and lastly constraints being faced in terms of production and adoption of PSMs on large scale have also been discussed.

An Update on Polyphosphate In Vivo Activities

Polyphosphate (polyP) is an evolutionary ancient inorganic molecule widespread in biology, exerting a broad range of biological activities. The intracellular polymer serves as an energy storage pool and phosphate/calcium ion reservoir with implications for basal cellular functions. Metabolisms of the polymer are well understood in procaryotes and unicellular eukaryotic cells. However, functions, regulation, and association with disease states of the polymer in higher eukaryotic species such as mammalians are just beginning to emerge. The review summarises our current understanding of polyP metabolism, the polymer's functions, and methods for polyP analysis. In-depth knowledge of the pathways that control polyP turnover will open future perspectives for selective targeting of the polymer.

Polyphosphate Nanoparticles: Balancing Energy Requirements in Tissue Regeneration Processes

Nanoparticles of a particular, evolutionarily old inorganic polymer found across the biological kingdoms have attracted increasing interest in recent years not only because of their crucial role in metabolism but also their potential medical applicability: it is inorganic polyphosphate (polyP). This ubiquitous linear polymer is composed of 10-1000 phosphate residues linked by high-energy anhydride bonds. PolyP causes induction of gene activity, provides phosphate for bone mineralization, and serves as an energy supplier through enzymatic cleavage of its acid anhydride bonds and subsequent ATP formation. The biomedical breakthrough of polyP came with the development of a successful fabrication process, in depot form, as Ca- or Mg-polyP nanoparticles, or as the directly effective polymer, as soluble Na-polyP, for regenerative repair and healing processes, especially in tissue areas with insufficient blood supply. Physiologically, the platelets are the main vehicles for polyP nanoparticles in the circulating blood. To be biomedically active, these particles undergo coacervation. This review provides an overview of the properties of polyP and polyP nanoparticles for applications in the regeneration and repair of bone, cartilage, and skin. In addition to studies on animal models, the first successful proof-of-concept studies on humans for the healing of chronic wounds are outlined.

The Protein Scaffolding Functions of Polyphosphate

Inorganic polyphosphate (polyP), one of the first high-energy compound on earth, defies its extreme compositional and structural simplicity with an astoundingly wide array of biological activities across all domains of life. However, the underlying mechanism of such functional pleiotropy remains largely elusive. In this review, we will summarize recent studies demonstrating that this simple polyanion stabilizes protein folding intermediates and scaffolds select native proteins. These functions allow polyP to act as molecular chaperone that protects cells against protein aggregation, as pro-amyloidogenic factor that accelerates both physiological and disease-associated amyloid formation, and as a modulator of liquid-liquid phase separation processes. These activities help to explain polyP's known roles in bacterial stress responses and pathogenicity, provide the mechanistic foundation for its potential role in human neurodegenerative diseases, and open a new direction regarding its influence on gene expression through condensate formation. We will highlight critical unanswered questions and point out potential directions that will help to further understand the pleiotropic functions of this ancient and ubiquitous biopolymer.

A mammalian model reveals inorganic polyphosphate channeling into the nucleolus and induction of a hyper-condensate state

Inorganic polyphosphate (polyP) is a ubiquitous polymer that controls fundamental processes. To overcome the absence of a genetically tractable mammalian model, we developed an inducible mammalian cell line expressing Escherichia coli polyphosphate kinase 1 (EcPPK1). Inducing EcPPK1 expression prompted polyP synthesis, enabling validation of polyP analytical methods. Virtually all newly synthesized polyP accumulates within the nucleus, mainly in the nucleolus. The channeled polyP within the nucleolus results in the redistribution of its markers, leading to altered rRNA processing. Ultrastructural analysis reveals electron-dense polyP structures associated with a hyper-condensed nucleolus resulting from an exacerbation of the liquid-liquid phase separation (LLPS) phenomena controlling this membraneless organelle. The selective accumulation of polyP in the nucleoli could be interpreted as an amplification of polyP channeling to where its physiological function takes place. Indeed, quantitative analysis of several mammalian cell lines confirms that endogenous polyP accumulates within the nucleolus.

Characterization of polyphosphate dynamics in the widespread freshwater diatom Achnanthidium minutissimum under varying phosphorus supplies

Polyphosphates (polyP) are ubiquitous biomolecules that play a multitude of physiological roles in many cells. We have studied the presence and role of polyP in a unicellular alga, the freshwater diatom Achnanthidium minutissimum. This diatom stores up to 2.0 pg·cell-1 of polyP, with chain lengths ranging from 130 to 500 inorganic phosphate units (Pi). We applied energy dispersive X-ray spectroscopy, Raman/fluorescence microscopy, and biochemical assays to localize and characterize the intracellular polyP granules that were present in large apical vacuoles. We investigated the fate of polyP in axenic A. minutissimum cells grown under phosphorus (P), replete (P(+)), or P deplete (P(-)) cultivation conditions and observed that in the absence of exogenous P, A. minutissimum rapidly utilizes their internal polyP reserves, maintaining their intrinsic growth rates for up to 8 days. PolyP-depleted A. minutissimum cells rapidly took up exogenous P a few hours after Pi resupply and generated polyP three times faster than cells that were not initially subjected to P limitation. Accordingly, we propose that A. minutissimum deploys a succession of acclimation strategies regarding polyP dynamics where the production or consumption of polyP plays a central role in the homeostasis of the diatom.

