GO:0047130 saccharopine dehydrogenase (NADP+, L-lysine-forming) activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0047130 describes the enzyme activity that catalyzes the final step of the saccharopine pathway, converting L-saccharopine to L-lysine and 2-oxoglutarate using NADP+ as a cofactor.
• This activity is distinct from the NAD+-dependent saccharopine dehydrogenase (GO:0004754) and is often referred to as L-lysine-alpha-ketoglutarate reductase, reflecting its reverse reaction.
• The enzyme is localized primarily to mitochondria in mammalian cells, where it participates in lysine catabolism.
• Deficiency or dysregulation of this activity has been linked to metabolic disorders such as hyperlysinemia and potentially to neurological conditions, though direct evidence for GO:0047130 in disease is still emerging [1,2].
• Studying this activity requires careful distinction from other saccharopine dehydrogenases and related enzymes, using specific substrates and cofactors.
• CRISPR-based models (knockout, point mutation, knock-in, overexpression) are powerful tools to dissect the physiological roles of genes encoding this activity [1,2].
Description
Saccharopine dehydrogenase (NADP+, L-lysine-forming) activity, encoded by GO:0047130, is a molecular function that catalyzes the reversible conversion of L-saccharopine to L-lysine and 2-oxoglutarate in the presence of NADP+. This reaction constitutes the final step of the saccharopine pathway, a major route for lysine catabolism in eukaryotes. The enzyme is also known as L-lysine-alpha-ketoglutarate reductase, reflecting its ability to catalyze the reverse reaction, and it is distinct from the NAD+-dependent saccharopine dehydrogenase (GO:0004754) that catalyzes the same overall reaction but with different cofactor specificity. Understanding this activity is crucial for researchers studying amino acid metabolism, mitochondrial function, and related metabolic disorders.
saccharopine dehydrogenase (NADP+, L-lysine-forming) activity At A Glance
| GO ID | GO:0047130 |
|---|---|
| GO term | saccharopine dehydrogenase (NADP+, L-lysine-forming) activity |
| Ontology | molecular_function |
| Synonym | L-lysine-alpha-ketoglutarate reductase activity |
| Major function | Catalyzes the final step of the saccharopine pathway, converting L-saccharopine to L-lysine and 2-oxoglutarate using NADP+ |
| Reaction | L-saccharopine + H2O + NADP+ = 2-oxoglutarate + L-lysine + H+ + NADPH |
| Cofactor | NADP+ (nicotinamide adenine dinucleotide phosphate) |
| Localization | Mitochondria (in mammals) |
| Related activity | Saccharopine dehydrogenase (NAD+, L-lysine-forming) (GO:0004754) |
| Pathway | Lysine degradation (saccharopine pathway) |
What Is GO:0047130?
GO:0047130 is defined as the catalysis of the reaction: L-saccharopine + H2O + NADP+ = 2-oxoglutarate + L-lysine + H+ + NADPH. In other words, it is the enzyme activity that removes the saccharopine moiety from L-saccharopine, releasing free lysine and 2-oxoglutarate while reducing NADP+ to NADPH. This activity is synonymous with L-lysine-alpha-ketoglutarate reductase, which catalyzes the reverse reaction, and with several other names reflecting its substrate and cofactor specificity.
Why Is saccharopine dehydrogenase (NADP+, L-lysine-forming) activity Important in Cell Biology?
GO:0047130 is important because it represents a key enzymatic step in lysine catabolism, a process essential for maintaining amino acid homeostasis and energy production. Dysregulation of this activity can lead to accumulation of saccharopine and other metabolites, which have been implicated in metabolic and neurological disorders. Moreover, the enzyme's dual cofactor specificity and reversible nature make it a fascinating subject for mechanistic studies of dehydrogenase enzymes.
• Critical for lysine catabolism and energy production in mitochondria.
• Defects in the saccharopine pathway can cause hyperlysinemia and related metabolic disorders.
• Provides a model for studying dehydrogenase mechanisms and cofactor specificity.
• Potential target for therapeutic intervention in lysine-related metabolic diseases.
• Helps distinguish between NAD+- and NADP+-dependent saccharopine dehydrogenases in research.
• Relevant to understanding mitochondrial redox balance via NADPH production.
