GO:0035299 inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0035299 defines the enzyme activity that converts 1D-myo-inositol 1,3,4,5,6-pentakisphosphate (IP5) to 1D-myo-inositol hexakisphosphate (IP6) using ATP.
• The enzyme is known as IP5 2-kinase or IPK1 and is conserved from plants to mammals.
• Its catalytic mechanism involves conformational changes and a strict preference for the myo-inositol enantiomer.
• In rice, a 33-nt deletion in the IPK1 gene enhances tolerance to salt and drought stress, linking the enzyme to abiotic stress responses.
• Mammalian IPK1 contains a zinc-binding site that is important for protein function.
• Studying GO:0035299 helps researchers understand inositol polyphosphate signaling, stress adaptation, and potential disease connections.
Description
Inositol polyphosphates are ubiquitous signaling molecules involved in diverse cellular processes, including chromatin remodeling, mRNA export, and stress responses. The final step in the synthesis of the most abundant inositol polyphosphate, inositol hexakisphosphate (IP6), is catalyzed by inositol-1,3,4,5,6-pentakisphosphate 2-kinase (IP5 2-kinase), encoded by the IPK1 gene. This enzyme transfers a phosphate group from ATP to the 2-position of 1D-myo-inositol 1,3,4,5,6-pentakisphosphate (IP5), yielding IP6 and ADP. The reaction is essential for producing IP6, which serves as a precursor for higher inositol pyrophosphates and as a regulator of various cellular functions. Because IP6 is involved in many physiological and pathological processes, understanding the regulation and mechanism of IP5 2-kinase is of broad interest. The enzyme has been purified from plant sources such as immature soybean seeds, and its crystal structure has been solved from both mammalian and fungal sources. These studies have revealed key features such as a two-lobed architecture, substrate-induced conformational changes, and a zinc-binding site in the mammalian enzyme. In plants, mutations in IPK1 can alter stress tolerance, as shown by a rice mutant with enhanced salt and drought tolerance. Thus, GO:0035299 represents a critical enzymatic activity at the intersection of inositol metabolism, signaling, and stress adaptation.
inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity At A Glance
| GO ID | GO:0035299 |
|---|---|
| GO term | inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity |
| Ontology | molecular_function |
| Synonym | inositol hexakisphosphate synthase, inositol pentakisphosphate 2-kinase activity, inositol-pentakisphosphate 2-kinase activity, inositol polyphosphate kinase activity, Ins(1,3,4,5,6)P5 2-kinase activity, IP5 2-kinase activity |
| Major function | Catalyzes the phosphorylation of IP5 to IP6 using ATP |
| Reaction | 1D-myo-inositol 1,3,4,5,6-pentakisphosphate + ATP = 1D-myo-inositol hexakisphosphate + ADP + H+ |
| Enzyme class | Kinase (phosphotransferase) |
| Substrate specificity | Strict preference for the myo-inositol enantiomer of IP5 |
| Cofactors | ATP; mammalian enzyme contains a zinc-binding site |
What Is GO:0035299?
GO:0035299, inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity, is a molecular function defined as the catalysis of the reaction: 1D-myo-inositol 1,3,4,5,6-pentakisphosphate + ATP = 1D-myo-inositol hexakisphosphate + ADP + H+. In other words, it is the enzyme activity that adds a phosphate group to the 2-position of IP5 to produce IP6, using ATP as the phosphate donor.
Why Is inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity Important in Cell Biology?
GO:0035299 is important because it catalyzes the final step in the biosynthesis of inositol hexakisphosphate (IP6), a molecule that plays critical roles in cellular signaling, stress responses, and development. IP6 is a precursor for inositol pyrophosphates, which regulate processes such as vesicle trafficking, DNA repair, and telomere maintenance. The enzyme is conserved across eukaryotes, and its activity affects plant stress tolerance and potentially human health. Understanding its mechanism and regulation can inform strategies for crop improvement and therapeutic development.
• IP6 produced by this enzyme is a key signaling molecule involved in many cellular processes.
• In plants, IPK1 mutations can enhance tolerance to salt and drought stress.
• The enzyme is conserved from plants to mammals, making it a model for studying inositol polyphosphate synthesis.
• Mammalian IPK1 has a unique zinc-binding site that is important for its function.
• Substrate-induced conformational changes are critical for catalysis and substrate selectivity.
• IP6 and its derivatives are implicated in cancer, diabetes, and neurodegenerative diseases, though direct links require further study.
• The enzyme is a potential target for modulating inositol polyphosphate levels in cells.
