How versatile are inositol phosphate kinases?
Ontology highlight
ABSTRACT:
SUBMITTER: Shears SB
PROVIDER: S-EPMC1223885 | biostudies-other | 2004 Jan
REPOSITORIES: biostudies-other
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Project description:Inositol phosphate encompasses a large multifaceted family of signalling molecules that originate from the combinatorial attachment of phosphate groups to the inositol ring. To date, four distinct inositol kinases have been identified, namely, IPK, ITPK, IPPK (IP5-2K), and PPIP5K. Although, ITPKs have recently been identified in archaea, eukaryotes have taken advantage of these enzymes to create a sophisticated signalling network based on inositol phosphates. However, it remains largely elusive what fundamental biochemical principles control the signalling cascade. Here, we present an evolutionary approach to understand the development of the 'inositol phosphate code' in eukaryotes. Distribution analyses of these four inositol kinase groups throughout the eukaryotic landscape reveal the loss of either ITPK, or of PPIP5K proteins in several species. Surprisingly, the loss of IPPK, an enzyme thought to catalyse the rate limiting step of IP6 (phytic acid) synthesis, was also recorded. Furthermore, this study highlights a noteworthy difference between animal (metazoan) and plant (archaeplastida) lineages. While metazoan appears to have a substantial amplification of IPK enzymes, archaeplastida genomes show a considerable increase in ITPK members. Differential evolution of IPK and ITPK between plant and animal lineage is likely reflective of converging functional adaptation of these two types of inositol kinases. Since, the IPK family comprises three sub-types IPMK, IP6K, and IP3-3K each with dedicated enzymatic specificity in metazoan, we propose that the amplified ITPK group in plant could be classified in sub-types with distinct enzymology.
| S-EPMC8024741 | biostudies-literature
Project description:Many eukaryotic proteins regulating phosphate (Pi) homeostasis contain SPX domains that are receptors for inositol pyrophosphates (PP-InsP), suggesting that PP-InsPs may regulate Pi homeostasis. Here we report that deletion of two diphosphoinositol pentakisphosphate kinases VIH1/2 impairs plant growth and leads to constitutive Pi starvation responses. Deletion of phosphate starvation response transcription factors partially rescues vih1 vih2 mutant phenotypes, placing diphosphoinositol pentakisphosphate kinases in plant Pi signal transduction cascades. VIH1/2 are bifunctional enzymes able to generate and break-down PP-InsPs. Mutations in the kinase active site lead to increased Pi levels and constitutive Pi starvation responses. ATP levels change significantly in different Pi growth conditions. ATP-Mg2+ concentrations shift the relative kinase and phosphatase activities of diphosphoinositol pentakisphosphate kinases in vitro. Pi inhibits the phosphatase activity of the enzyme. Thus, VIH1 and VIH2 relay changes in cellular ATP and Pi concentrations to changes in PP-InsP levels, allowing plants to maintain sufficient Pi levels.
| S-EPMC6731061 | biostudies-literature
Project description:Phosphate's central role in most biochemical reactions in a living organism requires carefully maintained homeostasis. Although phosphate homeostasis in mammals has long been studied at the organismal level, the intracellular mechanisms controlling phosphate metabolism are not well-understood. Inositol pyrophosphates have emerged as important regulatory elements controlling yeast phosphate homeostasis. To verify whether inositol pyrophosphates also regulate mammalian cellular phosphate homeostasis, here we knocked out inositol hexakisphosphate kinase (IP6K) 1 and IP6K2 to generate human HCT116 cells devoid of any inositol pyrophosphates. Using PAGE and HPLC analysis, we observed that the IP6K1/2-knockout cells have nondetectable levels of the IP6-derived IP7 and IP8 and also exhibit reduced synthesis of the IP5-derived PP-IP4 Nucleotide analysis showed that the knockout cells contain increased amounts of ATP, whereas the Malachite green assay found elevated levels of free intracellular phosphate. Furthermore, [32Pi] pulse labeling experiments uncovered alterations in phosphate flux, with both import and export of phosphate being decreased in the knockout cells. Functional analysis of the phosphate exporter xenotropic and polytropic retrovirus receptor 1 (XPR1) revealed that it is regulated by inositol pyrophosphates, which can bind to its SPX domain. We conclude that IP6K1 and -2 together control inositol pyrophosphate metabolism and thereby physiologically regulate phosphate export and other aspects of mammalian cellular phosphate homeostasis.