• May play a role in neurological conditions linked to lysine metabolism.
• Useful for evolutionary studies of amino acid metabolism enzymes.
• Enables precise metabolic engineering in biotechnology.
• Facilitates development of diagnostic markers for metabolic disorders.
Molecular Mechanism of saccharopine dehydrogenase (NADP+, L-lysine-forming) activity
Substrate Binding and Orientation
In simple terms: The enzyme grabs L-saccharopine and NADP+ and positions them for reaction.
The enzyme binds L-saccharopine and NADP+ in a ordered manner, with L-saccharopine likely binding first, as deduced from initial rate pH studies. The binding involves specific interactions that orient the substrate for hydride transfer.
Hydride Transfer and NADPH Formation
In simple terms: A hydride ion is moved from the substrate to NADP+, making NADPH.
The catalytic mechanism involves a hydride transfer from the C-1 position of L-saccharopine to the nicotinamide ring of NADP+, resulting in the formation of NADPH and the release of 2-oxoglutarate and L-lysine. pH studies suggest the involvement of a general acid-base catalyst with a pKa of about 6.5.
Product Release and Enzyme Turnover
In simple terms: The products are released, and the enzyme is ready for another round.
After the reaction, NADPH, 2-oxoglutarate, and L-lysine are released from the active site, allowing the enzyme to undergo another catalytic cycle. The order of product release may be sequential, with NADPH leaving last, as inferred from kinetic studies.
Reversibility and L-Lysine-alpha-ketoglutarate Reductase Activity
In simple terms: The enzyme can also run the reaction backwards, making saccharopine from lysine and 2-oxoglutarate.
The enzyme catalyzes the reverse reaction, known as L-lysine-alpha-ketoglutarate reductase activity, which condenses L-lysine and 2-oxoglutarate to form L-saccharopine while oxidizing NADPH. This reversibility is important for regulating lysine levels in mitochondria.
Cofactor Specificity and Regulation
In simple terms: The enzyme prefers NADP+ over NAD+, and its activity can be regulated by cellular conditions.
The enzyme is specific for NADP+ as a cofactor, distinguishing it from the NAD+-dependent saccharopine dehydrogenase. Its activity may be regulated by the availability of substrates and cofactors, as well as by post-translational modifications, though direct evidence for regulation is limited.
Key Genes Involved in GO:0047130 saccharopine dehydrogenase (NADP+, L-lysine-forming) activity
The following genes and proteins are directly or indirectly associated with saccharopine dehydrogenase (NADP+, L-lysine-forming) activity, based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| AASS | Encodes a bifunctional enzyme with saccharopine dehydrogenase and aminoadipate-semialdehyde synthase activities | Mutations cause hyperlysinemia; model for studying saccharopine pathway |
| SCCPDH | Saccharopine dehydrogenase (putative) | May exhibit NADP+-dependent activity; less characterized |
| PIPOX | Pipecolate oxidase | Involved in lysine degradation downstream of saccharopine |
| DHTKD1 | Dehydrogenase E1 and transketolase domain containing 1 | Linked to 2-oxoglutarate dehydrogenase complex; may interact metabolically |
| OGDH | 2-oxoglutarate dehydrogenase | Produces 2-oxoglutarate, a substrate for the reverse reaction |
| GLUD1 | Glutamate dehydrogenase 1 | Links amino acid metabolism to TCA cycle |
| SLC25A21 | Mitochondrial 2-oxodicarboxylate carrier | Transports 2-oxoglutarate across mitochondrial membrane |
| LYS1 | Yeast saccharopine dehydrogenase (NAD+) | Model for studying enzyme evolution |
| LYS9 | Yeast saccharopine dehydrogenase (NADP+) | Direct homolog of GO:0047130 in yeast |
| AASS (isoform 2) | Mitochondrial isoform of AASS | Primary location of saccharopine dehydrogenase activity |
| NADP+ | Cofactor | Essential for catalytic activity |
| L-saccharopine | Substrate | Intermediate in lysine catabolism |
| L-lysine | Product | End product of the forward reaction |
| 2-oxoglutarate | Product | TCA cycle intermediate |
| NADPH | Product | Reducing agent produced |
| Saccharopine dehydrogenase (NAD+) | Related enzyme | Distinct cofactor specificity |
| Aminoadipate-semialdehyde | Downstream metabolite | Further degraded to acetyl-CoA |
| Saccharopine | Pathway intermediate | Accumulates in enzyme deficiency |
How Is saccharopine dehydrogenase (NADP+, L-lysine-forming) activity Regulated?