The ring rules the chain - inositol pyrophosphates and the regulation of inorganic polyphosphate

The maintenance of phosphate homeostasis serves as a foundation for energy metabolism and signal transduction processes in all living organisms. Inositol pyrophosphates (PP-InsPs), composed of an inositol ring decorated with monophosphate and diphosphate moieties, and inorganic polyphosphate (polyP), chains of orthophosphate residues linked by phosphoanhydride bonds, are energy-rich biomolecules that play critical roles in phosphate homeostasis. There is a complex interplay between these two phosphate-rich molecules, and they share an interdependent relationship with cellular adenosine triphosphate (ATP) and inorganic phosphate (Pi). In eukaryotes, the enzymes involved in PP-InsP synthesis show some degree of conservation across species, whereas distinct enzymology exists for polyP synthesis among different organisms. In fact, the mechanism of polyP synthesis in metazoans, including mammals, is still unclear. Early studies on PP-InsP and polyP synthesis were conducted in the slime mould Dictyostelium discoideum, but it is in the budding yeast Saccharomyces cerevisiae that a clear understanding of the interplay between polyP, PP-InsPs, and Pi homeostasis has now been established. Recent research has shed more light on the influence of PP-InsPs on polyP in mammals, and the regulation of both these molecules by cellular ATP and Pi levels. In this review we will discuss the cross-talk between PP-InsPs, polyP, ATP, and Pi in the context of budding yeast, slime mould, and mammals. We will also highlight the similarities and differences in the relationship between these phosphate-rich biomolecules among this group of organisms.

Key Proteomics Tools for Fundamental and Applied Microalgal Research

Microscopic, photosynthetic prokaryotes and eukaryotes, collectively referred to as microalgae, are widely studied to improve our understanding of key metabolic pathways (e.g., photosynthesis) and for the development of biotechnological applications. Omics technologies, which are now common tools in biological research, have been shown to be critical in microalgal research. In the past decade, significant technological advancements have allowed omics technologies to become more affordable and efficient, with huge datasets being generated. In particular, where studies focused on a single or few proteins decades ago, it is now possible to study the whole proteome of a microalgae. The development of mass spectrometry-based methods has provided this leap forward with the high-throughput identification and quantification of proteins. This review specifically provides an overview of the use of proteomics in fundamental (e.g., photosynthesis) and applied (e.g., lipid production for biofuel) microalgal research, and presents future research directions in this field.

Advances in the cellular biology, biochemistry, and molecular biology of acidocalcisomes

SUMMARYAcidocalcisomes are organelles conserved during evolution and closely related to the so-called volutin granules of bacteria and archaea, to the acidocalcisome-like vacuoles of yeasts, and to the lysosome-related organelles of animal species. All these organelles have in common their acidity and high content of polyphosphate and calcium. They are characterized by a variety of functions from storage of phosphorus and calcium to roles in Ca2+ signaling, osmoregulation, blood coagulation, and inflammation. They interact with other organelles through membrane contact sites or by fusion, and have several enzymes, pumps, transporters, and channels.

The Physiological Inorganic Polymers Biosilica and Polyphosphate as Key Drivers for Biomedical Materials in Regenerative Nanomedicine

There is a need for novel nanomaterials with properties not yet exploited in regenerative nanomedicine. Based on lessons learned from the oldest metazoan phylum, sponges, it has been recognized that two previously ignored or insufficiently recognized principles play an essential role in tissue regeneration, including biomineral formation/repair and wound healing. Firstly, the dependence on enzymes as a driving force and secondly, the availability of metabolic energy. The discovery of enzymatic synthesis and regenerative activity of amorphous biosilica that builds the mineral skeleton of siliceous sponges formed the basis for the development of successful strategies for the treatment of osteochondral impairments in humans. In addition, the elucidation of the functional significance of a second regeneratively active inorganic material, namely inorganic polyphosphate (polyP) and its amorphous nanoparticles, present from sponges to humans, has pushed forward the development of innovative materials for both soft (skin, cartilage) and hard tissue (bone) repair. This energy-rich molecule exhibits a property not shown by any other biopolymer: the delivery of metabolic energy, even extracellularly, necessary for the ATP-dependent tissue regeneration. This review summarizes the latest developments in nanobiomaterials based on these two evolutionarily old, regeneratively active materials, amorphous silica and amorphous polyP, highlighting their specific, partly unique properties and mode of action, and discussing their possible applications in human therapy. The results of initial proof-of-concept studies on patients demonstrating complete healing of chronic wounds are outlined.

IP8: A quantitatively minor inositol pyrophosphate signaling molecule that punches above its weight

The inositol pyrophosphates (PP-IPs) are specialized members of the wider inositol phosphate signaling family that possess functionally significant diphosphate groups. The PP-IPs exhibit remarkable functionally versatility throughout the eukaryotic kingdoms. However, a quantitatively minor PP-IP - 1,5 bisdiphosphoinositol tetrakisphosphate (1,5-IP8) - has received considerably less attention from the cell signalling community. The main purpose of this review is to summarize recently-published data which have now brought 1,5-IP8 into the spotlight, by expanding insight into the molecular mechanisms by which this polyphosphate regulates many fundamental biological processes.

Phosphate uptake restriction, phosphate export, and polyphosphate synthesis contribute synergistically to cellular proliferation and survival

Phosphate (Pi) is a macronutrient, and Pi homeostasis is essential for life. Pi homeostasis has been intensively studied; however, many questions remain, even at the cellular level. Using Schizosaccharomyces pombe, we sought to better understand cellular Pi homeostasis and showed that three Pi regulators with SPX domains, Xpr1/Spx2, Pqr1, and the VTC complex synergistically contribute to Pi homeostasis to support cell proliferation and survival. SPX domains bind to inositol pyrophosphate and modulate activities of Pi-related proteins. Xpr1 is a plasma membrane protein and its Pi-exporting activity has been demonstrated in metazoan orthologs, but not in fungi. We first found that S. pombe Xpr1 is a Pi exporter, activity of which is regulated and accelerated in the mutants of Pqr1 and the VTC complex. Pqr1 is the ubiquitin ligase downregulating the Pi importers, Pho84 and Pho842. The VTC complex synthesizes polyphosphate in vacuoles. Triple deletion of Xpr1, Pqr1, and Vtc4, the catalytic core of the VTC complex, was nearly lethal in normal medium but survivable at lower [Pi]. All double-deletion mutants of the three genes were viable at normal Pi, but Δpqr1Δxpr1 showed severe viability loss at high [Pi], accompanied by hyper-elevation of cellular total Pi and free Pi. This study suggests that the three cellular processes, restriction of Pi uptake, Pi export, and polyP synthesis, contribute synergistically to cell proliferation through maintenance of Pi homeostasis, leading to the hypothesis that cooperation between Pqr1, Xpr1, and the VTC complex protects the cytoplasm and/or the nucleus from lethal elevation of free Pi.