| S-EPMC6663863 | biostudies-literature
Project description:The pathway for the synthesis of di-myo-inositol-phosphate (DIP) was recently elucidated on the basis of the detection of the relevant activities in cell extracts of Archaeoglobus fulgidus and structural characterization of products by nuclear magnetic resonance (NMR) (N. Borges, L. G. Gonçalves, M. V. Rodrigues, F. Siopa, R. Ventura, C. Maycock, P. Lamosa, and H. Santos, J. Bacteriol. 188:8128-8135, 2006). Here, a genomic approach was used to identify the genes involved in the synthesis of DIP. Cloning and expression in Escherichia coli of the putative genes for CTP:l-myo-inositol-1-phosphate cytidylyltransferase and DIPP (di-myo-inositol-1,3'-phosphate-1'-phosphate, a phosphorylated form of DIP) synthase from several (hyper)thermophiles (A. fulgidus, Pyrococcus furiosus, Thermococcus kodakaraensis, Aquifex aeolicus, and Rubrobacter xylanophilus) confirmed the presence of those activities in the gene products. The DIPP synthase activity was part of a bifunctional enzyme that catalyzed the condensation of CTP and l-myo-inositol-1-phosphate into CDP-l-myo-inositol, as well as the synthesis of DIPP from CDP-l-myo-inositol and l-myo-inositol-1-phosphate. The cytidylyltransferase was absolutely specific for CTP and l-myo-inositol-1-P; the DIPP synthase domain used only l-myo-inositol-1-phosphate as an alcohol acceptor, but CDP-glycerol, as well as CDP-l-myo-inositol and CDP-d-myo-inositol, were recognized as alcohol donors. Genome analysis showed homologous genes in all organisms known to accumulate DIP and for which genome sequences were available. In most cases, the two activities (l-myo-inositol-1-P cytidylyltransferase and DIPP synthase) were fused in a single gene product, but separate genes were predicted in Aeropyrum pernix, Thermotoga maritima, and Hyperthermus butylicus. Additionally, using l-myo-inositol-1-phosphate labeled on C-1 with carbon 13, the stereochemical configuration of all the metabolites involved in DIP synthesis was established by NMR analysis. The two inositol moieties in DIP had different stereochemical configurations, in contradiction of previous reports. The use of the designation di-myo-inositol-1,3'-phosphate is recommended to facilitate tracing individual carbon atoms through metabolic pathways.
| S-EPMC1951816 | biostudies-literature
Project description:Human inositol phosphate multikinase (HsIPMK) critically contributes to intracellular signaling through its inositol-1,4,5-trisphosphate (Ins(1,4,5)P3) 3-kinase and phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) 3-kinase activities. This catalytic profile is not conserved; orthologs from Arabidopsis thaliana and Saccharomyces cerevisiae are predominantly Ins(1,4,5)P3 6-kinases, and the plant enzyme cannot phosphorylate PtdIns(4,5)P2 Therefore, crystallographic analysis of the yeast and plant enzymes, without bound inositol phosphates, do not structurally rationalize HsIPMK activities. Here, we present 1.6-Å resolution crystal structures of HsIPMK in complex with either Ins(1,4,5)P3 or PtdIns(4,5)P2 The Ins(1,4,5)P3 headgroup of PtdIns(4,5)P2 binds in precisely the same orientation as free Ins(1,4,5)P3 itself, indicative of evolutionary optimization of 3-kinase activities against both substrates. We report on nucleotide binding between the separate N- and C-lobes of HsIPMK. The N-lobe exhibits a remarkable degree of conservation with protein kinase A (root mean square deviation = 1.8 Å), indicating common ancestry. We also describe structural features unique to HsIPMK. First, we observed a constrained, horseshoe-shaped substrate pocket, formed from an ?-helix, a 310 helix, and a recently evolved tri-proline loop. We further found HsIPMK activities rely on a preponderance of Gln residues, in contrast to the larger Lys and Arg residues in yeast and plant orthologs. These conclusions are supported by analyzing 14 single-site HsIPMK mutants, some of which differentially affect 3-kinase and 6-kinase activities. Overall, we structurally rationalize phosphorylation of Ins(1,4,5)P3 and PtdIns(4,5)P2 by HsIPMK.
| S-EPMC5672042 | biostudies-literature
Project description:Opportunistic fungi are a major cause of morbidity and mortality world-wide, particularly in immunocompromised individuals. Developing new treatments to combat invasive fungal disease is challenging given that fungal and mammalian host cells are eukaryotic, with similar organization and physiology. Even therapies targeting unique fungal cell features have limitations and drug resistance is emerging. New approaches to the development of antifungal drugs are therefore needed urgently. Cryptococcus neoformans, the commonest cause of fungal meningitis worldwide, is an accepted model for studying fungal pathogenicity and driving drug discovery. We recently characterized a phospholipase C (Plc1)-dependent pathway in C. neoformans comprising of sequentially-acting inositol polyphosphate kinases (IPK), which are involved in synthesizing inositol polyphosphates (IP). We also showed that the pathway is essential for fungal cellular function and pathogenicity. The IP products of the pathway are structurally diverse, each consisting of an inositol ring, with phosphate (P) and pyrophosphate (PP) groups covalently attached at different positions. This review focuses on (1) the characterization of the Plc1/IPK pathway in C. neoformans; (2) the identification of PP-IP₅ (IP₇) as the most crucial IP species for fungal fitness and virulence in a mouse model of fungal infection; and (3) why IPK enzymes represent suitable candidates for drug development.
