GO:0000832 inositol hexakisphosphate 5-kinase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0000832 defines the enzymatic activity that converts 1D-myo-inositol hexakisphosphate (IP6) to 5-diphospho-1D-myo-inositol 1,2,3,4,6-pentakisphosphate (5-PP-IP5) using ATP.
• This activity is catalyzed by members of the inositol polyphosphate kinase (IPK) family, including yeast Kcs1 and plant IPK1/IPK2 orthologs [2,3,6].
• The reaction is a key step in the synthesis of diphosphoinositol polyphosphates (PP-IPs), which regulate phosphate homeostasis, stress responses, and cell signaling [2,6].
• Mutations in genes encoding this activity, such as maize lpa2 and barley lpa mutants, alter seed phytate content and phosphorus storage [5,7].
• In humans, the orthologous enzyme IP6K1 (inositol hexakisphosphate kinase 1) produces 5-PP-IP5, which has been implicated in insulin signaling, cancer, and neurological processes [1,6].
• Studying GO:0000832 requires biochemical assays, genetic knockouts, and CRISPR-based models to dissect its role in health and disease [2,5,6].
Description
Inositol hexakisphosphate 5-kinase activity (GO:0000832) is a molecular function that catalyzes the phosphorylation of 1D-myo-inositol hexakisphosphate (IP6) at the 5-position, yielding 5-diphospho-1D-myo-inositol 1,2,3,4,6-pentakisphosphate (5-PP-IP5) and ADP. This reaction is part of the higher inositol polyphosphate metabolic pathway, which generates diphosphoinositol polyphosphates (PP-IPs) that serve as signaling molecules and phosphate reservoirs [2,6]. The activity was first molecularly defined in Saccharomyces cerevisiae through the identification of Kcs1, a kinase that synthesizes diphosphoinositol pentakisphosphate. Since then, orthologous enzymes have been characterized in plants, where they influence seed phytate accumulation and phosphorus homeostasis [3,5,7]. In mammals, the enzyme IP6K1 (inositol hexakisphosphate kinase 1) carries out this activity and has been linked to diverse cellular processes, including insulin secretion, DNA repair, and cancer progression [1,6]. Understanding GO:0000832 is therefore critical for researchers studying inositol phosphate signaling, metabolic disorders, and agricultural traits.
inositol hexakisphosphate 5-kinase activity At A Glance
| GO ID | GO:0000832 |
|---|---|
| GO term | inositol hexakisphosphate 5-kinase activity |
| Ontology | molecular_function |
| Synonym | ATP:1D-myo-inositol-hexakisphosphate 5-phosphotransferase activity |
| Major function | Phosphorylation of IP6 to 5-PP-IP5 using ATP |
| Reaction | 1D-myo-inositol hexakisphosphate + ATP = 5-diphospho-1D-myo-inositol 1,2,3,4,6-pentakisphosphate + ADP |
| Substrates | 1D-myo-inositol hexakisphosphate (IP6), ATP |
| Products | 5-diphospho-1D-myo-inositol 1,2,3,4,6-pentakisphosphate (5-PP-IP5), ADP |
| Enzyme family | Inositol polyphosphate kinase (IPK) family |
| Representative genes | KCS1 (yeast), IPK1 (plants), IP6K1 (human) |
What Is GO:0000832?
GO:0000832, inositol hexakisphosphate 5-kinase activity, is defined as the catalysis of the reaction: 1D-myo-inositol hexakisphosphate + ATP = 5-diphospho-1D-myo-inositol 1,2,3,4,6-pentakisphosphate + ADP. In other words, it is the enzyme activity that transfers a phosphate group from ATP to the 5-position of IP6, producing a diphosphorylated inositol pentakisphosphate (5-PP-IP5). This activity belongs to the molecular_function ontology and is synonymous with ATP:1D-myo-inositol-hexakisphosphate 5-phosphotransferase activity.
Why Is inositol hexakisphosphate 5-kinase activity Important in Cell Biology?