Non-Hydrolysable Analogues of Cyclic and Branched Condensed Phosphates: Chemistry and Chemical Proteomics

Studies into the biology of condensed phosphates almost exclusively cover linear polyphosphates. However, there is evidence for the presence of cyclic polyphosphates (metaphosphates) in organisms and for enzymatic digestion of branched phosphates (ultraphosphates) with alkaline phosphatase. Further research of non-linear condensed phosphates in biology would profit from interactome data of such molecules, however, their stability in biological media is limited. Here we present syntheses of modified, non-hydrolysable analogues of cyclic and branched condensed phosphates, called meta- and ultraphosphonates, and their application in a chemical proteomics approach using yeast cell extracts. We identify putative interactors with overlapping hits for structurally related capture compounds underlining the quality of our results. The datasets serve as starting point to study the biological relevance and functions of meta- and ultraphosphates. In addition, we examine the reactivity of meta- and ultraphosphonates with implications for their "hydrolysable" analogues: Efforts to increase the ring-sizes of meta- or cyclic ultraphosphonates revealed a strong preference to form trimetaphosphate-analogue structures by cyclization and/or ring-contraction. Using carbodiimides for condensation, the so far inaccessible dianhydro product of ultraphosphonate, corresponding to P4 O11 2- , was selectively obtained and then ring-opened by different nucleophiles yielding modified cyclic ultraphosphonates.

Variation in intracellular polyphosphate and associated gene expression in response to different phosphorus conditions in the dinoflagellate Karenia mikimotoi

Polyphosphate (polyP) has long been recognized as a crucial intracellular reservoir for phosphorus in microorganisms. However, the dynamics of polyP and its regulatory mechanism in eukaryotic phytoplankton in response to variations in external phosphorus conditions remain poorly understood. A comprehensive investigation was conducted to examine the intracellular polyP-associated metabolic response of the dinoflagellate Karenia mikimotoi, a harmful algal bloom species, through integrated physiological, biochemical, and transcriptional analyses under varying external phosphorus conditions. Comparable growth curves and Fv/Fm between phosphorus-replete conditions and phosphorus-depleted conditions suggested that K. mikimotoi has a strong capability to mobilize the intracellular phosphorus pool for growth under phosphorus deficiency. Intracellular phosphate (IPi) and polyP contributed approximately 6-23 % and 1-3 %, respectively, to the overall particulate phosphorus (PP) content under different phosphorus conditions. The significant decrease in PP and increase in polyP:PP suggested that cellular phosphorus components other than polyP are preferred for utilization under phosphorus deficiency. Genes involved in polyP synthesis and hydrolysis were upregulated to maintain phosphorus homeostasis in K. mikimotoi. These findings provide novel insights into the specific cellular strategies for phosphorus storage and the transcriptional response in intracellular polyP metabolism in K. mikimotoi. Additionally, these results also indicate that polyP may not play a crucial role in cellular phosphorus storage in phytoplankton, at least in dinoflagellates.

Vtc4 Promotes the Entry of Phagophores into Vacuoles in the Saccharomyces cerevisiae Snf7 Mutant Cell

Endocytosis and autophagy are the main pathways to deliver cargoes in vesicles and autophagosomes, respectively, to vacuoles/lysosomes in eukaryotes. Multiple positive regulators but few negative ones are reported to regulate the entry of vesicles and autophagosomes into vacuoles/lysosomes. In yeast, the Rab5 GTPase Vps21 and the ESCRT (endosomal sorting complex required for transport) are positive regulators in endocytosis and autophagy. During autophagy, Vps21 regulates the ESCRT to phagophores (unclosed autophagosomes) to close them. Phagophores accumulate on vacuolar membranes in both vps21∆ and ESCRT mutant cells under a short duration of nitrogen starvation. The vacuolar transport chaperon (VTC) complex proteins are recently found to be negative regulators in endocytosis and autophagy. Phagophores in vps21∆ cells are promoted to enter vacuoles when the VTC complex proteins are absent. Phagophores are easily observed inside vacuoles when any of these VTC complex proteins (Vtc1, 2, 4, 5) are removed. However, it is unknown whether the removal of VTC complex proteins will also promote the entry of phagophores into vacuoles in ESCRT mutant cells under the same conditions. Snf7 is a core subunit of ESCRT subcomplex III (ESCRT-III), and phagophores accumulate in snf7∆ cells under a short duration of nitrogen starvation. We used green fluorescence protein (GFP) labeled Atg8 to display phagophores and FM4-64-stained or Vph1-GFP-labeled membrane structures to show vacuoles, then examined fluorescence localization and GFP-Atg8 degradation in snf7∆ and snf7∆vtc4∆ cells. Results showed that Vtc4 depletion promoted the entry of phagophores in snf7∆ cells into vacuoles as it did for vps21∆ cells, although the promotion level was more obvious in vps21∆ cells. This observation indicates that the VTC complex proteins may have a widespread role in negatively regulating cargos to enter vacuoles in yeast.

