Assessing the omnipotence of inositol hexakisphosphate

Human plasma inositol hexakisphosphate (InsP 6 ) phosphatase identified as the Multiple Inositol Polyphosphate Phosphatase 1 (MINPP1)

Inositol hexakisphosphate (InsP 6 ), also known as phytic acid, is a potent chelator of bivalent cations. Intracellular InsP 6 molecules are associated with magnesium. Calcium is the prevalent bivalent cation outside the cell and its association with InsP 6 could lead to the formation of insoluble complexes. To avoid the formation of dangerous InsP 6 /Calcium precipitates in the bloodstream, mammals must possess a robust InsP 6 phosphatase in their plasma. Here we identify the Multiple Inositol Polyphosphate Phosphatase 1 ( MINPP1 ) as the InsP 6 phosphatase present in human plasma.

Inositol Hexaphosphate as an Inhibitor and Potential Regulator of p47phox Membrane Anchoring

As a key component for NADPH oxidase 2 (NOX2) activation, the peripheral membrane protein p47phox translocates a cytosolic activating complex to the membrane through its PX domain. This study elucidates a potential regulatory mechanism of p47phox recruitment and NOX2 activation by inositol hexaphosphate (IP6). Through NMR, fluorescence polarization, and FRET experimental results, IP6 is shown to be capable of breaking the lipid binding and membrane anchoring events of p47phox-PX with low micromolar potency. Other phosphorylated inositol species such as IP5(1,3,4,5,6), IP4(1,3,4,5), and IP3(1,3,4) show weaker binding and no ability to inhibit lipid interactions in physiological concentration ranges. The low micromolar potency of IP6 inhibition of the p47phox membrane anchoring suggests that physiologically relevant concentrations of IP6 serve as regulators, as seen in other membrane anchoring domains. The PX domain of p47phox is known to be promiscuous to a variety of phosphatidylinositol phosphate (PIP) lipids, and this regulation may help target the domain only to the membranes most highly enriched with the highest affinity PIPs, such as the phagosomal membrane, while preventing aberrant binding to other membranes with high and heterogeneous PIP content, such as the plasma membrane. This study provides insight into a potential novel regulatory mechanism behind NOX2 activation and reveals a role for small-molecule regulation in this important NOX2 activator.

Insights into the roles of inositol hexakisphosphate kinase 1 (IP6K1) in mammalian cellular processes

Inositol phosphates and their metabolites play a significant role in several biochemical pathways, gene expression regulation, and phosphate homeostasis. Among the different inositol phosphates, inositol hexakisphosphate (IP6) is a substrate of inositol hexakisphosphate kinases (IP6Ks), which phosphorylate one or more of the IP6 phosphate groups. Pyrophosphorylation of IP6 leads to the formation of inositol pyrophosphates, high-energy signaling molecules that mediate physiological processes through their ability to modify target protein activities, either by directly binding to their target protein or by pyrophosphorylating protein serine residues. 5-diphosphoinositol pentakisphosphate, the most abundant inositol pyrophosphate in mammals, has been extensively studied and found to be significantly involved in a wide range of physiological processes. Three IP6K (IP6K1, IP6K2, and IP6K3) isoforms regulate IP7 synthesis in mammals. Here, we summarize our current understanding of IP6K1's roles in cytoskeletal remodeling, trafficking, cellular migration, metabolism, gene expression, DNA repair, and immunity. We also briefly discuss current gaps in knowledge, highlighting the need for further investigation.

The yeast AMP-activated protein kinase Snf1 phosphorylates the inositol polyphosphate kinase Kcs1

The yeast Snf1/AMP-activated kinase (AMPK) maintains energy homeostasis, controlling metabolic processes and glucose derepression in response to nutrient levels and environmental cues. Under conditions of nitrogen or glucose limitation, Snf1 regulates pseudohyphal growth, a morphological transition characterized by the formation of extended multicellular filaments. During pseudohyphal growth, Snf1 is required for wild-type levels of inositol polyphosphate (InsP), soluble phosphorylated species of the six-carbon cyclitol inositol that function as conserved metabolic second messengers. InsP levels are established through the activity of a family of inositol kinases, including the yeast inositol polyphosphate kinase Kcs1, which principally generates pyrophosphorylated InsP7. Here, we report that Snf1 regulates Kcs1, affecting Kcs1 phosphorylation and inositol kinase activity. A snf1 kinase-defective mutant exhibits decreased Kcs1 phosphorylation, and Kcs1 is phosphorylated in vivo at Ser residues 537 and 646 during pseudohyphal growth. By in vitro analysis, Snf1 directly phosphorylates Kcs1, predominantly at amino acids 537 and 646. A yeast strain carrying kcs1 encoding Ser-to-Ala point mutations at these residues (kcs1-S537A,S646A) shows elevated levels of pyrophosphorylated InsP7, comparable to InsP7 levels observed upon deletion of SNF1. The kcs1-S537A,S646A mutant exhibits decreased pseudohyphal growth, invasive growth, and cell elongation. Transcriptional profiling indicates extensive perturbation of metabolic pathways in kcs1-S537A,S646A. Growth of kcs1-S537A,S646A is affected on medium containing sucrose and antimycin A, consistent with decreased Snf1p signaling. This work identifies Snf1 phosphorylation of Kcs1, collectively highlighting the interconnectedness of AMPK activity and InsP signaling in coordinating nutrient availability, energy homoeostasis, and cell growth.

Monitoring Intracellular IP6 with a Genetically Encoded Fluorescence Biosensor

Inositol hexakisphosphate (IP6), a naturally occurring metabolite of inositol with specific functions in different organelles or tissues, participates in numerous physiological processes and plays a key role in mammalian metabolic regulation. However, current IP6 detection methods, i.e., high-performance liquid chromatography and gel electrophoresis, require sample destruction and lack spatiotemporal resolution. Here, we construct and characterize a genetically encoded fluorescence biosensor named HIPSer that enables ratiometric quantitative IP6 detection in HEK293T cells and subcellular compartments. We demonstrate that HIPSer has a high sensitivity and relative selectivity for IP6 in vitro. We also provide proof-of-concept evidence that HIPSer can monitor IP6 levels in real time in HEK293T cells and can be targeted for IP6 detection in the nucleus of HEK293T cells. Moreover, HIPSer could also detect changes in IP6 content induced by chemical inhibition of IP6-metabolizing enzymes in HEK293T cells. Thus, HIPSer achieves spatiotemporally precise detection of fluctuations in endogenous IP6 in live cells and provides a versatile tool for mechanistic investigations of inositol phosphate functions in metabolism and signaling.

GPCR targeting of E3 ubiquitin ligase MDM2 by inactive β-arrestin

E3 ubiquitin ligase Mdm2 facilitates β-arrestin ubiquitination, leading to the internalization of G protein-coupled receptors (GPCRs). In this process, β-arrestins bind to Mdm2 and recruit it to the receptor; however, the molecular architecture of the β-arrestin-Mdm2 complex has not been elucidated yet. Here, we identified the β-arrestin-binding region (ABR) on Mdm2 and solved the crystal structure of β-arrestin1 in complex with Mdm2ABR peptide. The acidic residues of Mdm2ABR bind to the positively charged concave side of the β-arrestin1 N-domain. The C-tail of β-arrestin1 is still bound to the N-domain, indicating that Mdm2 binds to the inactive state of β-arrestin1, whereas the phosphorylated C-terminal tail of GPCRs binds to activate β-arrestins. The overlapped binding site of Mdm2 and GPCR C-tails on β-arrestin1 suggests that the binding of GPCR C-tails might trigger the release of Mdm2. Moreover, hydrogen/deuterium exchange experiments further show that Mdm2ABR binding to β-arrestin1 induces the interdomain interface to be more dynamic and uncouples the IP6-induced oligomer of β-arrestin1. These results show how the E3 ligase, Mdm2, interacts with β-arrestins to promote the internalization of GPCRs.