GO:0000832 is important because it represents a committed step in the synthesis of diphosphoinositol polyphosphates, which are emerging as key regulators of cellular phosphate homeostasis, stress responses, and signaling pathways [2,6]. In plants, this activity affects seed phytate content, a major determinant of nutritional quality and phosphorus utilization [3,5,7]. In humans, the enzyme IP6K1, which catalyzes this reaction, has been implicated in insulin signaling, cancer, and neurological disorders, making it a potential therapeutic target [1,6]. Thus, understanding GO:0000832 provides insights into fundamental biology and offers translational opportunities.
• Regulates synthesis of diphosphoinositol polyphosphates (PP-IPs), which act as signaling molecules and phosphate donors.
• Controls seed phytate accumulation in crops, affecting nutritional value and phosphorus pollution [5,7].
• Modulates insulin secretion and glucose homeostasis in mammals.
• Plays a role in DNA repair and genome stability through PP-IP synthesis.
• Influences stress responses and phosphate starvation signaling in yeast and plants [2,3].
• Associated with cancer cell proliferation and survival in human studies.
• Provides a target for engineering low-phytate crops to improve micronutrient bioavailability [5,7].
• Serves as a model for studying inositol polyphosphate kinase family evolution and function [2,3].
What Happens During inositol hexakisphosphate 5-kinase activity?
Substrate binding and recognition
In simple terms: The enzyme grabs IP6 and ATP to start the reaction.
The enzyme binds its substrate, 1D-myo-inositol hexakisphosphate (IP6), and the phosphate donor ATP. Structural and biochemical studies on yeast Kcs1 and plant IPK1 have shown that these enzymes specifically recognize the fully phosphorylated inositol ring and ATP, positioning the 5-hydroxyl group for phosphorylation [2,3,6].
Phosphoryl transfer
In simple terms: A phosphate group is moved from ATP to IP6.
The enzyme catalyzes the transfer of the gamma-phosphate from ATP to the 5-position of IP6, forming 5-diphospho-1D-myo-inositol 1,2,3,4,6-pentakisphosphate (5-PP-IP5) and ADP. This reaction is magnesium-dependent and follows an in-line transfer mechanism typical of phosphotransferases.
Product release and downstream metabolism
In simple terms: The new molecule 5-PP-IP5 is released and can be used in other pathways.
After catalysis, 5-PP-IP5 is released and can serve as a substrate for further phosphorylation or as a signaling molecule. In yeast, 5-PP-IP5 can be converted to other diphosphoinositol polyphosphates, contributing to phosphate homeostasis and stress responses [2,6].
Regulation by cellular cues
In simple terms: The activity can be turned up or down by cellular signals.
The activity of inositol hexakisphosphate 5-kinase is regulated by the availability of IP6 and ATP, as well as by cellular phosphate status. In plants, expression of IPK1 is modulated during seed development, affecting phytate accumulation [3,5,7].
Key Genes Involved in GO:0000832 inositol hexakisphosphate 5-kinase activity
The following genes and proteins are known to carry or regulate inositol hexakisphosphate 5-kinase activity across model organisms.
| Gene | Major Role | Research Relevance |
|---|---|---|
| KCS1 (S. cerevisiae) | Inositol hexakisphosphate 5-kinase; synthesizes 5-PP-IP5 | First identified enzyme for this activity; model for PP-IP signaling |
| IPK1 (Arabidopsis thaliana) | Inositol polyphosphate 6-/3-/5-kinase; produces IP6 and PP-IPs | Regulates seed phytate and phosphate homeostasis |
| IPK2 (Arabidopsis thaliana) | Inositol polyphosphate 6-/3-/5-kinase | Involved in inositol phosphate metabolism |
| IP6K1 (Homo sapiens) | Inositol hexakisphosphate kinase 1; produces 5-PP-IP5 | Implicated in insulin signaling, cancer, and DNA repair [1,6] |
| IP6K2 (Homo sapiens) | Inositol hexakisphosphate kinase 2 | Potential role in cell survival and stress responses |
| IP6K3 (Homo sapiens) | Inositol hexakisphosphate kinase 3 | Expressed in brain; may affect neuronal signaling |
| LPA2 (Zea mays) | Inositol phosphate kinase; low phytic acid mutant | Affects seed phytate and phosphorus content |
| LPA (Hordeum vulgare) | Inositol phosphate kinase; low phytic acid | Alters seed phosphorus and inositol phosphate phenotype |
| ITPK1 (Homo sapiens) | Inositol-tetrakisphosphate 1-kinase | Can phosphorylate IP6? (not directly 5-kinase) |
| IPMK (Homo sapiens) | Inositol polyphosphate multikinase | Produces IP5 and IP6 precursors |
| PLC (various) | Phospholipase C; generates IP3 | Upstream of inositol phosphate pathway |
| IP3K (S. cerevisiae) | Inositol 1,4,5-trisphosphate 3-kinase | Initiates a novel inositol polyphosphate pathway |
| PPIP5K (Homo sapiens) | Diphosphoinositol pentakisphosphate kinase | Further phosphorylates 5-PP-IP5 |
| DIPP (Homo sapiens) | Diphosphoinositol polyphosphate phosphohydrolase | Degrades PP-IPs, opposing 5-kinase activity |
| VIP1 (S. cerevisiae) | Inositol hexakisphosphate kinase | Vacuolar transporter chaperone; regulates PP-IP synthesis |
| KCS1 (S. pombe) | Inositol hexakisphosphate kinase | Fission yeast model for PP-IP functions |
How Is inositol hexakisphosphate 5-kinase activity Regulated?
