The Effect of Phosphorus Metabolism on the Motion of Saccharomyces cerevisiae Volutin Granules

It is known that moving volutin granules (“dancing bodies”), mechanism of which occurrence remains poorly understood, can be observed in yeast vacuoles. This study was performed to reveal the presence of a connection between moving volutin granules of Saccharomyces cerevisiae and polyphosphate metabolism in conditions of phosphoric starvation and hypercompensation. Methods. Cytological, biochemical, statistical methods were used in the study. Results. It was observed that the inactivation of the PPN1 gene, which encodes exopolyphosphatase Ppn1, resulted in a change in the number of cells with moving volutin granules (“dancing bodies” index) in the studied conditions. The index of “dancing bodies” was almost always lower in mutant CRN strain than in parent CRY strain. Using linear correlation analysis and factor analysis with the method of principal component, it was established that the “dancing bodies” index in both strains had significant correlation coefficients with exopolyphosphatase activity (EPPA) and the content of polyphosphate fractions (polyP). The difference was that this index in parent strain correlated better with the first three fractions of inorganic polyphosphates, while in mutant strain – with polyP4 and EPPA. Conclusions. Obtained data indicated the direct connection of motion of volutin granules with phosphoric metabolism in the studied conditions. It is assumed that the phenomenon of “dancing bodies” may be a consequence of the activity of vacuolar polyphosphatases.

Identification and enzymatic analysis of an archaeal ATP-dependent serine kinase from the hyperthermophilic archaeon Staphylothermus marinus

Serine kinase catalyzes the phosphorylation of free serine (Ser) to produce O -phosphoserine (Sep). An ADP-dependent Ser kinase in the hyperthermophilic archaeon Thermococcus kodakarensis ( Tk -SerK) is involved in cysteine (Cys) biosynthesis and most likely Ser assimilation. An ATP-dependent Ser kinase in the mesophilic bacterium Staphylococcus aureus is involved in siderophore biosynthesis. Although proteins displaying various degrees of similarity with Tk -SerK are distributed in a wide range of organisms, it is unclear if they are actually Ser kinases. Here we examined proteins from Desulfurococcales species in Crenarchaeota that display moderate similarity with Tk -SerK from Euryarchaeota (42-45% identical). Tk - serK homologs from Staphylothermus marinus (Smar_0555), Desulfurococcus amylolyticus (DKAM_0858), and Desulfurococcus mucosus (Desmu_0904) were expressed in Escherichia coli . All three partially purified recombinant proteins exhibited Ser kinase activity utilizing ATP rather than ADP as a phosphate donor. Purified Smar_0555 protein displayed activity towards l -Ser, but not with other compounds including d -Ser, l -threonine and l -homoserine. The enzyme utilized ATP, UTP, GTP, CTP, and the inorganic polyphosphates triphosphate and tetraphosphate as the phosphate donor. Kinetic analysis indicated that the Smar_0555 protein preferred nucleoside 5’-triphosphates compared to triphosphate as a phosphate donor. Transcript levels and Ser kinase activity in S. marinus cells grown with or without serine suggested that the Smar_0555 gene is constitutively expressed. The genes encoding Ser kinases examined here form an operon with genes most likely responsible for the conversion between Sep and 3-phosphoglycerate of central sugar metabolism, suggesting that the ATP-dependent Ser kinases from Desulfurococcales play a role in the assimilation of Ser. IMPORTANCE Homologs of the ADP-dependent Ser kinase from the archaeon Thermococcus kodakarensis ( Tk -SerK) include representatives from all three domains of life. The results of this study show that even homologs from the archaeal order Desulfurococcales, which are the most structurally related to the ADP-dependent Ser kinases from the Thermococcales, are Ser kinases that utilize ATP, and in at least some cases inorganic polyphosphates, as the phosphate donor. The differences in properties between the Desulfurococcales and Thermococcales enzymes raise the possibility that Tk -SerK homologs constitute a group of kinases that phosphorylate free serine with a wide range of phosphate donors.

Long-chain polyphosphates impair SARS-CoV-2 infection and replication: a route for therapy in man

Anti-viral activities of long-chain inorganic polyphosphates (PolyPs) against severe acute respiratory syndrome coronavirus (SARS-CoV)-2 infection were investigated. In molecular docking analyses, PolyPs interacted with several conserved angiotensin-converting enzyme (ACE)2 and RNA-dependent RNA polymerase (RdRp) amino acids. We thus tested PolyPs for functional interactions in vitro in SARS-CoV-2–infected Vero E6, Caco2 and human primary nasal epithelial cells. Immunofluorescence, qPCR, direct RNA sequencing, FISH and Immunoblotting were used to determine virus loads and transcription levels of genomic(g)RNAs and sub-genomic(sg)RNAs. We show that PolyP120 binds to ACE2 and enhances its proteasomal degradation. PolyP120 shows steric hindrance of the genomic Sars-CoV-2-RNA/RdRP complex, to impair synthesis of positive-sense gRNAs, viral subgenomic transcripts and structural proteins needed for viral replication. Thus, PolyP120 impairs infection and replication of Korean and European (containing non-synonymous variants) SARS-CoV-2 strains. As PolyPs have no toxic activities, we envision their use as a nebulised formula for oropharyngeal delivery to prevent infections of SARS-CoV-2 and during early phases of antiviral therapy.

A genetically validated approach to detect inorganic polyphosphates in plants

Inorganic polyphosphates (polyPs) are linear polymers of orthophosphate units linked by phosphoanhydride bonds. PolyPs represent important stores of phosphate and energy, and are abundantly found in many pro- and eukaryotic organisms. In plants, the existence of polyPs has been established using microscopy and biochemical extraction methods that are now known to produce artifacts. Here we use a polyP-specific dye and a polyP binding domain to detect polyPs in plant and algal cells. To develop the staining protocol, we induced polyP granules inNicotiana benthamianaand Arabiopsis cells by heterologous expression ofE. colipolyphosphate kinase 1 (PPK1). Over-expression of PPK1 but not of a catalytically impaired version of the enzyme lead to severe growth phenotypes, suggesting that ATP-dependent synthesis and accumulation of polyPs in the plant cytosol is toxic. We next crossed stable PPK1 expressing Arabidopsis lines with plants expressing the polyP-binding domain ofE. coliexopolyphosphatase (PPX1c), which co-localized with PPK1-generated polyP granules. These granules were stained by the polyP-specific dye JC-D7 and appeared as electron dense structures in transmission electron microscopy (TEM) sections. Using the polyP staining protocol derived from these experiments, we screened for polyP stores in different organs and tissues of both mono- and dicotyledonous plants. While we could not detect polyP granules in higher plants, we could visualize the polyP-rich acidocalicisomes in the green algaeChlamydomonas reinhardtii.Together, our experiments suggest that higher plants may not contain large polyPs stores.Significance StatementA chemical dye and an inorganic polyphosphate binding domain are shown to specifically label inorganic polyphosphate granules in transgenic Arabidopsis lines and Chlamydomonas acidocalcisomes. Using these tools, we show that in contrast to many prokaryotic and eukaryotic organisms, higher plants do not seem to contain large inorganic polyphosphate stores.