Cellular and Molecular Activities of IP6 in Disease Prevention and Therapy

IP6 (phytic acid) is a naturally occurring compound in plant seeds and grains. It is a poly-phosphorylated inositol derivative that has been shown to exhibit many biological activities that accrue benefits in health and diseases (cancer, diabetes, renal lithiasis, cardiovascular diseases, etc.). IP6 has been shown to have several cellular and molecular activities associated with its potential role in disease prevention. These activities include anti-oxidant properties, chelation of metal ions, inhibition of inflammation, modulation of cell signaling pathways, and modulation of the activities of enzymes and hormones that are involved in carbohydrate and lipid metabolism. Studies have shown that IP6 has anti-oxidant properties and can scavenge free radicals known to cause cellular damage and contribute to the development of chronic diseases such as cancers and cardiovascular diseases, as well as diabetes mellitus. It has also been shown to possess anti-inflammatory properties that may modulate immune responses geared towards the prevention of inflammatory conditions. Moreover, IP6 exhibits anti-cancer properties through the induction of cell cycle arrest, promoting apoptosis and inhibiting cancer cell growth. Additionally, it has been shown to have anti-mutagenic properties, which reduce the risk of malignancies by preventing DNA damage and mutations. IP6 has also been reported to have a potential role in bone health. It inhibits bone resorption and promotes bone formation, which may help in the prevention of bone diseases such as osteoporosis. Overall, IP6's cellular and molecular activities make it a promising candidate for disease prevention. As reported in many studies, its anti-inflammatory, anti-oxidant, and anti-cancer properties support its inclusion as a dietary supplement that may protect against the development of chronic diseases. However, further studies are needed to understand the mechanisms of action of this dynamic molecule and its derivatives and determine the optimal doses and appropriate delivery methods for effective therapeutic use.

One Scaffold, Two Conformations: The Ring-Flip of the Messenger InsP8 Occurs under Cytosolic Conditions

Inositol poly- and pyrophosphates (InsPs and PP-InsPs) are central eukaryotic messengers. These very highly phosphorylated molecules can exist in two distinct conformations, a canonical one with five phosphoryl groups in equatorial positions, and a “flipped” conformation with five axial substituents. Using 13C-labeled InsPs/PP-InsPs, the behavior of these molecules was investigated by 2D-NMR under solution conditions reminiscent of a cytosolic environment. Remarkably, the most highly phosphorylated messenger 1,5(PP)2-InsP4 (also termed InsP8) readily adopts both conformations at physiological conditions. Environmental factors—such as pH, metal cation composition, and temperature—strongly influence the conformational equilibrium. Thermodynamic data revealed that the transition of InsP8 from the equatorial to the axial conformation is, in fact, an exothermic process. The speciation of InsPs and PP-InsPs also affects their interaction with protein binding partners; addition of Mg2+ decreased the binding constant Kd of InsP8 to an SPX protein domain. The results illustrate that PP-InsP speciation reacts very sensitively to solution conditions, suggesting it might act as an environment-responsive molecular switch.

The suppression of TdMRP3 genes reduces the phytic acid and increases the nutrient accumulation in durum wheat grain

Micronutrient malnutrition affects more than half of the world population. Reduced bioavailability of microelements in the raw materials is considered one of the main causes of mineral deficiency in populations whose diet is largely based on the consumption of staple crops. In this context, the production of low phytic acid (lpa) cereals is a main goal of the breeding programs, as phytic acid (PA) binds essential mineral cations such as iron (Fe), zinc (Zn), manganese (Mn), potassium (K), calcium (Ca) and magnesium (Mg) precipitating in the form of phytate salts poorly digested by monogastric animals, including humans, due to the lack of phytases in the digestive tract. Since PA limits the bioavailability of microelements, it is widely recognized as an anti-nutritional compound. A Targeting Induced Local Lesions IN Genomes (TILLING) approach has been undertaken to silence the genes encoding the TdABCC13 proteins, known as Multidrug-Resistance associated Proteins 3 (TdMRP3), transporters involved in the accumulation of PA inside the vacuole in durum wheat. The TdMRP3 complete null genotypes showed a significant reduction in the content of PA and were able to accumulate a higher amount of essential micronutrients (Fe, Zn, Mn) compared to the control. The number of spikelets and seeds per spike, traits associated with the agronomic performances, were reduced compared to the control, but the negative effect was in part balanced by the increased grain weight. The TdMRP3 mutant lines showed morphological differences in the root apparatus such as a significant decrease in the number of root tips, root length, volume and surface area and an increase in root average diameter compared to the control plants. These materials represent a promising basis for obtaining new commercial durum wheats with higher nutritional value.

Immunotherapeutic Value of MAP1LC3C and Its Candidate FDA-Approved Drugs Identified by Pan-Cancer Analysis, Virtual Screening and Sensitivity Analysis

Background: The autophagy pathway within the tumour microenvironment can be regulated to inhibit or promote tumour development. In the fight against tumour growth, immunotherapy induces an anti-tumour immune response, whereas autophagy modulates this immune response. A key protein in the autophagy pathway, microtubule-associated protein 1 light chain 3 (MAP1LC3), has recently become a hotspot for tumour research. As a relatively novel member, the function of MAP1LC3C in tumours still need to be investigated. Therefore, the goal of this study was to look into the possible link between MAP1LC3C and immunotherapy for 33 kinds of human malignancies by using pan-cancer analysis. Methods: High-throughput sequencing data from The Cancer Genome Atlas, Genotype-Tissue Expression Project and Cancer Cell Line Encyclopedia databases, combined with clinical data, were used to analyze the expression of MAP1LC3C in 33 types of cancer, as well as patient prognosis and neoplasm staging. Activity scores were calculated using ssGSEA to assess the MAP1LC3C activity in pan-cancer. Associations between MAP1LC3C and the tumour microenvironment, including immune cell infiltration and immunomodulators, were analyzed. Moreover, tumour tissue ImmuneScores and StromalScores were analyzed using the ESTIMATE algorithm. Additionally, associations between MAP1LC3C and tumour mutational burden/microsatellite instability, were investigated. Finally, based on the expression and structure of MAP1LC3C, the United States Food and Drug Administration (FDA)-approved drugs, were screened by virtual screening, molecular docking and NCI-60 drug sensitivity analysis. Results: Our study found that MAP1LC3C was differentially expressed in tumour and normal tissues in 23 of 33 human cancer types, among which MAP1LC3C had prognostic effects in 12 cancer types, and MAP1LC3C expression was significantly correlated with tumour stage in four cancer types. In addition, MAP1LC3C activity in 14 cancer types was consistent with changes in transcription levels. Moreover, MAP1LC3C strongly correlated with immune infiltration, immune modulators and immune markers. Finally, a number of FDA-approved drugs were identified via virtual screening and drug sensitivity analysis. Conclusion: Our study investigated the prognostic and immunotherapeutic value of MAP1LC3C in 33 types of cancer, and several FDA-approved drugs were identified to be highly related to MAP1LC3C and can be potential cancer therapeutic candidates.