The activity of inositol hexakisphosphate 5-kinase is regulated at multiple levels. In yeast, Kcs1 activity is influenced by phosphate availability and the cellular energy status, as it requires ATP [2,6]. In plants, IPK1 expression is developmentally regulated during seed maturation, affecting phytate accumulation [3,5,7]. In mammals, IP6K1 activity can be modulated by post-translational modifications and interacting proteins, although the precise mechanisms are still under investigation [1,6]. Additionally, the product 5-PP-IP5 can be further metabolized by PPIP5K or degraded by DIPP enzymes, providing a layer of regulation.
inositol hexakisphosphate 5-kinase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| IP6K1 | Cancer, insulin resistance | Knockout mice, cancer cell lines |
| IP6K2 | Cell survival, stress response | CRISPR knockout in HeLa cells |
| IP6K3 | Neurological disorders | Neuronal cell lines, knockout mice |
| LPA2 (maize) | Low phytic acid seed trait | Maize mutants, transgenic plants |
| LPA (barley) | Low phytic acid seed trait | Barley mutants, field trials |
Cancer
IP6K1, the human enzyme with inositol hexakisphosphate 5-kinase activity, has been implicated in cancer cell proliferation and survival. Studies suggest that 5-PP-IP5 produced by IP6K1 may influence signaling pathways that promote tumor growth, making it a potential target for cancer therapy [1,6].
Metabolic disorders
IP6K1 is involved in insulin secretion and glucose homeostasis. Dysregulation of its activity has been linked to type 2 diabetes and metabolic syndrome, highlighting the importance of GO:0000832 in metabolic health.
Neurological disorders
Inositol polyphosphates, including 5-PP-IP5, are abundant in the brain and have been implicated in neuronal signaling and neurodegeneration. Altered IP6K1 activity may contribute to conditions such as Alzheimer's disease, though further research is needed.
From inositol hexakisphosphate 5-kinase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does knockout of IP6K1 reduce 5-PP-IP5 levels? | CRISPR knockout in HEK293 or HeLa cells |
| What is the effect of a point mutation in the catalytic site? | Point-mutation knock-in in yeast Kcs1 |
| How does overexpression of IP6K1 affect insulin secretion? | Overexpression in pancreatic beta cells |
| Can tagged IP6K1 be used to study localization? | Knock-in of GFP tag in human cells |
| Does IPK1 knockout alter seed phytate? | CRISPR knockout in Arabidopsis or maize |
| What is the role of Kcs1 in phosphate homeostasis? | Yeast knockout and complementation |
How to Study the inositol hexakisphosphate 5-kinase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| In vitro kinase assay | Enzymatic activity | Validation of enzyme function |
| LC-MS/MS | Inositol polyphosphate levels | Metabolic profiling |
| CRISPR knockout | Loss-of-function phenotype | Gene function studies |
| CRISPR point mutation | Effect of specific amino acid changes | Catalytic mechanism |
| CRISPR knock-in | Tagged protein localization | Live-cell imaging |
| Overexpression | Gain-of-function effects | Signaling studies |
| RNA-seq | Transcriptional changes | Pathway analysis |
| Phosphate flux assay | Phosphate homeostasis | Plant and yeast studies |
Biochemical kinase assays
In vitro kinase assays using recombinant enzymes and radiolabeled ATP are the gold standard to measure inositol hexakisphosphate 5-kinase activity. These assays quantify the conversion of IP6 to 5-PP-IP5 and are used to validate enzyme function and inhibitor effects.