Modification of histidine repeat proteins by inorganic polyphosphate

Inorganic polyphosphate (polyP) is a linear polymer of orthophosphate that is present in nearly all organisms studied to date. A remarkable function of polyP involves its attachment to lysine residues via non-enzymatic post-translational modification (PTM), which is presumed to be covalent. Here, we show that proteins containing tracts of consecutive histidine residues exhibit a similar modification by polyP, which confers an electrophoretic mobility shift on NuPAGE gels. Our screen uncovers 30 human and yeast histidine repeat proteins that undergo histidine polyphosphate modification (HPM). This polyP modification is histidine dependent and non-covalent in nature, although remarkably it withstands harsh denaturing conditions-a hallmark of covalent PTMs. Importantly, we show that HPM disrupts phase separation and the phosphorylation activity of the human protein kinase DYRK1A, and inhibits the activity of the transcription factor MafB, highlighting HPM as a potential protein regulatory mechanism.

The Extracellular Vesicles Containing Inorganic Polyphosphate of Candida Yeast upon Growth on Hexadecane

The cell wall of Candida yeast grown on presence of hexadecane as a sole carbon source undergoes structural and functional changes including the formation of specific supramolecular complexes-canals. The canals contain specific polysaccharides and enzymes that provide primary oxidization of alkanes. In addition, inorganic polyphosphate (polyP) was identified in Candida maltosa canals. The aim of the work was a comparative study of the features of cell walls and extracellular structures in yeast C. maltosa, C. albicans and C. tropicalis with special attention to inorganic polyphosphates as possible part of these structures when grown on the widely used xenobiotic hexadecane (diesel fuel). Fluorescence microscopy with DAPI has shown an unusual localization of polyP on the cell surface and in the exovesicles in the three yeast species, when growing on hexadecane. Electron-scanning microscopy showed that the exovesicles were associated with the cell wall and also presented in the external environment probably as biofilm components. Treatment of hexadecane-grown cells with purified Ppx1 polyphosphatase led to the release of phosphate into the incubation medium and the disappearance of polyP in vesicles and cell wall observed using microscopic methods. The results indicate the important role of polyP in the formation of extracellular structures in the Candida yeast when consuming hexadecane and are important for the design of xenobiotic destructors based on yeast or mixed cultures.

Inositol pyrophosphate dynamics reveals control of the yeast phosphate starvation program through 1,5-IP8 and the SPX domain of Pho81

Eukaryotic cells control inorganic phosphate to balance its role as essential macronutrient with its negative bioenergetic impact on reactions liberating phosphate. Phosphate homeostasis depends on the conserved INPHORS signaling pathway that utilizes inositol pyrophosphates and SPX receptor domains. Since cells synthesize various inositol pyrophosphates and SPX domains bind them promiscuously, it is unclear whether a specific inositol pyrophosphate regulates SPX domains in vivo, or whether multiple inositol pyrophosphates act as a pool. In contrast to previous models, which postulated that phosphate starvation is signaled by increased production of the inositol pyrophosphate 1-IP7, we now show that the levels of all detectable inositol pyrophosphates of yeast, 1-IP7, 5-IP7, and 1,5-IP8, strongly decline upon phosphate starvation. Among these, specifically the decline of 1,5-IP8 triggers the transcriptional phosphate starvation response, the PHO pathway. 1,5-IP8 inactivates the cyclin-dependent kinase inhibitor Pho81 through its SPX domain. This stimulates the cyclin-dependent kinase Pho85-Pho80 to phosphorylate the transcription factor Pho4 and repress the PHO pathway. Combining our results with observations from other systems, we propose a unified model where 1,5-IP8 signals cytosolic phosphate abundance to SPX proteins in fungi, plants, and mammals. Its absence triggers starvation responses.

Overexpression of polyphosphate polymerases and deletion of polyphosphate phosphatases shorten the replicative lifespan in yeast

We previously found that overexpression of phosphate starvation-responsive genes by disrupting PHO80 led to a shortened replicative lifespan in yeast. To identify lifespan-related genes, we screened upregulated genes in the pho80Δ mutant and focused on the VTC genes, which encode the vacuolar polyphosphate (polyP) polymerase complex. VTC1/VTC2/VTC4 deletion restored the lifespan and intracellular polyP levels in pho80Δ. In the wild type, overexpression of VTC5 or a combination of the other VTCs caused high polyP accumulation and shortened lifespan. Similar phenotypes were caused by the deletion of polyP phosphatase genes-vacuolar PPN1 and cytosolic PPX1. The polyP-accumulating strains exhibited stress sensitivities. Thus, we demonstrated that polyP metabolic enzymes participate in replicative lifespan, and extreme polyP accumulation shortens the lifespan.

Interaction of calcium responsive proteins and transcriptional factors with the PHO regulon in yeasts and fungi

Phosphate and calcium ions are nutrients that play key roles in growth, differentiation and the production of bioactive secondary metabolites in filamentous fungi. Phosphate concentration regulates the biosynthesis of hundreds of fungal metabolites. The central mechanisms of phosphate transport and regulation, mediated by the master Pho4 transcriptional factor are known, but many aspects of the control of gene expression need further research. High ATP concentration in the cells leads to inositol pyrophosphate molecules formation, such as IP3 and IP7, that act as phosphorylation status reporters. Calcium ions are intracellular messengers in eukaryotic organisms and calcium homeostasis follows elaborated patterns in response to different nutritional and environmental factors, including cross-talking with phosphate concentrations. A large part of the intracellular calcium is stored in vacuoles and other organelles forming complexes with polyphosphate. The free cytosolic calcium concentration is maintained by transport from the external medium or by release from the store organelles through calcium permeable transient receptor potential (TRP) ion channels. Calcium ions, particularly the free cytosolic calcium levels, control the biosynthesis of fungal metabolites by two mechanisms, 1) direct interaction of calcium-bound calmodulin with antibiotic synthesizing enzymes, and 2) by the calmodulin-calcineurin signaling cascade. Control of very different secondary metabolites, including pathogenicity determinants, are mediated by calcium through the Crz1 factor. Several interactions between calcium homeostasis and phosphate have been demonstrated in the last decade: 1) The inositol pyrophosphate IP3 triggers the release of calcium ions from internal stores into the cytosol, 2) Expression of the high affinity phosphate transporter Pho89, a Na+/phosphate symporter, is controlled by Crz1. Also, mutants defective in the calcium permeable TRPCa7-like of Saccharomyces cerevisiae shown impaired expression of Pho89. This information suggests that CrzA and Pho89 play key roles in the interaction of phosphate and calcium regulatory pathways, 3) Finally, acidocalcisomes organelles have been found in mycorrhiza and in some melanin producing fungi that show similar characteristics as protozoa calcisomes. In these organelles there is a close interaction between orthophosphate, pyrophosphate and polyphosphate and calcium ions that are absorbed in the polyanionic polyphosphate matrix. These advances open new perspectives for the control of fungal metabolism.