Structural evidence for visual arrestin priming via complexation of phosphoinositols

Visual arrestin (Arr1) terminates rhodopsin signaling by blocking its interaction with transducin. To do this, Arr1 translocates from the inner to the outer segment of photoreceptors upon light stimulation. Mounting evidence indicates that inositol phosphates (InsPs) affect Arr1 activity, but the Arr1-InsP molecular interaction remains poorly defined. We report the structure of bovine Arr1 in a ligand-free state featuring a near-complete model of the previously unresolved C-tail, which plays a crucial role in regulating Arr1 activity. InsPs bind to the N-domain basic patch thus displacing the C-tail, suggesting that they prime Arr1 for interaction with rhodopsin and help direct Arr1 translocation. These structures exhibit intact polar cores, suggesting that C-tail removal by InsP binding is insufficient to activate Arr1. These results show how Arr1 activity can be controlled by endogenous InsPs in molecular detail.

Supramolecular interaction of inositol phosphates with Cu(II): comparative study InsP6-InsP3

myo-inositol phosphates are an important group of biomolecules that are present in all eukaryotic cells. The most abundant member of this family in nature is InsP6 (H12L1), which interacts strongly...

Inositol Phosphates and Retroviral Assembly: A Cellular Perspective

Understanding the molecular mechanisms of retroviral assembly has been a decades-long endeavor. With the recent discovery of inositol hexakisphosphate (IP6) acting as an assembly co-factor for human immunodeficiency virus (HIV), great strides have been made in retroviral research. In this review, the enzymatic pathways to synthesize and metabolize inositol phosphates (IPs) relevant to retroviral assembly are discussed. The functions of these enzymes and IPs are outlined in the context of the cellular biology important for retroviruses. Lastly, the recent advances in understanding the role of IPs in retroviral biology are surveyed.

Phytate as a phosphorus nutrient with impacts on iron stress-related gene expression for phytoplankton: insights from diatom Phaeodactylum tricornutum

Phytoplankton have evolved a capability to acquire phosphorus (P) from dissolved organic phosphorus (DOP) since the preferred form, dissolved inorganic phosphate (DIP, or Pi), is often limited in parts of the ocean. Phytic acid (PA) is abundantly synthesized in plants and rich in excreta of animals, potentially enriching the DOP pool in coastal oceans. However, whether and how PA may be used by phytoplankton are poorly understood. Here, we investigated PA utilization and underlying metabolic pathways in the diatom model Phaeodactylum tricornutum. The physiological results showed that P. tricornutum could utilize PA as a sole source of P nutrient to support growth. Meanwhile, the replacement of PA for DIP also caused changes in multiple cellular processes such as inositol phosphate metabolism, photosynthesis, and signal transduction. These results suggest that PA is bioavailable to P. tricornutum and can directly participate the metabolic pathways of PA-grown cells. However, our data showed that the utilization of PA was markedly less efficient than that of DIP, and PA-grown cells exhibited P and iron (Fe) nutrient stress signals. Implicated in these findings is the potential of complicated responses of phytoplankton to an ambient DOP species, which calls for more systematic investigation. IMPORTANCE PA is abundant in plants, and cannot be digested by non-ruminant animals. Hence, it is potentially a significant component of the DOP pool in the coastal waters. Despite the potential importance, there is little information about its bioavailability to phytoplankton as a source of P nutrient and if so what molecular mechanisms are involved. In this study, we found that part of PA could be utilized by the diatom P. tricornutum to support growth, and another portion of PA can act as a substrate directly participating in various metabolism pathways and cellular processes. However, our physiological and transcriptomic data show that PA-grown cells still exhibited signs of P stress and potential Fe stress. These results have significant implications in phytoplankton P nutrient ecology and provide a novel insight into multi-faceted impacts of DOP utilization on phytoplankton nutrition and metabolism.

5-IP7 is a GPCR messenger mediating neural control of synaptotagmin-dependent insulin exocytosis and glucose homeostasis

5-diphosphoinositol pentakisphosphate (5-IP₇) is a signalling metabolite linked to various cellular processes. How extracellular stimuli elicit 5-IP₇ signalling remains unclear. Here we show that 5-IP₇ in β cells mediates parasympathetic stimulation of synaptotagmin-7 (Syt7)-dependent insulin release. Mechanistically, vagal stimulation and activation of muscarinic acetylcholine receptors triggers G_αq-PLC-PKC-PKD-dependent signalling and activates IP6K1, the 5-IP₇ synthase. Whereas both 5-IP₇ and its precursor IP₆ compete with PIP₂ for binding to Syt7, Ca²⁺ selectively binds 5-IP₇ with high affinity, freeing Syt7 to enable fusion of insulin-containing vesicles with the cell membrane. β-cell-specific IP6K1 deletion diminishes insulin secretion and glucose clearance elicited by muscarinic stimulation, whereas mice carrying a phosphorylation-mimicking, hyperactive IP6K1 mutant display augmented insulin release, congenital hyperinsulinaemia and obesity. These phenotypes are absent in mice lacking Syt7. Our study proposes a new conceptual framework for inositol pyrophosphate physiology in which 5-IP₇ acts as a GPCR second messenger at the interface between peripheral nervous system and metabolic organs, transmitting G_q-coupled GPCR stimulation to unclamp Syt7-dependent, and perhaps other, exocytotic events.

Inositol polyphosphate-protein interactions: Implications for microbial pathogenicity

Inositol polyphosphates (IPs) and inositol pyrophosphates (PP-IPs) regulate diverse cellular processes in eukaryotic cells. IPs and PP-IPs are highly negatively charged and exert their biological effects by interacting with specific protein targets. Studies performed predominantly in mammalian cells and model yeasts have shown that IPs and PP-IPs modulate target function through allosteric regulation, by promoting intra- and intermolecular stabilization and, in the case of PP-IPs, by donating a phosphate from their pyrophosphate (PP) group to the target protein. Technological advances in genetics have extended studies of IP function to microbial pathogens and demonstrated that disrupting PP-IP biosynthesis and PP-IP-protein interaction has a profound impact on pathogenicity. This review summarises the complexity of IP-mediated regulation in eukaryotes, including microbial pathogens. It also highlights examples of poor conservation of IP-protein interaction outcome despite the presence of conserved IP-binding domains in eukaryotic proteomes.

Dissecting the structural features of β-arrestins as multifunctional proteins

β-arrestins bind active G protein-coupled receptors (GPCRs) and play a crucial role in receptor desensitization and internalization. The classical paradigm of arrestin function has been expanded with the identification of many non-receptor-binding partners, which indicated the multifunctional role of β-arrestins in cellular functions. To elucidate the molecular mechanism of β-arrestin-mediated signaling, the structural features of β-arrestins were investigated using X-ray crystallography and cryogenic electron microscopy (cryo-EM). However, the intrinsic conformational flexibility of β-arrestins hampers the elucidation of structural interactions between β-arrestins and their binding partners using conventional structure determination tools. Therefore, structural information obtained using complementary structure analysis techniques would be necessary in combination with X-ray crystallography and cryo-EM data. In this review, we describe how β-arrestins interact with their binding partners from a structural point of view, as elucidated by both traditional methods (X-ray crystallography and cryo-EM) and complementary structure analysis techniques.

Trial design and baseline characteristics of CaLIPSO: a randomized, double-blind placebo-controlled trial of SNF472 in patients receiving haemodialysis with cardiovascular calcification

BACKGROUND

The objective of CaLIPSO, a Phase 2b, randomized, double-blind, placebo-controlled clinical trial, is to test the hypothesis that myo-inositol hexaphosphate (SNF472) attenuates the progression of cardiovascular calcification in patients receiving maintenance haemodialysis. Here we report the trial design and baseline characteristics of trial participants.

METHODS

Adult patients on maintenance haemodialysis (≥6 months) with an Agatston coronary artery calcium score, as measured by a multidetector computed tomography scanner, of 100-3500 U were enrolled. Patients were stratified by Agatston score (100-<400, 400-1000 or >1000 U) and randomized in a 1:1:1 ratio to receive placebo, SNF472 300 mg or SNF472 600 mg administered intravenously three times weekly during each haemodialysis session.