Genetic knockouts and phenotypic analysis
Knockout models in yeast, plants, and mammalian cells have been used to study the physiological consequences of losing this activity. For example, yeast kcs1 mutants show reduced PP-IP levels and altered phosphate metabolism [2,6].
Mass spectrometry-based metabolomics
LC-MS/MS can quantify inositol polyphosphates, including IP6 and 5-PP-IP5, in cell extracts. This method is essential for profiling changes in the pathway under different conditions.
CRISPR-based genome editing
CRISPR-Cas9 is used to generate knockout, point-mutation, and knock-in models to dissect the function of genes encoding this activity. These models enable precise genetic studies in various organisms [2,5].
How CRISPR Can Be Used to Study GO:0000832 inositol hexakisphosphate 5-kinase activity
Knockout
CRISPR knockout of genes encoding inositol hexakisphosphate 5-kinase activity, such as KCS1 in yeast or IP6K1 in human cells, allows researchers to study the loss-of-function phenotype. These models have revealed roles in phosphate homeostasis, stress responses, and insulin signaling [2,6].
Point Mutation
Introducing point mutations in the catalytic domain of the enzyme can help identify essential residues for substrate binding and catalysis. For example, mutating the ATP-binding lysine in Kcs1 abolishes kinase activity, providing insights into the mechanism.
Knock-in
Knock-in of epitope tags or fluorescent proteins at the endogenous locus enables real-time tracking of enzyme localization and dynamics. This approach has been used to study IP6K1 trafficking in mammalian cells.
Overexpression
Overexpression of the enzyme or its mutants can amplify the pathway and reveal gain-of-function effects. In plants, overexpression of IPK1 increases phytate content, while overexpression of IP6K1 in beta cells enhances insulin secretion [1,3].
How EDITGENE Supports inositol hexakisphosphate 5-kinase activity Research
Researchers studying inositol hexakisphosphate 5-kinase activity-related genes often need to determine whether a candidate gene is causally involved in a specific biological process or disease. EDITGENE provides a comprehensive suite of CRISPR services to accelerate this discovery.
Contact EDITGENE today to design your custom CRISPR model for inositol hexakisphosphate 5-kinase activity research.
Related Products
| Product name | Cat.No. | Species | Gene ID | |
|---|---|---|---|---|
| IP6K3 Knockout HEK293 Cell Line | EDJ-KQ1031 | Human | 117283 | Details Get a Quote |
| IP6K1 Knockout HEK293 Cell Line | EDJ-KQ1685 | Human | 9807 | Details Get a Quote |
| IP6K2 Knockout HEK293 Cell Line | EDJ-KQ1686 | Human | 51447 | Details Get a Quote |
| PPIP5K2 Knockout HEK293 Cell Line | EDJ-KQ1687 | Human | 23262 | Details Get a Quote |
| IP6K1 Knockout A-549 Cell Line | EDJ-KQ21474 | Human | 9807 | Details Get a Quote |
| IP6K1 Knockout HCT 116 Cell Line | EDJ-KQ21475 | Human | 9807 | Details Get a Quote |
| IP6K1 Knockout HeLa Cell Line | EDJ-KQ21476 | Human | 9807 | Details Get a Quote |
| IP6K2 Knockout A-549 Cell Line | EDJ-KQ21477 | Human | 51447 | Details Get a Quote |
| IP6K2 Knockout HCT 116 Cell Line | EDJ-KQ21478 | Human | 51447 | Details Get a Quote |
| IP6K2 Knockout HeLa Cell Line | EDJ-KQ21479 | Human | 51447 | Details Get a Quote |
| PPIP5K2 Knockout A-549 Cell Line | EDJ-KQ21481 | Human | 23262 | Details Get a Quote |
| PPIP5K2 Knockout HCT 116 Cell Line | EDJ-KQ21482 | Human | 23262 | Details Get a Quote |
| PPIP5K2 Knockout HeLa Cell Line | EDJ-KQ21483 | Human | 23262 | Details Get a Quote |
| PPIP5K1 Knockout HEK293 Cell Line | EDJ-KQ50893 | Human | 9677 | Details Get a Quote |
| PPIP5K1 Knockout HeLa Cell Line | EDJ-KQ55224 | Human | 9677 | Details Get a Quote |
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Frequently Asked Questions About inositol hexakisphosphate 5-kinase activity
What is inositol hexakisphosphate 5-kinase activity?