Metabolic Consequences of Polyphosphate Synthesis and Imminent Phosphate Limitation

Cells stabilize intracellular inorganic phosphate (Pi) to compromise between large biosynthetic needs and detrimental bioenergetic effects of Pi. Pi homeostasis in eukaryotes uses Syg1/Pho81/Xpr1 (SPX) domains, which are receptors for inositol pyrophosphates. We explored how polymerization and storage of Pi in acidocalcisome-like vacuoles supports Saccharomyces cerevisiae metabolism and how these cells recognize Pi scarcity. Whereas Pi starvation affects numerous metabolic pathways, beginning Pi scarcity affects few metabolites. These include inositol pyrophosphates and ATP, a low-affinity substrate for inositol pyrophosphate-synthesizing kinases. Declining ATP and inositol pyrophosphates may thus be indicators of impending Pi limitation. Actual Pi starvation triggers accumulation of the purine synthesis intermediate 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), which activates Pi-dependent transcription factors. Cells lacking inorganic polyphosphate show Pi starvation features already under Pi-replete conditions, suggesting that vacuolar polyphosphate supplies Pi for metabolism even when Pi is abundant. However, polyphosphate deficiency also generates unique metabolic changes that are not observed in starving wild-type cells. Polyphosphate in acidocalcisome-like vacuoles may hence be more than a global phosphate reserve and channel Pi to preferred cellular processes. IMPORTANCE Cells must strike a delicate balance between the high demand of inorganic phosphate (Pi) for synthesizing nucleic acids and phospholipids and its detrimental bioenergetic effects by reducing the free energy of nucleotide hydrolysis. The latter may stall metabolism. Therefore, microorganisms manage the import and export of phosphate, its conversion into osmotically inactive inorganic polyphosphates, and their storage in dedicated organelles (acidocalcisomes). Here, we provide novel insights into metabolic changes that yeast cells may use to signal declining phosphate availability in the cytosol and differentiate it from actual phosphate starvation. We also analyze the role of acidocalcisome-like organelles in phosphate homeostasis. This study uncovers an unexpected role of the polyphosphate pool in these organelles under phosphate-rich conditions, indicating that its metabolic roles go beyond that of a phosphate reserve for surviving starvation.

Dimorphism of Candida tropicalis and its effect on nitrogen and phosphorus removal and sludge settleability

Candida tropicalis PNY, a novel dimorphic strain with the capacity of simultaneous carbon, nitrogen and phosphorus removal in anaerobic and aerobic conditions, was isolated from activated sludge. Dimorphism of C. tropicalis PNY had effect on removing nitrogen and phosphorous and slightly affected COD removal under aerobic condition. Sample with high hypha formation rate (40 ± 5%) had more removal efficiencies of NH₄⁺-N (50 mg/L) and PO₄^3--P (10 mg/L), which could achieve 82.19% and 97.53%, respectively. High hypha cells dosage exhibited good settleability and filamentous overgrowth was not observed. According to label-free quantitative proteomics assays. Up-regulated proteins involved in the mitogen-activated protein kinase (MAPK) pathway indicated the active growth and metabolism process of sample with high hypha formation rate (40 ± 5%). And proteins concerning about glutamate synthetase and SPX domain-contain protein explain for the nutrient removal mechanism including assimilation of ammonia and polyphosphates synthesis.

Cryo-EM structure of the polyphosphate polymerase VTC reveals coupling of polymer synthesis to membrane transit

The eukaryotic vacuolar transporter chaperone (VTC) complex acts as a polyphosphate (polyP) polymerase that synthesizes polyP from adenosine triphosphate (ATP) and translocates polyP across the vacuolar membrane to maintain an intracellular phosphate (Pi ) homeostasis. To discover how the VTC complex performs its function, we determined a cryo-electron microscopy structure of an endogenous VTC complex (Vtc4/Vtc3/Vtc1) purified from Saccharomyces cerevisiae at 3.1 Å resolution. The structure reveals a heteropentameric architecture of one Vtc4, one Vtc3, and three Vtc1 subunits. The transmembrane region forms a polyP-selective channel, likely adopting a resting state conformation, in which a latch-like, horizontal helix of Vtc4 limits the entrance. The catalytic Vtc4 central domain is located on top of the pseudo-symmetric polyP channel, creating a strongly electropositive pathway for nascent polyP that can couple synthesis to translocation. The SPX domain of the catalytic Vtc4 subunit positively regulates polyP synthesis by the VTC complex. The noncatalytic Vtc3 regulates VTC through a phosphorylatable loop. Our findings, along with the functional data, allow us to propose a mechanism of polyP channel gating and VTC complex activation.

Inositol pyrophosphates activate the vacuolar transport chaperone complex in yeast by disrupting a homotypic SPX domain interaction

Many proteins involved in eukaryotic phosphate homeostasis are regulated by SPX domains. In yeast, the vacuolar transporter chaperone (VTC) complex contains two such domains, but mechanistic details of its regulation are not well understood. Here, we show at the atomic level how inositol pyrophosphates interact with SPX domains of subunits Vtc2 and Vtc3 to control the activity of the VTC complex. Vtc2 inhibits the catalytically active VTC subunit Vtc4 by homotypic SPX-SPX interactions via the conserved helix α1 and the previously undescribed helix α7. Binding of inositol pyrophosphates to Vtc2 abrogates this interaction, thus activating the VTC complex. Accordingly, VTC activation is also achieved by site-specific point mutations that disrupt the SPX-SPX interface. Structural data suggest that ligand binding induces reorientation of helix α1 and exposes the modifiable helix α7, which might facilitate its post-translational modification in vivo. The variable composition of these regions within the SPX domain family might contribute to the diversified SPX functions in eukaryotic phosphate homeostasis.