RESULTS

Overall, 274 patients were randomized. The mean age of trial participants was 63.6 (standard deviation 8.9) years and 39% were women. The coronary artery, aorta and aortic valve median (25th-75th percentile) Agatston scores at baseline were 730 U (315-1435), 1728 U (625-4978) and 103 U (31-262), respectively, and the median (25th-75th percentile) calcium volume scores at baseline were 666 (310-1234), 1418 (536-4052) and 107 (38-278), respectively. Older age and diabetes mellitus were associated with higher calcium scores at baseline.

CONCLUSIONS

The CaLIPSO trial enrolled patients on haemodialysis with pre-existent cardiovascular calcification to test the hypothesis that SNF472 attenuates its progression in the coronary arteries, aorta and aortic valve.

Overview of Inositol and Inositol Phosphates on Chemoprevention of Colitis-Induced Carcinogenesis

Chronic inflammation is one of the most common and well-recognized risk factors for human cancer, including colon cancer. Inflammatory bowel disease (IBD) is defined as a longstanding idiopathic chronic active inflammatory process in the colon, including ulcerative colitis and Crohn's disease. Importantly, patients with IBD have a significantly increased risk for the development of colorectal carcinoma. Dietary inositol and its phosphates, as well as phospholipid derivatives, are well known to benefit human health in diverse pathologies including cancer prevention. Inositol phosphates including InsP3, InsP6, and other pyrophosphates, play important roles in cellular metabolic and signal transduction pathways involved in the control of cell proliferation, differentiation, RNA export, DNA repair, energy transduction, ATP regeneration, and numerous others. In the review, we highlight the biologic function and health effects of inositol and its phosphates including the nature and sources of these molecules, potential nutritional deficiencies, their biologic metabolism and function, and finally, their role in the prevention of colitis-induced carcinogenesis.

MINPP1 prevents intracellular accumulation of the chelator inositol hexakisphosphate and is mutated in Pontocerebellar Hypoplasia

Inositol polyphosphates are vital metabolic and secondary messengers, involved in diverse cellular functions. Therefore, tight regulation of inositol polyphosphate metabolism is essential for proper cell physiology. Here, we describe an early-onset neurodegenerative syndrome caused by loss-of-function mutations in the multiple inositol-polyphosphate phosphatase 1 gene (MINPP1). Patients are found to have a distinct type of Pontocerebellar Hypoplasia with typical basal ganglia involvement on neuroimaging. We find that patient-derived and genome edited MINPP1^−/− induced stem cells exhibit an inefficient neuronal differentiation combined with an increased cell death. MINPP1 deficiency results in an intracellular imbalance of the inositol polyphosphate metabolism. This metabolic defect is characterized by an accumulation of highly phosphorylated inositols, mostly inositol hexakisphosphate (IP₆), detected in HEK293 cells, fibroblasts, iPSCs and differentiating neurons lacking MINPP1. In mutant cells, higher IP₆ level is expected to be associated with an increased chelation of intracellular cations, such as iron or calcium, resulting in decreased levels of available ions. These data suggest the involvement of IP₆-mediated chelation on Pontocerebellar Hypoplasia disease pathology and thereby highlight the critical role of MINPP1 in the regulation of human brain development and homeostasis.

Tight regulation of inositol polyphosphate metabolism is essential for proper cell physiology. Here, the authors describe an early-onset neurodegenerative syndrome caused by loss-of-function mutations in the MINPP1 gene, characterised by intracellular imbalance of inositol polyphosphate metabolism.

Analysis of inositol phosphate metabolism by capillary electrophoresis electrospray ionization mass spectrometry

The analysis of myo-inositol phosphates (InsPs) and myo-inositol pyrophosphates (PP-InsPs) is a daunting challenge due to the large number of possible isomers, the absence of a chromophore, the high charge density, the low abundance, and the instability of the esters and anhydrides. Given their importance in biology, an analytical approach to follow and understand this complex signaling hub is desirable. Here, capillary electrophoresis (CE) coupled to electrospray ionization mass spectrometry (ESI-MS) is implemented to analyze complex mixtures of InsPs and PP-InsPs with high sensitivity. Stable isotope labeled (SIL) internal standards allow for matrix-independent quantitative assignment. The method is validated in wild-type and knockout mammalian cell lines and in model organisms. SIL-CE-ESI-MS enables the accurate monitoring of InsPs and PP-InsPs arising from compartmentalized cellular synthesis pathways, by feeding cells with either [¹³C₆]-myo-inositol or [¹³C₆]-D-glucose. In doing so, we provide evidence for the existence of unknown inositol synthesis pathways in mammals, highlighting the potential of this method to dissect inositol phosphate metabolism and signalling.

Myo-Inositol phosphates (InsPs) and pyrophosphates (PP-InsPs) are important second messengers but their analysis remains challenging. Here, the authors develop a capillary electrophoresis-mass spectrometry method for the identification and quantitation of InsP and PP-InsP isomers in cells and tissues.

The Key Role of IP6K: A Novel Target for Anticancer Treatments?

Inositol and its phosphate metabolites play a pivotal role in several biochemical pathways and gene expression regulation: inositol pyrophosphates (PP-IPs) have been increasingly appreciated as key signaling modulators. Fluctuations in their intracellular levels hugely impact the transfer of phosphates and the phosphorylation status of several target proteins. Pharmacological modulation of the proteins associated with PP-IP activities has proved to be beneficial in various pathological settings. IP₇ has been extensively studied and found to play a key role in pathways associated with PP-IP activities. Three inositol hexakisphosphate kinase (IP₆K) isoforms regulate IP₇ synthesis in mammals. Genomic deletion or enzymic inhibition of IP₆K1 has been shown to reduce cell invasiveness and migration capacity, protecting against chemical-induced carcinogenesis. IP₆K1 could therefore be a useful target in anticancer treatment. Here, we summarize the current understanding that established IP₆K1 and the other IP₆K isoforms as possible targets for cancer therapy. However, it will be necessary to determine whether pharmacological inhibition of IP₆K is safe enough to begin clinical study. The development of safe and selective inhibitors of IP₆K isoforms is required to minimize undesirable effects.

Suramin and NF449 are IP5K inhibitors that disrupt inositol hexakisphosphate-mediated regulation of cullin-RING ligase and sensitize cancer cells to MLN4924/pevonedistat

Inositol hexakisphosphate (IP₆) is an abundant metabolite synthesized from inositol 1,3,4,5,6-pentakisphosphate (IP₅) by the single IP₅ 2-kinase (IP5K). Genetic and biochemical studies have shown that IP₆ usually functions as a structural cofactor in protein(s) mediating mRNA export, DNA repair, necroptosis, 3D genome organization, HIV infection, and cullin-RING ligase (CRL) deneddylation. However, it remains unknown whether pharmacological perturbation of cellular IP₆ levels affects any of these processes. Here, we performed screening for small molecules that regulate human IP5K activity, revealing that the antiparasitic drug and polysulfonic compound suramin efficiently inhibits IP5K in vitro and in vivo The results from docking experiments and biochemical validations suggested that the suramin targets IP5K in a distinct bidentate manner by concurrently binding to the ATP- and IP₅-binding pockets, thereby inhibiting both IP₅ phosphorylation and ATP hydrolysis. NF449, a suramin analog with additional sulfonate moieties, more potently inhibited IP5K. Both suramin and NF449 disrupted IP₆-dependent sequestration of CRL by the deneddylase COP9 signalosome, thereby affecting CRL activity cycle and component dynamics in an IP5K-dependent manner. Finally, nontoxic doses of suramin, NF449, or NF110 exacerbate the loss of cell viability elicited by the neddylation inhibitor and clinical trial drug MLN4924/pevonedistat, suggesting synergistic ef-fects. Suramin and its analogs provide structural templates for designing potent and specific IP5K inhibitors, which could be used in combination therapy along with MLN4924/pevonedistat. IP5K is a potential mechanistic target of suramin, accounting for suramin's therapeutic effects.