• Studying GO:0035299 helps understand the evolution of inositol kinases and their regulation.
• Crystal structures of IPK1 from different organisms provide insights into drug design.
• The rice ipk1 mutant demonstrates the potential for genetic improvement of stress tolerance.
Molecular Mechanism of inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity
Substrate Binding and Conformational Changes
In simple terms: The enzyme changes shape when it grabs its substrate, which helps it work properly.
IP5 2-kinase binds its substrate, 1D-myo-inositol 1,3,4,5,6-pentakisphosphate (IP5), in a specific pocket. Upon binding, the enzyme undergoes conformational changes, particularly in the N-terminal lobe, which are essential for catalysis. These changes facilitate the correct positioning of the substrate and the ATP molecule for phosphate transfer.
Catalytic Mechanism and Phosphate Transfer
In simple terms: The enzyme takes a phosphate from ATP and attaches it to IP5 to make IP6.
The catalytic mechanism involves the transfer of the gamma-phosphate from ATP to the 2-position of IP5, resulting in the formation of IP6 and ADP. The reaction requires magnesium ions as cofactors. The enzyme exhibits strict enantiomeric preference, acting only on the myo-inositol form of IP5.
Role of the Zinc-Binding Site in Mammalian IPK1
In simple terms: A zinc ion helps the mammalian enzyme maintain its structure and function.
The crystal structure of mammalian IP5 2-kinase revealed a novel zinc-binding site that is not present in plant or fungal homologs. This zinc site is important for protein stability and function, and mutations in the zinc-coordinating residues reduce enzyme activity.
Substrate Selectivity and Regulation
In simple terms: The enzyme is picky about which molecule it acts on, and its activity can be controlled.
IP5 2-kinase is highly specific for IP5 and does not phosphorylate other inositol polyphosphates. The enzyme's activity can be regulated by its conformational stability and possibly by post-translational modifications, though specific regulatory mechanisms are still being investigated.
Key Genes Involved in GO:0035299 inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity
The following genes and proteins are directly involved in or closely related to inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity (GO:0035299).
| Gene | Major Role | Research Relevance |
|---|---|---|
| IPK1 (human) | Encodes inositol-pentakisphosphate 2-kinase | Catalyzes IP5 to IP6 conversion; zinc-binding site |
| IPK1 (mouse) | Ortholog of human IPK1 | Used for structural studies |
| IPK1 (rice) | Encodes IP5 2-kinase in rice | 33-nt deletion enhances salt/drought tolerance |
| IPK1 (soybean) | First purified plant IP5 2-kinase | Biochemical characterization |
| IPK1 (Cryptococcus neoformans) | Fungal IP5 2-kinase | Crystal structure solved |
| IPK1 (Arabidopsis) | Plant IP5 2-kinase | Model for plant inositol signaling |
| IPK2 | Inositol polyphosphate kinase | Produces IP5, substrate for IPK1 |
| IPPK | Inositol-pentakisphosphate 2-kinase | Alternative name for IPK1 in some organisms |
| ITPK1 | Inositol-tetrakisphosphate 1-kinase | Upstream enzyme in inositol phosphate pathway |
| IP6K | Inositol hexakisphosphate kinase | Uses IP6 to produce IP7 |
| PPIP5K | Diphosphoinositol pentakisphosphate kinase | Produces IP8 from IP7 |
| MINPP1 | Multiple inositol polyphosphate phosphatase | Degrades IP6 |
| ATP | Phosphate donor | Required for kinase reaction |
| Mg2+ | Cofactor | Essential for catalysis |
| Zn2+ | Structural cofactor in mammalian IPK1 | Important for protein function |
How Is inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity Regulated?
The activity of inositol-1,3,4,5,6-pentakisphosphate 2-kinase (IPK1) is regulated at multiple levels. In plants, the expression of IPK1 can be induced by abiotic stresses such as salt and drought, as suggested by the enhanced stress tolerance of a rice mutant with a 33-nt deletion in the gene. In mammals, the enzyme's activity is influenced by its conformational stability and the presence of a zinc-binding site, which is critical for function. Substrate availability (IP5 levels) and product feedback (IP6 levels) may also modulate activity, though direct evidence is limited. Further research is needed to fully elucidate the regulatory mechanisms.
inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| IPK1 (human) | Cancer, neurodegenerative diseases | Knockout or point mutation in cancer cell lines |
| IPK1 (rice) | Salt and drought stress tolerance | Rice ipk1 mutant with 33-nt deletion |
| IP6K | Inositol pyrophosphate-related disorders | Overexpression or knockout in mammalian cells |
| MINPP1 | Inositol polyphosphate metabolism disorders | Knockout in cell lines |
| ITPK1 | Inositol signaling in development | Zebrafish or mouse models |
Inositol Polyphosphates and Cancer
IP6, the product of GO:0035299, has been implicated in cancer prevention and treatment, with studies suggesting it can inhibit cell proliferation and induce apoptosis. However, the direct role of IPK1 in cancer remains to be fully established. The enzyme's product, IP6, is a precursor for inositol pyrophosphates, which are involved in DNA repair and telomere maintenance, processes relevant to cancer.