The activity of saccharopine dehydrogenase (NADP+, L-lysine-forming) is primarily regulated by substrate availability and cellular redox state, as it depends on NADP+ and produces NADPH. In rat liver mitochondria, the enzyme's activity may be influenced by the energy status of the cell, but direct regulatory mechanisms such as phosphorylation or allosteric modulation have not been extensively characterized. Further research is needed to elucidate its regulation.
saccharopine dehydrogenase (NADP+, L-lysine-forming) activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| AASS | Hyperlysinemia | AASS knockout cell line (e.g., HEK293) |
| SCCPDH | Unknown metabolic disorder | SCCPDH overexpression in HeLa cells |
| PIPOX | Hyperpipecolatemia | PIPOX knockout mouse model |
| DHTKD1 | Charcot-Marie-Tooth disease | DHTKD1 point mutation knock-in |
| OGDH | D-2-hydroxyglutaric aciduria | OGDH knockdown in neurons |
Hyperlysinemia and Metabolic Disorders
Deficiency in saccharopine dehydrogenase (NADP+, L-lysine-forming) activity, often due to mutations in the AASS gene, can lead to hyperlysinemia, characterized by elevated lysine levels and potentially neurological symptoms. The accumulation of saccharopine may also contribute to metabolic imbalances.
Neurological Implications
Disorders of lysine metabolism, including those involving saccharopine dehydrogenase, have been associated with neurological abnormalities such as developmental delay and seizures, though the exact mechanisms remain unclear. The enzyme's role in mitochondrial metabolism suggests a link to energy homeostasis in neurons.
Potential Role in Cancer Metabolism
Altered lysine catabolism, including saccharopine dehydrogenase activity, may support cancer cell proliferation by providing NADPH and other metabolites, but direct evidence is limited. Further studies are needed to establish a definitive link.
From saccharopine dehydrogenase (NADP+, L-lysine-forming) activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the effect of AASS knockout on lysine levels? | AASS knockout HEK293 cells |
| How does a point mutation in the active site affect catalysis? | Point mutation (e.g., His to Ala) in recombinant enzyme |
| Can we tag the enzyme to study localization? | Knock-in of FLAG tag at endogenous locus |
| What happens when the enzyme is overexpressed? | Overexpression in COS-7 cells |
| Does the enzyme interact with other metabolic proteins? | Knock-in of BirA tag for proximity labeling |
| How does NADP+ binding affect conformation? | Knock-in of fluorescent reporter |
How to Study the saccharopine dehydrogenase (NADP+, L-lysine-forming) activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Spectrophotometric assay | NADPH production | Enzyme kinetics |
| LC-MS metabolomics | Lysine, saccharopine, 2-oxoglutarate levels | Pathway flux analysis |
| Western blot | Protein expression | Knockout validation |
| Immunoprecipitation | Protein interactions | Complex identification |
| CRISPR screen | Gene essentiality | Regulator discovery |
| RNA-seq | Transcriptional changes | Pathway adaptation |
| Fluorescence microscopy | Subcellular localization | Mitochondrial targeting |
Enzymatic Assays
Direct measurement of saccharopine dehydrogenase activity using spectrophotometric assays that monitor NADPH production at 340 nm is the gold standard. These assays require purified enzyme or cell lysates and specific substrates.
Metabolomics
Mass spectrometry-based metabolomics can quantify lysine, saccharopine, and 2-oxoglutarate levels in cells or tissues, providing insights into pathway flux. This method is useful for validating knockout or overexpression models.
Proteomics and Western Blotting
Western blotting with antibodies against AASS or tagged versions of the enzyme can assess protein expression and post-translational modifications. Proteomics can identify interaction partners.
CRISPR Screening
Genome-wide CRISPR screens can identify genes that modulate saccharopine dehydrogenase activity or lysine sensitivity, revealing novel regulators. This approach is powerful for uncovering genetic interactions.