Targeting the Inositol Pyrophosphate Biosynthetic Enzymes in Metabolic Diseases

In mammals, a family of three inositol hexakisphosphate kinases (IP6Ks) synthesizes the inositol pyrophosphate 5-IP7 from IP6. Genetic deletion of Ip6k1 protects mice from high fat diet induced obesity, insulin resistance and fatty liver. IP6K1 generated 5-IP7 promotes insulin secretion from pancreatic β-cells, whereas it reduces insulin signaling in metabolic tissues by inhibiting the protein kinase Akt. Thus, IP6K1 promotes high fat diet induced hyperinsulinemia and insulin resistance in mice while its deletion has the opposite effects. IP6K1 also promotes fat accumulation in the adipose tissue by inhibiting the protein kinase AMPK mediated energy expenditure. Genetic deletion of Ip6k3 protects mice from age induced fat accumulation and insulin resistance. Accordingly, the pan IP6K inhibitor TNP [N2-(m-trifluorobenzyl), N6-(p-nitrobenzyl)purine] ameliorates obesity, insulin resistance and fatty liver in diet induced obese mice by improving Akt and AMPK mediated insulin sensitivity and energy expenditure. TNP also protects mice from bone loss, myocardial infarction and ischemia reperfusion injury. Thus, the IP6K pathway is a potential target in obesity and other metabolic diseases. Here, we summarize the studies that established IP6Ks as a potential target in metabolic diseases. Further studies will reveal whether inhibition of this pathway has similar pleiotropic benefits on metabolic health of humans.

Solution Studies and Crystal Structures of Heteropolynuclear Potassium/Copper Complexes with Phytate and Aromatic Polyamines: Self-Assembly through Coordinative and Supramolecular Interactions

Phytate (L^12- ) is a relevant natural product. It interacts strongly with biologically relevant cations, due to the high negative charge exhibited in a wide pH range. The synthesis and crystal structures of the mixed-ligand Cu(II) polynuclear complexes K(H₂ tptz)_0.5 [Cu(H₈ L)(tptz)] ⋅ 3.6H₂ O (1), K(H₂ O)₃ {[Cu(H₂ O)(bpca)]₃ (H₈ L)} ⋅ 1.75H₂ O (2), and K_1.5 (H₂ O)₂ [Cu(bpca)](H_9.5 L) ⋅ 8H₂ O (3) (tptz=2,4,6-tri(pyridin-2-yl)-1,3,5-triazine; Hbpca=bis(2-pyridylcarbonyl) amine) are reported herein. They were obtained by the use of an aromatic rigid amine, which satisfies some of the metal coordination sites and promotes the hierarchical assembly of 2D polymeric structures. Speciation of phytate-Cu(II)-Hbpca system and determination of complex stability constants were performed by means of potentiometric titrations, in 0.15 M NMe₄ Cl at 37.0 °C, showing that, even in solution, this system is able to produce highly aggregated complexes, such as [Cu₃ (bpca)₃ (H₇ L)]^2- . Furthermore, the Cu(II)-mediated tptz hydrolysis was studied by UV-vis spectroscopy at room temperature in 0.15 M NMe₄ Cl. Based on the equilibrium results and with the aid of molecular modelling tools, a plausible self-assembly process for 2 and 3 could be proposed.

A Short Historical Perspective of Methods in Inositol Phosphate Research

The multitudinous inositol phosphate family elicits a wide range of molecular effects that regulate countless biological responses. In this review, I provide a methodological viewpoint of the manner in which key advances in the field of inositol phosphate research were made. I also note some of the considerable challenges that still lie ahead.

SNF472, a novel anti-crystallization agent, inhibits induced calcification in an in vitro model of human aortic valve calcification

The purpose of the present study was to investigate whether SNF472, the hexasodium salt of myo-inositol hexaphosphate (IP6 or phytate): 1. Inhibits induced calcification in cultured aortic valve interstitial cells (VIC) as an in vitro model of aortic valve stenosis and 2. Whether inhibition is different in VIC obtained from healthy and calcified aortic valves. VIC from healthy (n = 5) and calcified (n = 7) human aortic valves were seeded in basic growth medium, osteogenic differentiation medium alone, or in osteogenic medium with SNF472 (3, 10, and 30 μM) and cultivated for 3 weeks. Calcification was quantified spectrophotometrically after Alizarin Red staining. In VIC from calcified valves, a complete inhibition of calcification was observed with SNF472 concentrations of 10 and 30 μM (p < .01), significantly stronger than in VIC from healthy valves. When SNF472 was added to VIC after 1 week in osteogenic medium, 30 and 100 μM SNF472 inhibited the progression of ongoing calcification by 81 and 100% (p < .01), respectively. The same concentrations of SNF472 given after 2 weeks reduced calcification by 35 and 40% respectively (not significant). SNF472 inhibited both the formation and the progression of calcification with the strongest effect in VIC from calcified valves.

Extracellular vesicles from Echinococcus granulosus larval stage: Isolation, characterization and uptake by dendritic cells

The secretion of extracellular vesicles (EVs) in helminth parasites is a constitutive mechanism that promotes survival by improving their colonization and adaptation in the host tissue. In the present study, we analyzed the production of EVs from supernatants of cultures of Echinococcus granulosus protoscoleces and metacestodes and their interaction with dendritic cells, which have the ability to efficiently uptake and process microbial antigens, activating T lymphocytes. To experimentally increase the release of EVs, we used loperamide, a calcium channel blocker that increases the cytosolic calcium level in protoscoleces and EV secretion. An exosome-like enriched EV fraction isolated from the parasite culture medium was characterized by dynamic light scattering, transmission electron microscopy, proteomic analysis and immunoblot. This allowed identifying many proteins including: small EV markers such as TSG101, SDCBP, ALIX, tetraspanins and 14-3-3 proteins; proteins involved in vesicle-related transport; orthologs of mammalian proteins involved in the immune response, such as basigin, Bp29 and maspardin; and parasite antigens such as antigen 5, P29 and endophilin-1, which are of special interest due to their role in the parasite-host relationship. Finally, studies on the EVs-host cell interaction demonstrated that E. granulosus exosome-like vesicles were internalized by murine dendritic cells, inducing their maturation with increase of CD86 and with a slight down-regulation in the expression of MHCII molecules. These data suggest that E. granulosus EVs could interfere with the antigen presentation pathway of murine dendritic cells inducing immunoregulation in the host. Further studies are needed to better understand the role of these vesicles in parasite survival and as diagnostic markers and new vaccines.

Human cystic echinococcosis, caused by chronic infection with the larval stage of Echinococcus granulosus, affects over 1 million people worldwide. This helminth parasite secretes numerous excretory/secretory products that are in contact with host tissues where it establishes hydatid cysts. In this study, we comprehensively characterized extracellular vesicles (EVs) from E. granulosus protoscoleces and metacestodes, and demonstrated for the first time that the exosome-like vesicles from helminths can interact with host dendritic cells and carry several immunoregulatory proteins. This study provides valuable data on cestode-host immune communication. Nevertheless, further research on EVs is needed to fully understand their role in the parasite-host interface and obtain new data concerning their function as therapeutic markers and diagnostic tools.