The cytoplasmic synthesis and coupled membrane translocation of eukaryotic polyphosphate by signal-activated VTC complex

Inorganic polyphosphate (polyP) is an ancient energy metabolite and phosphate store that occurs ubiquitously in all organisms. The vacuolar transporter chaperone (VTC) complex integrates cytosolic polyP synthesis from ATP and polyP membrane translocation into the vacuolar lumen. In yeast and in other eukaryotes, polyP synthesis is regulated by inositol pyrophosphate (PP-InsP) nutrient messengers, directly sensed by the VTC complex. Here, we report the cryo-electron microscopy structure of signal-activated VTC complex at 3.0 Å resolution. Baker's yeast VTC subunits Vtc1, Vtc3, and Vtc4 assemble into a 3:1:1 complex. Fifteen trans-membrane helices form a novel membrane channel enabling the transport of newly synthesized polyP into the vacuolar lumen. PP-InsP binding orients the catalytic polymerase domain at the entrance of the trans-membrane channel, both activating the enzyme and coupling polyP synthesis and membrane translocation. Together with biochemical and cellular studies, our work provides mechanistic insights into the biogenesis of an ancient energy metabolite.

Inorganic polyphosphate abets silencing of a sub-telomeric gene cluster in fission yeast

Inorganic polyphosphate is a ubiquitous polymer with myriad roles in cell and organismal physiology. Whereas there is evidence for nuclear polyphosphate, its impact on transcriptional regulation in eukaryotes is unkown. Transcriptional profiling of fission yeast cells lacking polyphosphate (via deletion of the catalytic subunit Vtc4 of the Vtc4/Vtc2 polyphosphate polymerase complex) elicited de-repression of four protein-coding genes located within the right sub-telomeric arm of chromosome I that is known to be transcriptionally silenced by the TORC2 complex. These genes were equally de-repressed in vtc2 ∆ cells and in cells expressing polymerase-dead Vtc4, signifying that polyphosphate synthesis is required for repression of these sub-telomeric genes.

Disruption of phosphate metabolism and sterol transport-related genes conferring yeast resistance to vanillin and rapid ethanol production

Vanillin is a potent growth-inhibiting factor in Saccharomyces cerevisiae during lignocellulose biorefineries. Here, a haploid gene-deletion library was screened to search for vanillin-tolerant mutants and explain the possible tolerance mechanisms. Twenty-two deletion mutants were identified. The deleted genes in these mutants were involved in phosphate and inositol polyphosphate metabolism and intracellular sterol transport. Activation of the phosphate signaling pathway is not conducive to yeast against the pressure of vanillin. Furthermore, the findings indicate the role of inositol polyphosphates in altering vanillin tolerance by regulating phosphate metabolism. Meanwhile, reducing the transport of sterols from the plasma membrane enhanced tolerance to vanillin. In the presence of vanillin, the representative yeast deletions, pho84Δ and lam3Δ, showed good growth performance and promoted rapid ethanol production. Overall, this study identifies robust yeast strain alternatives for ethanol fermentation of cellulose and provides guidance for further genomic reconstruction of yeast strains.

PHM6 and PHM7 genes are essential for phosphate surplus in the cells of Saccharomyces cerevisiae

The cells of Saccharomyces cerevisiae are capable for phosphate surplus: the increased uptake of phosphate (Pi) and accumulation of inorganic polyphosphate (polyP) occur when the cells after Pi limitation were cultivated in a medium supplemented with Pi. We demonstrated that single knockout mutations in the PHO84, PHO87, and PHO89 genes encoding plasma membrane phosphate transporters suppressed the Pi uptake and polyP accumulation under phosphate surplus at nitrogen starvation. The knockout strains in the PHM6 and PHM7 genes encoding unannotated PHO-proteins showed decreased polyP accumulation under Pi surplus both at nitrogen starvation and in complete YPD medium. This is due to the suppression of Pi uptake in the cells of these mutant strains. We speculate that Pi transporters of plasma membrane, and Phm6 and Phm7 proteins function in concert providing increased Pi uptake at phosphate surplus conditions.

Inorganic Polyphosphate: Coacervate Formation and Functional Significance in Nanomedical Applications

Inorganic polyphosphates (polyP) are long-chain polymers of orthophosphate residues, which, depending on the external conditions, can be present both physiologically and synthetically in either soluble, nanoparticulate or coacervate form. In recent years, these polymers have received increasing attention due to their unprecedented ability to exhibit both morphogenetic and metabolic energy delivering properties. There are no other physiological molecules that contain as many metabolically utilizable, high-energy bonds as polyP, making these polymers of particular medical interest as components of advanced hydrogel scaffold materials for potential applications in ATP-dependent tissue regeneration and repair. However, these polymers show physiological activity only in soluble form and in the coacervate phase, but not as stable metal-polyP nanoparticles. Therefore, understanding the mechanisms of formation of polyP coacervates and nanoparticles as well as their transformations is important for the design of novel materials for tissue implants, wound healing, and drug delivery and is discussed here.