Neurodegenerative Diseases
Inositol polyphosphates are important in neuronal signaling, and dysregulation of their metabolism has been linked to neurodegenerative conditions. IP6 has been shown to interact with proteins involved in Alzheimer's and Parkinson's diseases, though the specific contribution of IPK1 activity requires further investigation.
Plant Stress Tolerance
In rice, a mutation in the IPK1 gene that reduces its activity leads to enhanced tolerance to salt and drought stress. This finding highlights the potential of manipulating GO:0035299 for crop improvement, although the underlying mechanisms are still being studied.
From inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the effect of IPK1 loss on IP6 levels? | Knockout cell lines (e.g., HEK293) generated by CRISPR |
| How does the zinc-binding site mutation affect IPK1 activity? | Point mutation knock-in of zinc-coordinating residues |
| Can IPK1 be tagged for localization studies? | Knock-in of fluorescent protein tag (e.g., GFP) at the endogenous locus |
| What is the effect of IPK1 overexpression on stress tolerance? | Overexpression of IPK1 in plant or mammalian cells |
| How does IPK1 mutation affect inositol polyphosphate profile? | Knockout or point mutation followed by mass spectrometry |
| Can IPK1 be targeted for drug discovery? | Structural studies and high-throughput screening using purified enzyme |
How to Study the inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Kinase assay with radioactive ATP | Enzyme activity | Kinetic characterization of IPK1 |
| HPLC or LC-MS | IP6 production | Quantification of enzyme activity in vitro |
| X-ray crystallography | Three-dimensional structure | Understanding catalytic mechanism |
| Site-directed mutagenesis | Role of specific residues | Identifying key catalytic and binding residues |
| CRISPR knockout | Loss-of-function phenotype | Studying cellular effects of IPK1 deletion |
| CRISPR knock-in | Tagged protein expression | Localization and interaction studies |
| RNA-seq | Transcriptional changes | Global effects of IPK1 mutation |
| Stress tolerance assays | Plant survival under salt/drought | Evaluating ipk1 mutant phenotypes |
Enzymatic Assays
The activity of IP5 2-kinase can be measured using radioactive or non-radioactive kinase assays. Typically, purified enzyme is incubated with IP5 and ATP, and the formation of IP6 is detected by HPLC or mass spectrometry. These assays are used to determine kinetic parameters and substrate specificity.
Structural Biology
X-ray crystallography has been used to solve the structures of IP5 2-kinase from various organisms, including mammals and fungi. These studies reveal the active site architecture, conformational changes upon substrate binding, and the role of specific residues in catalysis.
Mutagenesis and Functional Studies
Site-directed mutagenesis is employed to investigate the roles of specific amino acids in substrate binding and catalysis. For example, mutations in the zinc-binding site of mammalian IPK1 reduce activity, confirming its importance. Such studies help map the functional domains of the enzyme.
Genetic Approaches in Plants
In rice, a 33-nt deletion in the IPK1 gene was identified in a mutant with enhanced salt and drought tolerance. This demonstrates the use of forward genetics to uncover the physiological roles of GO:0035299. Similar approaches can be applied in other crops.
How CRISPR Can Be Used to Study GO:0035299 inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity
Knockout
CRISPR knockout of IPK1 can be used to eliminate enzyme activity and study the consequences on IP6 levels and downstream processes. For example, knockout cell lines can reveal the role of IP6 in cellular signaling and stress responses. In plants, knockout of IPK1 may enhance stress tolerance, as observed in rice.
Point Mutation
Point mutations can be introduced to dissect the catalytic mechanism. For instance, mutating the zinc-coordinating residues in mammalian IPK1 can abolish activity, confirming the importance of the zinc site. Such models help distinguish between structural and catalytic roles of specific amino acids.
Knock-in
Knock-in of a fluorescent tag (e.g., GFP) at the endogenous IPK1 locus allows real-time visualization of the enzyme's localization and dynamics. This approach can also be used to introduce disease-associated mutations or to study the effect of specific post-translational modifications.