Structural Analysis of the Bacterial Effector AvrA Identifies a Critical Helix Involved in Substrate Recognition

Bacterial effector proteins are essential for the infection and proliferation of pathogenic bacteria through manipulation of host immune response pathways. AvrA is a Salmonella effector that belongs to the YopJ family of acetyltransferases, which suppresses c-JUN N-terminal kinase (JNK) signaling in mammals through acetylation of mitogen-activated receptor kinase kinases 4 and 7 (MKK4/7). Interestingly, there are two paralogues of AvrA that differ by only a single internal leucine residue, which when absent (AvrA^ΔL140) abrogates the ability to suppress JNK signaling. Here, we present the first crystal structure of a bacterial effector from an animal pathogen, AvrA^ΔL140, accompanied by a thorough biophysical characterization of both AvrA variants. The structure in complex with inositol hexaphosphate and coenzyme A reveals two closely associated domains consisting of a catalytic core that resembles the CE clan peptidases and a wedge-shaped regulatory region that mediates cofactor and substrate binding. The loss of the putative function of AvrA^ΔL140 is due to its inability to interact with MKK4/7, which ultimately arises from an altered conformation of a critical helix adjacent to the active site that harbors L140. These results provide general insights into substrate recognition across the YopJ family of acetyltransferases.

Inositol polyphosphates regulate and predict yeast pseudohyphal growth phenotypes

Pseudohyphal growth is a nutrient-regulated program in which budding yeast form multicellular filaments of elongated and connected cells. Filamentous growth is required for virulence in pathogenic fungi and provides an informative model of stress-responsive signaling. The genetics and regulatory networks modulating pseudohyphal growth have been studied extensively, but little is known regarding the changes in metabolites that enable pseudohyphal filament formation. Inositol signaling molecules are an important class of metabolite messengers encompassing highly phosphorylated and diffusible inositol polyphosphates (InsPs). We report here that the InsP biosynthesis pathway is required for wild-type pseudohyphal growth. Under nitrogen-limiting conditions that can induce filamentation, InsPs exhibit characteristic profiles, distinguishing the InsP₇ pyrophosphate isoforms 1PP-InsP₅ and 5PP-InsP₅. Deletion and overexpression analyses of InsP kinases identify elevated levels of 5PP-InsP₅ relative to 1PP-InsP₅ in mutants exhibiting hyper-filamentous growth. Overexpression of KCS1, which promotes formation of inositol pyrophosphates, is sufficient to drive pseudohyphal filamentation on medium with normal nitrogen levels. We find that the kinases Snf1p (AMPK), Kss1p, and Fus3p (MAPKs), required for wild-type pseudohyphal growth, are also required for wild-type InsP levels. Deletion analyses of the corresponding kinase genes indicate elevated InsP₃ levels and an absence of exaggerated 5PP-InsP₅ peaks in trace profiles from snf1Δ/Δ and kss1Δ/Δ mutants exhibiting decreased pseudohyphal filamentation. Elevated 5PP-InsP₅:1PP-InsP₅ ratios are present in the hyperfilamentous fus3 deletion mutant. Collectively, the data identify the presence of elevated 5PP-InsP₅ levels relative to other inositol pyrophosphates as an in vivo marker of hyper-filamentous growth, while providing initial evidence for the regulation of InsP signaling by pseudohyphal growth kinases.

Changes in metabolite levels underlie important biological processes, including cellular responses to nutrient stress. One such response encompasses the nitrogen stress-induced transition of budding yeast cells into multicellular filaments, relevant as a model of directional growth and fungal pathogenesis. We report here that a conserved family of charged lipid-derived metabolites, inositol polyphosphates, exhibits characteristic changes as yeast cell form filaments in response to conditions of nitrogen limitation. The ratios of doubly charged inositol pyrophosphates consistently match with the degree of filament formation. Enzymes of the inositol polyphosphate synthesis pathway are required for filament formation, and inositol polyphosphate levels are dependent on kinases that enable wild-type filamentation. Our data indicate that inositol polyphosphates mark filamentous growth states, highlighting a new regulatory role for these ubiquitous eukaryotic second messengers.

Structural and functional analysis of mRNA export regulation by the nuclear pore complex

The nuclear pore complex (NPC) controls the passage of macromolecules between the nucleus and cytoplasm, but how the NPC directly participates in macromolecular transport remains poorly understood. In the final step of mRNA export, the DEAD-box helicase DDX19 is activated by the nucleoporins Gle1, Nup214, and Nup42 to remove Nxf1•Nxt1 from mRNAs. Here, we report crystal structures of Gle1•Nup42 from three organisms that reveal an evolutionarily conserved binding mode. Biochemical reconstitution of the DDX19 ATPase cycle establishes that human DDX19 activation does not require IP₆, unlike its fungal homologs, and that Gle1 stability affects DDX19 activation. Mutations linked to motor neuron diseases cause decreased Gle1 thermostability, implicating nucleoporin misfolding as a disease determinant. Crystal structures of human Gle1•Nup42•DDX19 reveal the structural rearrangements in DDX19 from an auto-inhibited to an RNA-binding competent state. Together, our results provide the foundation for further mechanistic analyses of mRNA export in humans.

The export of mRNA to the cytosol depends on the nuclear pore complex (NPC) and the activation of the helicase DDX19, but their interplay in humans remains poorly understood. Here, the authors present a structural and functional analysis of DDX19 activation, revealing how the human NPC regulates mRNA export.

Characterization of SNF472 pharmacokinetics and efficacy in uremic and non-uremic rats models of cardiovascular calcification

End-stage renal disease is strongly associated with progressive cardiovascular calcification (CVC) and there is currently no therapy targeted to treat CVC. SNF472 is an experimental formulation under development for treatment of soft tissue calcification. We have investigated the pharmacokinetics of SNF472 administration in rats and its inhibitory effects on CVC. SNF472 was studied in three rat models: (1) prevention of vitamin D₃-induced CVC with an intravenous SNF472 bolus of 1 mg/kg SNF472, (2) inhibition of progression of vitamin D₃-induced CVC with a subcutaneous SNF472 bolus of 10 or 60 mg/kg SNF472, starting after calcification induction, (3) CVC in adenine-induced uremic rats treated with 50 mg/kg SNF472 via i.v. 4h -infusion. Uremic rats presented lower plasma levels of SNF472 than control animals after i.v. infusion. CVC in non-uremic rats was inhibited by 60–70% after treatment with SNF472 and progression of cardiac calcification completely blocked. Development of CVC in uremic rats was inhibited by up to 80% following i.v. infusion of SNF472. SNF472 inhibits the development and progression of CVC in uremic and non-uremic rats in the same range of SNF472 plasma levels but using in each case the required dose to obtain those levels. These results collectively support the development of SNF472 as a novel therapeutic option for treatment of CVC in humans.

SNF472, a novel inhibitor of vascular calcification, could be administered during hemodialysis to attain potentially therapeutic phytate levels

BACKGROUND

Cardiovascular calcification (CVC) is a major concern in hemodialysis (HD) and the loss of endogenous modulators of calcification seems involved in the process. Phytate is an endogenous crystallization inhibitor and its low molecular mass and high water solubility make it potentially dialyzable. SNF472 (the hexasodium salt of phytate) is being developed for the treatment of calciphylaxis and CVC in HD patients. We aimed to verify if phytate is lost during dialysis, and evaluate SNF472's behaviour during dialysis.

METHODS

Dialyzability was assessed in vitro using online-hemodiafiltration and high-flux HD systems in blood and saline. SNF472 was infused for 20 min and quantified at different time points.

RESULTS

Phytate completely dialyzed in 1 h at low concentrations (10 mg/l) but not when added at 30 or 66.67 mg/l SNF472. In bypass conditions, calcium was slightly chelated during SNF472 infusion but when the system was switched to dialysis mode the calcium in the bath compensated this chelation.