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Project description:The plant glycogen synthase kinase 3 (GSK3)-like kinases are highly conserved protein serine/threonine kinases that are grouped into four subfamilies. Similar to their mammalian homologs, these kinases are constitutively active under normal growth conditions but become inactivated in response to diverse developmental and environmental signals. Since their initial discoveries in the early 1990s, many biochemical and genetic studies were performed to investigate their physiological functions in various plant species. These studies have demonstrated that the plant GSK3-like kinases are multifunctional kinases involved not only in a wide variety of plant growth and developmental processes but also in diverse plant stress responses. Here we summarize our current understanding of the versatile physiological functions of the plant GSK3-like kinases along with their confirmed and potential substrates.
| S-EPMC8151121 | biostudies-literature
Project description:myo-Inositol-3-phosphate synthase (MIPS) plays a crucial role in inositol homeostasis. Transcription of the coding gene INO1 is highly regulated. However, regulation of the enzyme is not well defined. We previously showed that MIPS is indirectly inhibited by valproate, suggesting that the enzyme is post-translationally regulated. Using (32)Pi labeling and phosphoamino acid analysis, we show that yeast MIPS is a phosphoprotein. Mass spectrometry analysis identified five phosphosites, three of which are conserved in the human MIPS. Analysis of phosphorylation-deficient and phosphomimetic site mutants indicated that the three conserved sites in yeast (Ser-184, Ser-296, and Ser-374) and humans (Ser-177, Ser-279, and Ser-357) affect MIPS activity. Both S296A and S296D yeast mutants and S177A and S177D human mutants exhibited decreased enzymatic activity, suggesting that a serine residue is critical at that location. The phosphomimetic mutations S184D (human S279D) and S374D (human S357D) but not the phosphodeficient mutations decreased activity, suggesting that phosphorylation of these two sites is inhibitory. The double mutation S184A/S374A caused an increase in MIPS activity, conferred a growth advantage, and partially rescued sensitivity to valproate. Our findings identify a novel mechanism of regulation of inositol synthesis by phosphorylation of MIPS.
| S-EPMC3772229 | biostudies-literature
Project description:Diphosphoinositol phosphates (PP-InsPs) are inositol phosphates (InsPs) that contain PP (diphosphate) groups. Converting a phosphate group in an InsP into a diphosphate has been reported to enhance affinity for some binding proteins. We synthesised 1-PP-Ins(4,5)P2, the first diphosphate analogue of the intracellular signalling molecule InsP3, and examined its effects on InsP3 receptors, which are intracellular Ca2+ channels. 1-PP-Ins(4,5)P2 was indistinguishable from InsP3 in its ability to bind to and activate type 1 InsP3 receptors, indicating that the diphosphate modification of InsP3 affected neither affinity nor efficacy. Nevertheless, 1-PP-Ins(4,5)P2 is the most potent 1-phosphate modified analogue of InsP3 yet identified. PP-InsPs are generally hydrolysed by diphosphoinositol phosphate phosphohydrolases (DIPPs), but 1-PP-Ins(4,5)P2 was not readily metabolised by human DIPPs. Differential scanning fluorimetry showed that 1-PP-Ins(4,5)P2 stabilises DIPP proteins, but to a lesser extent than naturally occurring substrates 1-PP-InsP5 and 5-PP-InsP5. The non-hydrolysable InsP7 analogues 1-PCP-InsP5 and 5-PCP-InsP5 showed comparable stabilising abilities to their natural counterparts and may therefore be promising substrate analogues for co-crystallisation with DIPPs.
| S-EPMC6071853 | biostudies-literature
Project description:Many Archaea and Bacteria isolated from hot, marine environments accumulate di-myo-inositol-phosphate (DIP), primarily in response to heat stress. The biosynthesis of this compatible solute involves the activation of inositol to CDP-inositol via the action of a recently discovered CTP:inositol-1-phosphate cytidylyltransferase (IPCT) activity. In most cases, IPCT is part of a bifunctional enzyme comprising two domains: a cytoplasmic domain with IPCT activity and a membrane domain catalyzing the synthesis of di-myo-inositol-1,3'-phosphate-1'-phosphate from CDP-inositol and L-myo-inositol phosphate. Herein, we describe the first X-ray structure of the IPCT domain of the bifunctional enzyme from the hyperthermophilic archaeon Archaeoglobus fulgidus DSMZ 7324. The structure of the enzyme in the apo form was solved to a 1.9-Å resolution. The enzyme exhibited apparent K(m) values of 0.9 and 0.6 mM for inositol-1-phosphate and CTP, respectively. The optimal temperature for catalysis was in the range 90 to 95°C, and the V(max) determined at 90°C was 62.9 ?mol · min(-1) · mg of protein(-1). The structure of IPCT is composed of a central seven-stranded mixed ?-sheet, of which six ?-strands are parallel, surrounded by six ?-helices, a fold reminiscent of the dinucleotide-binding Rossmann fold. The enzyme shares structural homology with other pyrophosphorylases showing the canonical motif G-X-G-T-(R/S)-X(4)-P-K. CTP, L-myo-inositol-1-phosphate, and CDP-inositol were docked into the catalytic site, which provided insights into the binding mode and high specificity of the enzyme for CTP. This work is an important step toward the final goal of understanding the full catalytic route for DIP synthesis in the native, bifunctional enzyme.
| S-EPMC3133074 | biostudies-literature