Structural and functional studies of Arabidopsis thaliana triphosphate tunnel metalloenzymes reveal roles for additional domains

Triphosphate tunnel metalloenzymes (TTMs) are found in all biological kingdoms and have been characterized in microorganisms and animals. Members of the TTM family have divergent biological functions and act on a range of triphosphorylated substrates (RNA, thiamine triphosphate, and inorganic polyphosphate). TTMs in plants have received considerably less attention and are unique in that some homologs harbor additional domains including a P-loop kinase and transmembrane domain. Here, we report on structural and functional aspects of the multimodular TTM1 and TTM2 of Arabidopsis thaliana. Our tissue and cellular microscopy studies show that both AtTTM1 and AtTTM2 are expressed in actively dividing (meristem) tissue and are tail-anchored proteins at the outer mitochondrial membrane, mediated by the single C-terminal transmembrane domain, supporting earlier studies. In addition, we reveal from crystal structures of AtTTM1 in the presence and absence of a nonhydrolyzable ATP analog a catalytically incompetent TTM tunnel domain tightly interacting with the P-loop kinase domain that is locked in an inactive conformation. Our structural comparison indicates that a helical hairpin may facilitate movement of the TTM domain, thereby activating the kinase. Furthermore, we conducted genetic studies to show that AtTTM2 is important for the developmental transition from the vegetative to the reproductive phase in Arabidopsis, whereas its closest paralog AtTTM1 is not. We demonstrate through rational design of mutations based on the 3D structure that both the P-loop kinase and TTM tunnel modules of AtTTM2 are required for the developmental switch. Together, our results provide insight into the structure and function of plant TTM domains.

Ddp1 Cooperates with Ppx1 to Counter a Stress Response Initiated by Nonvacuolar Polyphosphate

In diverse cells from bacterial to mammalian species, inorganic phosphate is stored in long chains called polyphosphate (polyP). These nearly universal polymers, ranging from three to thousands of phosphate moieties in length, are associated with molecular functions, including energy homeostasis, protein folding, and cell signaling. In many cell types, polyphosphate is concentrated in subcellular compartments or organelles. In the budding yeast Saccharomyces cerevisiae, polyP synthesis by the membrane-bound vacuolar transporter chaperone (VTC) complex is coupled to its translocation into the lumen of the vacuole, a lysosome-like organelle, where it is stored at high concentrations. In contrast, the ectopic expression of the bacterial polyphosphate kinase (PPK) results in the toxic accumulation of polyP outside the vacuole. In this study, we used label-free mass spectrometry to investigate the mechanisms underlying this toxicity. We find that PPK expression results in the activation of a stress response mediated in part by the Hog1 and Yak1 kinases and the Msn2/Msn4 transcription factors as well as by changes in protein kinase A (PKA) activity. This response is countered by the combined action of the Ddp1 and Ppx1 polyphosphatases that function together to counter polyP accumulation and downstream toxicity. In contrast, the ectopic expression of previously proposed mammalian polyphosphatases did not impact PPK-mediated toxicity in this model, suggesting either that these enzymes do not function directly as polyphosphatases in vivo or that they require cofactors unique to higher eukaryotes. Our work provides insight into why polyP accumulation outside lysosome-like organelles is toxic. Furthermore, it serves as a resource for exploring how polyP may impact conserved biological processes at a molecular level.

A rare natural lipid induces neuroglobin expression to prevent amyloid oligomers toxicity and retinal neurodegeneration

Most neurodegenerative diseases such as Alzheimer's disease are proteinopathies linked to the toxicity of amyloid oligomers. Treatments to delay or cure these diseases are lacking. Using budding yeast, we report that the natural lipid tripentadecanoin induces expression of the nitric oxide oxidoreductase Yhb1 to prevent the formation of protein aggregates during aging and extends replicative lifespan. In mammals, tripentadecanoin induces expression of the Yhb1 orthologue, neuroglobin, to protect neurons against amyloid toxicity. Tripentadecanoin also rescues photoreceptors in a mouse model of retinal degeneration and retinal ganglion cells in a Rhesus monkey model of optic atrophy. Together, we propose that tripentadecanoin affects p-bodies to induce neuroglobin expression and offers a potential treatment for proteinopathies and retinal neurodegeneration.

Blocking Polyphosphate Mobilization Inhibits Pho4 Activation and Virulence in the Pathogen Candida albicans

The ability of pathogenic fungi to obtain essential nutrients from the host is vital for virulence. In Candida albicans, acquisition of the macronutrient phosphate is regulated by the Pho4 transcription factor and is important for both virulence and resistance to host-encountered stresses. All cells store phosphate in the form of polyphosphate (polyP), a ubiquitous polymer comprising tens to hundreds of phosphate residues. Release of phosphate from polyP is one of the first responses evoked in response to phosphate starvation, and here, we sought to explore the importance of polyP mobilization in the pathobiology of C. albicans. We found that two polyphosphatases, Ppn1 and Ppx1, function redundantly to release phosphate from polyP in C. albicans. Strikingly, we reveal that blocking polyP mobilization prevents the activation of the Pho4 transcription factor: following P_i starvation, Pho4 fails to accumulate in the nucleus and induce P_i acquisition genes in ppn1Δ ppx1Δ cells. Consequently, ppn1Δ ppx1Δ cells display impaired resistance to the same range of stresses that require Pho4 for survival. In addition, cells lacking both polyphosphatases are exquisitely sensitive to DNA replication stress, indicating that polyP mobilization is needed to support the phosphate-demanding process of DNA replication. Blocking polyP mobilization also results in significant morphological defects, as ppn1Δ ppx1Δ cells form large pseudohypha-like cells that are resistant to serum-induced hypha formation. Thus, polyP mobilization impacts key processes important for the pathobiology of C. albicans, and consistent with this, we found that blocking this process attenuates the virulence of this important human fungal pathogen.