CONCLUSION

Phytate dialyses with a low clearance. The administration of SNF472 as an exogenous source of phytate allows to attain supra-physiological levels required for its potential therapeutic properties. As SNF472 is infused during the whole dialysis session, the low clearance would not affect the drug's systemic exposure.

Phytase overexpression in Arabidopsis improves plant growth under osmotic stress and in combination with phosphate deficiency

Engineering osmotolerant plants is a challenge for modern agriculture. An interaction between osmotic stress response and phosphate homeostasis has been reported in plants, but the identity of molecules involved in this interaction remains unknown. In this study we assessed the role of phytic acid (PA) in response to osmotic stress and/or phosphate deficiency in Arabidopsis thaliana. For this purpose, we used Arabidopsis lines (L7 and L9) expressing a bacterial beta-propeller phytase PHY-US417, and a mutant in inositol polyphosphate kinase 1 gene (ipk1-1), which were characterized by low PA content, 40% (L7 and L9) and 83% (ipk1-1) of the wild-type (WT) plants level. We show that the PHY-overexpressor lines have higher osmotolerance and lower sensitivity to abscisic acid than ipk1-1 and WT. Furthermore, PHY-overexpressors showed an increase by more than 50% in foliar ascorbic acid levels and antioxidant enzyme activities compared to ipk1-1 and WT plants. Finally, PHY-overexpressors are more tolerant to combined mannitol stresses and phosphate deficiency than WT plants. Overall, our results demonstrate that the modulation of PA improves plant growth under osmotic stress, likely via stimulation of enzymatic and non-enzymatic antioxidant systems, and that beside its regulatory role in phosphate homeostasis, PA may be also involved in fine tuning osmotic stress response in plants.

Yb(OTf)3-Catalyzed Desymmetrization of myo-Inositol 1,3,5-Orthoformate and Its Application in the Synthesis of Chiral Inositol Phosphates

A variety of inositol phosphates including myo-inositol 1,4,5-trisphosphate, which is a secondary messenger in transmembrane signaling, were selectively synthesized via Yb(OTf)₃-catalyzed desymmetrization of myo-inositol 1,3,5-orthoformate using a proline-based chiral anhydride as an acylation precursor. The investigated catalytic system could regioselectively differentiate the enantiotopic hydroxy groups of myo-inositol 1,3,5-orthoformate in the presence of a chiral auxiliary. This key step to generate a suitably protected chiral myo-inositol derivatives is described here as a unified approach to access inositol phosphates.

Has Inositol Played Any Role in the Origin of Life?

Phosphorus, as phosphate, plays a paramount role in biology. Since phosphate transfer reactions are an integral part of contemporary life, phosphate may have been incorporated into the initial molecules at the very beginning. To facilitate the studies into early phosphate utilization, we should look retrospectively to phosphate-rich molecules present in today’s cells. Overlooked by origin of life studies until now, inositol and the inositol phosphates, of which some species possess more phosphate groups that carbon atoms, represent ideal molecules to consider in this context. The current sophisticated association of inositol with phosphate, and the roles that some inositol phosphates play in regulating cellular phosphate homeostasis, intriguingly suggest that inositol might have played some role in the prebiotic process of phosphate exploitation. Inositol can be synthesized abiotically and, unlike glucose or ribose, is chemically stable. This stability makes inositol the ideal candidate for the earliest organophosphate molecules, as primitive inositol phosphates. I also present arguments suggesting roles for some inositol phosphates in early chemical evolution events. Finally, the possible prebiotic synthesis of inositol pyrophosphates could have generated high-energy molecules to be utilized in primitive trans-phosphorylating processes.

The crystal structure of mammalian inositol 1,3,4,5,6-pentakisphosphate 2-kinase reveals a new zinc-binding site and key features for protein function

Inositol 1,3,4,5,6-pentakisphosphate 2-kinases (IP₅ 2-Ks) are part of a family of enzymes in charge of synthesizing inositol hexakisphosphate (IP₆) in eukaryotic cells. This protein and its product IP₆ present many roles in cells, participating in mRNA export, embryonic development, and apoptosis. We reported previously that the full-length IP₅ 2-K from Arabidopsis thaliana is a zinc metallo-enzyme, including two separated lobes (the N- and C-lobes). We have also shown conformational changes in IP₅ 2-K and have identified the residues involved in substrate recognition and catalysis. However, the specific features of mammalian IP₅ 2-Ks remain unknown. To this end, we report here the first structure for a murine IP₅ 2-K in complex with ATP/IP₅ or IP₆. Our structural findings indicated that the general folding in N- and C-lobes is conserved with A. thaliana IP₅ 2-K. A helical scaffold in the C-lobe constitutes the inositol phosphate-binding site, which, along with the participation of the N-lobe, endows high specificity to this protein. However, we also noted large structural differences between the orthologues from these two eukaryotic kingdoms. These differences include a novel zinc-binding site and regions unique to the mammalian IP₅ 2-K, as an unexpected basic patch on the protein surface. In conclusion, our findings have uncovered distinct features of a mammalian IP₅ 2-K and set the stage for investigations into protein-protein or protein-RNA interactions important for IP₅ 2-K function and activity.

Synthesis of an inositol hexakisphosphate (IP6) affinity probe to study the interactome from a colon cancer cell line

Inositol hexakisphosphate (InsP6 or IP6) is an important signalling molecule in vesicular trafficking, neurotransmission, immune responses, regulation of protein kinases and phosphatases, activation of ion channels, antioxidant functions and anticancer activities. An IP6 probe was synthesised from myo-inositol via a derivatised analogue, which was immobilised through a terminal amino group onto Dynabeads. Systematic analysis of the IP6 interactome has been performed using the IP6 affinity probe using cytosolic extracts from the LIM1215 colonic carcinoma cell line. LC/MS/MS analysis identified 77 proteins or protein complexes that bind to IP6 specifically, including AP-2 complex proteins and β-arrestins as well as a number of novel potential IP6 interacting proteins. Bioinformatic enrichment analysis of the IP6 interactome reinforced the concept that IP6 regulates a number of biological processes including cell cycle and division, signal transduction, intracellular protein transport, vesicle-mediated transport and RNA splicing.

The emerging roles of inositol pyrophosphates in eukaryotic cell physiology

Inositol pyrophosphates are water soluble derivatives of inositol that contain pyrophosphate or diphosphate moieties in addition to monophosphates. The best characterised inositol pyrophosphates, are IP7 (diphosphoinositol pentakisphosphate or PP-IP5), and IP8 (bisdiphosphoinositol tetrakisphosphate or (PP)2-IP4). These energy-rich small molecules are present in all eukaryotic cells, from yeast to mammals, and are involved in a wide range of cellular functions including apoptosis, vesicle trafficking, DNA repair, osmoregulation, phosphate homeostasis, insulin sensitivity, immune signalling, cell cycle regulation, and ribosome synthesis. Identified more than 20 years ago, there is still only a rudimentary understanding of the mechanisms by which inositol pyrophosphates participate in these myriad pathways governing cell physiology and homeostasis. The unique stereochemical and bioenergetic properties these molecules possess as a consequence of the presence of one or two pyrophosphate moieties in the vicinity of densely packed monophosphates are likely to form the molecular basis for their participation in multiple signalling and metabolic pathways. The aim of this review is to provide first time researchers in this area with an introduction to inositol pyrophosphates and a comprehensive overview on their cellular functions.