Overexpression
Overexpression of IPK1 can increase IP6 levels and may enhance stress tolerance in plants. In mammalian cells, overexpression can be used to study the effects of elevated IP6 on signaling pathways and cellular phenotypes.
How EDITGENE Supports inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity Research
Researchers studying inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity-related genes often need to determine whether a candidate gene is causally involved in a specific cellular process or disease. This requires precise genetic manipulation, which can be achieved through CRISPR-based genome editing. EDITGENE provides a comprehensive suite of services to support such studies, from knockout and point mutation to knock-in and overexpression, as well as library screening and bioinformatics analysis.
Contact EDITGENE today to design your custom CRISPR model for inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity research.
Frequently Asked Questions About inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity
What is inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity?
It is the enzyme activity that converts IP5 to IP6 by adding a phosphate group, encoded by the IPK1 gene.
What genes are involved in inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity?
The primary gene is IPK1, also known as IP5 2-kinase or IPPK. Other genes in the pathway include IPK2, ITPK1, IP6K, and PPIP5K.
What is the GO ID for inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity?
The GO ID is GO:0035299.
What is the reaction catalyzed by IP5 2-kinase?
It catalyzes: 1D-myo-inositol 1,3,4,5,6-pentakisphosphate + ATP = 1D-myo-inositol hexakisphosphate + ADP + H+.
Why is IP5 2-kinase important in plants?
In rice, a mutation in IPK1 enhances salt and drought tolerance, suggesting a role in stress adaptation.
What is the structure of IP5 2-kinase?
It has a two-lobed structure with a zinc-binding site in mammals, and undergoes conformational changes upon substrate binding.
How is IP5 2-kinase regulated?
Regulation occurs at multiple levels, including gene expression under stress and conformational stability.
What diseases are associated with IP5 2-kinase?
IP6, the product, is implicated in cancer and neurodegenerative diseases, but direct links to IPK1 require further study.
Can CRISPR be used to study IP5 2-kinase?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are valuable for studying its function.
What methods are used to measure IP5 2-kinase activity?
Kinase assays with radioactive ATP, HPLC, and mass spectrometry are commonly used.
Conclusion
GO:0035299, inositol-1,3,4,5,6-pentakisphosphate 2-kinase activity, is a critical enzymatic function in the synthesis of IP6, a molecule with diverse roles in cellular signaling and stress responses. Research across plants, fungi, and mammals has revealed conserved mechanisms and unique features such as the mammalian zinc-binding site. Understanding this activity offers insights into basic biology and potential applications in agriculture and medicine. Continued investigation using advanced genetic and biochemical tools will further illuminate its regulation and therapeutic potential.
References
- 1. Jiang M et al.. 2020. An Inositol 1,3,4,5,6-Pentakisphosphate 2-Kinase 1 Mutant with a 33-nt Deletion Showed Enhanced Tolerance to Salt and Drought Stress in Rice.. Plants (Basel) 10(1) PMID: 33374298
- 2. Franco-Echevarría E et al.. 2017. Crystallization and Preliminary X-Ray Diffraction Analysis of a Mammal Inositol 1,3,4,5,6-Pentakisphosphate 2-Kinase.. Protein J 36(4):240-248 PMID: 28429156
- 3. Gosein V et al.. 2013. Conformational stability of inositol 1,3,4,5,6-pentakisphosphate 2-kinase (IPK1) dictates its substrate selectivity.. J Biol Chem 288(52):36788-95 PMID: 24165122
- 4. Oh J et al.. 2017. Crystal structure of inositol 1,3,4,5,6-pentakisphosphate 2-kinase from Cryptococcus neoformans.. J Struct Biol 200(2):118-123 PMID: 28919350
- 5. Phillippy BQ et al.. 1994. Purification and some properties of inositol 1,3,4,5,6-Pentakisphosphate 2-kinase from immature soybean seeds.. J Biol Chem 269(45):28393-9 PMID: 7961779
- 6. Baños-Sanz JI et al.. 2012. Conformational changes in inositol 1,3,4,5,6-pentakisphosphate 2-kinase upon substrate binding: role of N-terminal lobe and enantiomeric substrate preference.. J Biol Chem 287(35):29237-49 PMID: 22745128
- 7. Franco-Echevarría E et al.. 2017. 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.. J Biol Chem 292(25):10534-10548 PMID: 28450399
- 8. Gosein V et al.. 2013. Roles of phosphate recognition in inositol 1,3,4,5,6-pentakisphosphate 2-kinase (IPK1) substrate binding and activation.. J Biol Chem 288(37):26908-13 PMID: 23884422