How CRISPR Can Be Used to Study GO:0047130 saccharopine dehydrogenase (NADP+, L-lysine-forming) activity
Knockout
CRISPR knockout of AASS or SCCPDH can abolish saccharopine dehydrogenase activity, leading to lysine accumulation and providing a model for hyperlysinemia. These models are useful for studying metabolic rewiring.
Point Mutation
Introducing point mutations in the active site of the enzyme (e.g., catalytic residues) via CRISPR can dissect the mechanism and identify essential amino acids. Such models help validate in vitro findings.
Knock-in
Knock-in of epitope tags (e.g., FLAG, HA) at the endogenous locus allows for studying protein localization, interactions, and dynamics without overexpression artifacts. This is valuable for understanding the enzyme's role in mitochondria.
Overexpression
CRISPR activation (CRISPRa) or cDNA overexpression can increase enzyme levels, enabling studies of gain-of-function effects and metabolic flux. Overexpression models are useful for drug screening.
How EDITGENE Supports saccharopine dehydrogenase (NADP+, L-lysine-forming) activity Research
Researchers studying saccharopine dehydrogenase (NADP+, L-lysine-forming) activity-related genes often need to determine whether a candidate gene is causally involved in metabolic pathways or disease. EDITGENE provides comprehensive CRISPR services to create precise cellular models for such investigations.
Contact EDITGENE today to design your custom CRISPR model for saccharopine dehydrogenase (NADP+, L-lysine-forming) activity research.
Frequently Asked Questions About saccharopine dehydrogenase (NADP+, L-lysine-forming) activity
What is saccharopine dehydrogenase (NADP+, L-lysine-forming) activity?
It is an enzyme activity that catalyzes the conversion of L-saccharopine to L-lysine and 2-oxoglutarate using NADP+ as a cofactor, encoded by GO:0047130.
What genes are involved in saccharopine dehydrogenase (NADP+, L-lysine-forming) activity?
The primary gene is AASS, which encodes a bifunctional enzyme with this activity; other genes like SCCPDH may also contribute.
What is the difference between GO:0047130 and GO:0004754?
GO:0047130 uses NADP+ as a cofactor, while GO:0004754 uses NAD+; they catalyze similar reactions but are distinct enzymes.
Where is saccharopine dehydrogenase (NADP+, L-lysine-forming) located in the cell?
In mammals, it is primarily localized to mitochondria.
What diseases are associated with saccharopine dehydrogenase deficiency?
Deficiency can cause hyperlysinemia, and may be linked to neurological symptoms.
How can I measure saccharopine dehydrogenase (NADP+, L-lysine-forming) activity?
Spectrophotometric assays monitoring NADPH production at 340 nm are commonly used.
What is the reverse reaction of saccharopine dehydrogenase (NADP+, L-lysine-forming)?
The reverse reaction is L-lysine-alpha-ketoglutarate reductase activity, which forms saccharopine from lysine and 2-oxoglutarate.
Can CRISPR be used to study saccharopine dehydrogenase (NADP+, L-lysine-forming) activity?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are valuable for dissecting its function.
What are the substrates and products of GO:0047130?
Substrates: L-saccharopine, H2O, NADP+; products: 2-oxoglutarate, L-lysine, H+, NADPH.
Is saccharopine dehydrogenase (NADP+, L-lysine-forming) activity regulated?
It is primarily regulated by substrate availability and cellular redox state, but detailed mechanisms are not fully understood.
Conclusion
Saccharopine dehydrogenase (NADP+, L-lysine-forming) activity (GO:0047130) is a key enzymatic function in lysine catabolism, with important implications for metabolic disorders and mitochondrial function. Understanding its mechanism and regulation requires precise experimental models, which can be efficiently generated using CRISPR technologies. EDITGENE offers a suite of services to support such research, from knockout to overexpression and screening.
References
- 1. Fujioka M. 1984. Chemical mechanism of saccharopine dehydrogenase (NAD+, L-lysine-forming) as deduced from initial rate pH studies.. Arch Biochem Biophys 230(2):553-9 PMID: 6712252
- 2. Noda C et al.. 1978. Purification and properties of L-lysine-alpha-ketoglutarate reductase from rat liver mitochondria.. Biochim Biophys Acta 525(2):307-13 PMID: 687635