Evaluation of in vitro and in vivo biocompatibility of a myo-inositol hexakisphosphate gelated polyaniline hydrogel in a rat model

Recent advances in understanding the interaction between electricity and cells/biomolecules have generated great interest in developing biocompatible electrically conductive materials. In this study, we investigated the biocompatibility of a myo-inositol hexakisphosphate gelated polyaniline hydrogel using in vitro and in vivo experiments in a rat model. The polyaniline hydrogel was used to coat a polycaprolactone scaffold and was cultured with rat endothelial progenitor cells differentiated from rat adipose-derived stem cells. Compared with the control sample on a pristine polycaprolactone scaffold, the treated polyaniline hydrogel had the same non-poisonous/cytotoxicity grade, enhanced cell adhesion, and a higher cell proliferation/growth rate. In implant studies, the polyaniline hydrogel sample induced milder inflammatory responses than did the control at the same time points. Combining the advantages of a biocompatible hydrogel and an organic conductor, the inositol phosphate-gelated polyaniline hydrogel could be used in bioelectronics applications such as biosensors, neural probes, cell stimulators, medical electrodes, tissue engineering, and electro-controlled drug delivery.

Seed Biofortification and Phytic Acid Reduction: A Conflict of Interest for the Plant?

Most of the phosphorus in seeds is accumulated in the form of phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate, InsP₆). This molecule is a strong chelator of cations important for nutrition, such as iron, zinc, magnesium, and calcium. For this reason, InsP₆ is considered an antinutritional factor. In recent years, efforts to biofortify seeds through the generation of low phytic acid (lpa) mutants have been noteworthy. Moreover, genes involved in the biosynthesis and accumulation of this molecule have been isolated and characterized in different species. Beyond its role in phosphorus storage, phytic acid is a very important signaling molecule involved in different regulatory processes during plant development and responses to different stimuli. Consequently, many lpa mutants show different negative pleitotropic effects. The strength of these pleiotropic effects depends on the specific mutated gene, possible functional redundancy, the nature of the mutation, and the spatio-temporal expression of the gene. Breeding programs or transgenic approaches aimed at development of new lpa mutants must take into consideration these different aspects in order to maximize the utility of these mutants.

Physicochemical characteristics of structurally determined metabolite-protein and drug-protein binding events with respect to binding specificity

To better understand and ultimately predict both the metabolic activities as well as the signaling functions of metabolites, a detailed understanding of the physical interactions of metabolites with proteins is highly desirable. Focusing in particular on protein binding specificity vs. promiscuity, we performed a comprehensive analysis of the physicochemical properties of compound-protein binding events as reported in the Protein Data Bank (PDB). We compared the molecular and structural characteristics obtained for metabolites to those of the well-studied interactions of drug compounds with proteins. Promiscuously binding metabolites and drugs are characterized by low molecular weight and high structural flexibility. Unlike reported for drug compounds, low rather than high hydrophobicity appears associated, albeit weakly, with promiscuous binding for the metabolite set investigated in this study. Across several physicochemical properties, drug compounds exhibit characteristic binding propensities that are distinguishable from those associated with metabolites. Prediction of target diversity and compound promiscuity using physicochemical properties was possible at modest accuracy levels only, but was consistently better for drugs than for metabolites. Compound properties capturing structural flexibility and hydrogen-bond formation descriptors proved most informative in PLS-based prediction models. With regard to diversity of enzymatic activities of the respective metabolite target enzymes, the metabolites benzylsuccinate, hypoxanthine, trimethylamine N-oxide, oleoylglycerol, and resorcinol showed very narrow process involvement, while glycine, imidazole, tryptophan, succinate, and glutathione were identified to possess broad enzymatic reaction scopes. Promiscuous metabolites were found to mainly serve as general energy currency compounds, but were identified to also be involved in signaling processes and to appear in diverse organismal systems (digestive and nervous system) suggesting specific molecular and physiological roles of promiscuous metabolites.

Relationship between Urinary Level of Phytate and Valvular Calcification in an Elderly Population: A Cross-Sectional Study

Pathological calcification generally consists of the formation of solid deposits of hydroxyapatite (calcium phosphate) in soft tissues. Supersaturation is the thermodynamic driving force for crystallization, so it is believed that higher blood levels of calcium and phosphate increase the risk of cardiovascular calcification. However several factors can promote or inhibit the natural process of pathological calcification. This cross-sectional study evaluated the relationship between physiological levels of urinary phytate and heart valve calcification in a population of elderly out subjects. A population of 188 elderly subjects (mean age: 68 years) was studied. Valve calcification was measured by echocardiography. Phytate determination was performed from a urine sample and data on blood chemistry, end-systolic volume, concomitant diseases, cardiovascular risk factors, medication usage and food were obtained. The study population was classified in three tertiles according to level of urinary phytate: low (<0.610 μM), intermediate (0.61-1.21 μM), and high (>1.21 μM). Subjects with higher levels of urinary phytate had less mitral annulus calcification and were less likely to have diabetes and hypercholesterolemia. In the multivariate analysis, age, serum phosphorous, leukocytes total count and urinary phytate excretion appeared as independent factors predictive of presence of mitral annulus calcification. There was an inverse correlation between urinary phytate content and mitral annulus calcification in our population of elderly out subjects. These results suggest that consumption of phytate-rich foods may help to prevent cardiovascular calcification evolution.

A novel method for the purification of inositol phosphates from biological samples reveals that no phytate is present in human plasma or urine

Inositol phosphates are a large and diverse family of signalling molecules. While genetic studies have discovered important functions for them, the biochemistry behind these roles is often not fully characterized. A key obstacle in inositol phosphate research in mammalian cells has been the lack of straightforward techniques for their purification and analysis. Here we describe the ability of titanium dioxide (TiO₂) beads to bind inositol phosphates. This discovery allowed the development of a new purification protocol that, coupled with gel analysis, permitted easy identification and quantification of InsP₆ (phytate), its pyrophosphate derivatives InsP₇ and InsP₈, and the nucleotides ATP and GTP from cell or tissue extracts. Using this approach, InsP₆, InsP₇ and InsP₈ were visualized in Dictyostelium extracts and a variety of mammalian cell lines and tissues, and the effects of metabolic perturbation on these were explored. TiO₂ bead purification also enabled us to quantify InsP₆ in human plasma and urine, which led to two distinct but related observations. Firstly, there is an active InsP₆ phosphatase in human plasma, and secondly, InsP₆ is undetectable in either fluid. These observations seriously question reports that InsP₆ is present in human biofluids and the advisability of using InsP₆ as a dietary supplement.

New paradigms for the chiral synthesis of inositol phosphates

Paradigms found: Inositol phosphates are biomolecules found ubiquitously in eukaryotes, in which they play a number of vital biological roles. Their enantioselective synthesis has recently received a boost from two complementary phosphorylation methods that could change the way they are synthesised, and hopefully provide invaluable chemical biology tools to further our understanding of this large family.

Autoinhibition of Bruton's tyrosine kinase (Btk) and activation by soluble inositol hexakisphosphate

Bruton's tyrosine kinase (Btk), a Tec-family tyrosine kinase, is essential for B-cell function. We present crystallographic and biochemical analyses of Btk, which together reveal molecular details of its autoinhibition and activation. Autoinhibited Btk adopts a compact conformation like that of inactive c-Src and c-Abl. A lipid-binding PH-TH module, unique to Tec kinases, acts in conjunction with the SH2 and SH3 domains to stabilize the inactive conformation. In addition to the expected activation of Btk by membranes containing phosphatidylinositol triphosphate (PIP3), we found that inositol hexakisphosphate (IP6), a soluble signaling molecule found in both animal and plant cells, also activates Btk. This activation is a consequence of a transient PH-TH dimerization induced by IP6, which promotes transphosphorylation of the kinase domains. Sequence comparisons with other Tec-family kinases suggest that activation by IP6 is unique to Btk.