Impact of arsenic on phosphate solubilization, acquisition and poly-phosphate accumulation in endophytic fungus Serendipita indica

Symbiotic interactions play a crucial role in the phosphate (Pi) nutrient status of the host plant and offer resilience during biotic and abiotic stresses. Despite a competitive behavior of arsenic (AsV) with Pi, Serendipita indica association promotes plant growth by reducing arsenic bioavailability in the rhizosphere. Reduced arsenic availability is due to the adsorption, accumulation, and precipitation of arsenic in the fungus. The present investigation focused on the fitness and performance of Pi acquisition and utilization in S. indica for growth and metabolism under arsenic stress. The fungus accumulates a massive amount of arsenic up to 2459.3 ppm at a tolerable limit of arsenic supply (1 mM) with a bioaccumulation factor (BAF) 32. Arsenic induces Pi transporter expression to stimulate the arsenic acquisition in the fungus. At the same time, Pi accumulation was also enhanced by 112.2 times higher than the control with an increase in poly-P (polyphosphate) content (6.69 times) of the cell. This result suggests arsenic does not hamper poly-P storage in the cell but shows a marked delocalization of stored poly-P from the vacuoles. Furthermore, an enhanced exopolyphosphatase activity and poly-P storage during arsenic stress suggest induction of cellular machinery for the utilization of Pi is required to deal with arsenic toxicity and competition. However, at high arsenic supply (2.5 and 5 mM), 14.55 and 22.07 times reduced Pi utilization, respectively, was observed during the Pi uptake by the fungus. The reduction of Pi uptake reduces the cell growth and biomass due to competition between arsenic and phosphate. The study suggests no negative impact of arsenic on the Pi acquisition, storage, and metabolism in symbiotic fungus, S. indica, under environmental arsenic contamination.

Inorganic Polymeric Materials for Injured Tissue Repair: Biocatalytic Formation and Exploitation

Two biocatalytically produced inorganic biomaterials show great potential for use in regenerative medicine but also other medical applications: bio-silica and bio-polyphosphate (bio-polyP or polyP). Biosilica is synthesized by a group of enzymes called silicateins, which mediate the formation of amorphous hydrated silica from monomeric precursors. The polymeric silicic acid formed by these enzymes, which have been cloned from various siliceous sponge species, then undergoes a maturation process to form a solid biosilica material. The second biomaterial, polyP, has the extraordinary property that it not only has morphogenetic activity similar to biosilica, i.e., can induce cell differentiation through specific gene expression, but also provides metabolic energy through enzymatic cleavage of its high-energy phosphoanhydride bonds. This reaction is catalyzed by alkaline phosphatase, a ubiquitous enzyme that, in combination with adenylate kinase, forms adenosine triphosphate (ATP) from polyP. This article attempts to highlight the biomedical importance of the inorganic polymeric materials biosilica and polyP as well as the enzymes silicatein and alkaline phosphatase, which are involved in their metabolism or mediate their biological activity.

Plant phosphate nutrition: sensing the stress

Phosphorus (P) is obtained by plants as phosphate (Pi) from the soil and low Pi levels affects plant growth and development. Adaptation to low Pi condition entails sensing internal and external Pi levels and translating those signals to molecular and morphophysiological changes in the plant. In this review, we present findings related to local and systemin Pi sensing with focus the molecular mechanisms behind root system architectural changes and the impact of hormones and epigenetic mechanisms affecting those changes. We also present some of the recent advances in the Pi sensing and signaling mechanisms focusing on inositol pyrophosphate InsP8 and its interaction with SPX domain proteins to regulate the activity of the central regulator of the Pi starvation response, PHR.

Cleavage-Polyadenylation Factor Cft1 and SPX Domain Proteins Are Agents of Inositol Pyrophosphate Toxicosis in Fission Yeast

Inositol pyrophosphate (IPP) dynamics govern expression of the fission yeast phosphate homeostasis regulon via their effects on lncRNA-mediated transcription interference. The growth defects (ranging from sickness to lethality) elicited by fission yeast mutations that inactivate IPP pyrophosphatase enzymes are exerted via the agonistic effects of too much 1,5-IP8 on RNA 3'-processing and transcription termination. To illuminate determinants of IPP toxicosis, we conducted a genetic screen for spontaneous mutations that suppressed the sickness of Asp1 pyrophosphatase mutants. We identified a missense mutation, C823R, in the essential Cft1 subunit of the cleavage and polyadenylation factor complex that suppresses even lethal Asp1 IPP pyrophosphatase mutations, thereby fortifying the case for 3'-processing/termination as the target of IPP toxicity. The suppressor screen also identified Gde1 and Spx1 (SPAC6B12.07c), both of which have an IPP-binding SPX domain and both of which are required for lethality elicited by Asp1 mutations. A survey of other SPX proteins in the proteome identified the Vtc4 and Vtc2 subunits of the vacuolar polyphosphate polymerase as additional agents of IPP toxicosis. Gde1, Spx1, and Vtc4 contain enzymatic modules (glycerophosphodiesterase, RING finger ubiquitin ligase, and polyphosphate polymerase, respectively) fused to their IPP-sensing SPX domains. Structure-guided mutagenesis of the IPP-binding sites and the catalytic domains of Gde1 and Spx1 indicated that both modules are necessary to elicit IPP toxicity. Whereas Vtc4 polymerase catalytic activity is required for IPP toxicity, its IPP-binding site is not. Epistasis analysis, transcriptome profiling, and assays of Pho1 expression implicate Spx1 as a transducer of IP8 signaling to the 3'-processing/transcription termination machinery. IMPORTANCE Impeding the catabolism of the inositol pyrophosphate (IPP) signaling molecule IP8 is cytotoxic to fission yeast. Here, by performing a genetic suppressor screen, we identified several cellular proteins required for IPP toxicosis. Alleviation of IPP lethality by a missense mutation in the essential Cft1 subunit of the cleavage and polyadenylation factor consolidates previous evidence that toxicity results from IP8 action as an agonist of RNA 3'-processing and transcription termination. Novel findings are that IP8 toxicity depends on IPP-sensing SPX domain proteins with associated enzymatic functions: Gde1 (glycerophosphodiesterase), Spx1 (ubiquitin ligase), and Vtc2/4 (polyphosphate polymerase). The effects of Spx1 deletion on phosphate homeostasis imply a role for Spx1 in communicating an IP8-driven signal to the transcription and RNA processing apparatus.