It is the enzyme activity that phosphorylates IP6 to 5-PP-IP5 using ATP, encoded by GO:0000832.
What genes are involved in inositol hexakisphosphate 5-kinase activity?
Key genes include KCS1 in yeast, IPK1 in plants, and IP6K1, IP6K2, IP6K3 in humans [1,2,3,6].
What is the reaction catalyzed by GO:0000832?
1D-myo-inositol hexakisphosphate + ATP = 5-diphospho-1D-myo-inositol 1,2,3,4,6-pentakisphosphate + ADP.
How is inositol hexakisphosphate 5-kinase activity regulated?
It is regulated by substrate availability, cellular phosphate status, and developmental cues [2,3,6].
What diseases are associated with inositol hexakisphosphate 5-kinase activity?
It has been linked to cancer, metabolic disorders, and neurological conditions through IP6K1 [1,6].
What model organisms are used to study GO:0000832?
Yeast, plants (Arabidopsis, maize, barley), and mammalian cell lines are commonly used [2,3,5,6,7].
How can CRISPR be used to study inositol hexakisphosphate 5-kinase activity?
CRISPR can create knockouts, point mutations, knock-ins, and overexpression models to dissect gene function [2,5,6].
What methods measure inositol hexakisphosphate 5-kinase activity?
In vitro kinase assays, LC-MS/MS, and genetic phenotypic analyses are standard.
Is IP6K1 the human enzyme for GO:0000832?
Yes, IP6K1 catalyzes the 5-kinase activity on IP6 to produce 5-PP-IP5 [1,6].
Why is inositol hexakisphosphate 5-kinase activity important for agriculture?
It affects seed phytate content, which impacts nutritional quality and phosphorus management [5,7].
Conclusion
Inositol hexakisphosphate 5-kinase activity (GO:0000832) is a critical enzymatic function in the inositol polyphosphate pathway, with roles in phosphate homeostasis, signaling, and disease. Its study spans yeast, plants, and mammals, offering insights into fundamental biology and potential therapeutic targets. EDITGENE provides advanced CRISPR tools to accelerate research on this activity and its associated genes.
References
- 1. Downes CP et al.. 1990. myo-inositol metabolites as cellular signals.. Eur J Biochem 193(1):1-18 PMID: 2171926
- 2. Seeds AM et al.. 2005. Molecular definition of a novel inositol polyphosphate metabolic pathway initiated by inositol 1,4,5-trisphosphate 3-kinase activity in Saccharomyces cerevisiae.. J Biol Chem 280(30):27654-61 PMID: 15944147
- 3. Stevenson-Paulik J et al.. 2002. Molecular and biochemical characterization of two plant inositol polyphosphate 6-/3-/5-kinases.. J Biol Chem 277(45):42711-8 PMID: 12226109
- 5. Shi J et al.. 2003. The maize low-phytic acid mutant lpa2 is caused by mutation in an inositol phosphate kinase gene.. Plant Physiol 131(2):507-15 PMID: 12586875
- 6. Saiardi A et al.. 1999. Synthesis of diphosphoinositol pentakisphosphate by a newly identified family of higher inositol polyphosphate kinases.. Curr Biol 9(22):1323-6 PMID: 10574768
- 7. Dorsch JA et al.. 2003. Seed phosphorus and inositol phosphate phenotype of barley low phytic acid genotypes.. Phytochemistry 62(5):691-706 PMID: 12620321
