GO:0050241 pyrroline-2-carboxylate reductase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0050241 (pyrroline-2-carboxylate reductase activity) catalyzes the reversible NAD(P)H-dependent reduction of 1-pyrroline-2-carboxylate to L-proline.
• The enzyme belongs to a distinct family of NAD(P)H-dependent oxidoreductases and is structurally related to ornithine cyclodeaminase and mu-crystallin.
• In bacteria, it participates in the catabolism of D-lysine, D-proline, and trans-3-hydroxy-L-proline, linking amino acid degradation to central metabolism [1,3].
• In mammals, the activity is enriched in specific brain regions and is implicated in L-pipecolate formation and cerebral ketimine metabolism [2,8].
• The enzyme is a potential biocatalyst for producing homochiral 2-hydroxy-4-butyrolactone derivatives and other chiral intermediates.
• CRISPR-based knockout, point-mutation, and knock-in models enable causal dissection of GO:0050241 in microbial and mammalian systems.
Description
Pyrroline-2-carboxylate reductase activity (GO:0050241) is a molecular function defined by the reversible NAD(P)H-dependent reduction of 1-pyrroline-2-carboxylate to L-proline, with concomitant oxidation of NAD(P)H to NAD(P)+. This activity sits at the intersection of amino acid catabolism and proline homeostasis, and it has been characterized in bacteria, archaea, and mammals [1,2,3,4]. The enzyme is particularly notable for its broad substrate tolerance, acting on cyclic imines such as Delta1-pyrroline-2-carboxylate and Delta1-piperideine-2-carboxylate, which are intermediates in D-proline and D-lysine degradation. Researchers study GO:0050241 because it connects microbial amino acid catabolism to central metabolic pathways and because its mammalian homologs, including mu-crystallin, are implicated in cerebral ketimine metabolism and thyroid hormone regulation. The enzyme also serves as a model for understanding the stereochemistry and conformational dynamics of NAD(P)H-dependent oxidoreductases. In biotechnology, its ability to reduce cyclic imines makes it a candidate for biocatalytic synthesis of chiral lactones and other high-value compounds. Despite its importance, the physiological roles of GO:0050241 in different organisms remain incompletely defined. This article synthesizes the QuickGO definition with verified literature to provide a research-grade overview of the mechanism, genes, disease links, and experimental methods relevant to this activity.
pyrroline-2-carboxylate reductase activity At A Glance
| GO ID | GO:0050241 |
|---|---|
| GO term | pyrroline-2-carboxylate reductase activity |
| Ontology | molecular_function |
| Synonym | delta1-pyrroline-2-carboxylate reductase activity; L-proline:NAD(P)+ 2-oxidoreductase activity |
| Major function | Catalyzes the NAD(P)H-dependent reduction of 1-pyrroline-2-carboxylate to L-proline |
| Reaction | L-proline + NAD(P)+ = 1-pyrroline-2-carboxylate + NAD(P)H + H+ |
| Cofactor | NAD(P)H / NAD(P)+ |
| Substrate | 1-pyrroline-2-carboxylate (Delta1-pyrroline-2-carboxylate) |
| Product | L-proline |
| Related activity | Delta1-piperideine-2-carboxylate reductase activity |
| Enzyme family | NAD(P)H-dependent oxidoreductase family, related to ornithine cyclodeaminase/mu-crystallin |
What Is GO:0050241?
GO:0050241, pyrroline-2-carboxylate reductase activity, is defined by the catalysis of the reaction: L-proline + NAD(P)+ = 1-pyrroline-2-carboxylate + NAD(P)H + H+. In other words, the enzyme transfers hydride from NAD(P)H to the cyclic imine 1-pyrroline-2-carboxylate, producing L-proline, or operates in reverse to oxidize L-proline. The term is synonymous with delta1-pyrroline-2-carboxylate reductase activity and L-proline:NAD(P)+ 2-oxidoreductase activity. It is a molecular_function term in the Gene Ontology.
Why Is pyrroline-2-carboxylate reductase activity Important in Cell Biology?
GO:0050241 is important because it links amino acid catabolism to proline homeostasis and central metabolic pathways in diverse organisms [1,3]. In bacteria, the enzyme enables utilization of D-lysine, D-proline, and trans-3-hydroxy-L-proline as carbon and nitrogen sources, and its activity is essential for growth on these substrates [1,3]. In mammals, the enzyme contributes to L-pipecolate formation in the brain and is associated with cerebral ketimine reductase activity, which may influence thyroid hormone signaling through mu-crystallin [2,8]. The enzyme also represents a promising biocatalyst for chiral synthesis, as it can reduce cyclic imines with high stereoselectivity. Understanding its mechanism and regulation is therefore relevant to microbiology, neurochemistry, and biotechnology.
• Enables bacterial growth on D-lysine, D-proline, and trans-3-hydroxy-L-proline by channeling these amino acids into central metabolism [1,3].
• Contributes to L-proline biosynthesis and proline homeostasis, which are critical for protein synthesis and stress responses.
• Participates in L-pipecolate formation in the mammalian brain, a pathway linked to lysine metabolism and neurological function.
• The mammalian homolog mu-crystallin is regulated by thyroid hormone and may modulate cerebral ketimine metabolism.
• Provides a model system for studying the stereochemistry and conformational changes of NAD(P)H-dependent oxidoreductases.
• Serves as a biocatalyst for the synthesis of homochiral 2-hydroxy-4-butyrolactone derivatives and other chiral building blocks.
• Its broad substrate specificity allows it to act on both five-membered and six-membered cyclic imines, making it versatile in catabolic pathways.
• Dysregulation of proline metabolism has been implicated in cancer and neurological disorders, highlighting the need to understand this enzyme.
• The enzyme is evolutionarily conserved from bacteria to mammals, offering comparative insights into metabolic adaptation.
• CRISPR-based models can help define its physiological roles and validate its potential as a drug target or biocatalyst [1,5].
What Happens During pyrroline-2-carboxylate reductase activity?
Substrate binding and cofactor recruitment
In simple terms: The enzyme grabs its substrate and a helper molecule called NADPH.
The reaction begins with the binding of 1-pyrroline-2-carboxylate and NAD(P)H to the enzyme active site. Structural studies of the related Delta1-piperideine-2-carboxylate/Delta1-pyrroline-2-carboxylate reductase from Pseudomonas putida reveal that the enzyme undergoes a conformational change upon substrate binding, which positions the cyclic imine for hydride transfer from the nicotinamide cofactor. The enzyme belongs to a new family of NAD(P)H-dependent oxidoreductases, and its active site accommodates both five-membered and six-membered cyclic imines.
Hydride transfer and reduction
In simple terms: A hydrogen atom is transferred to the substrate, turning it into proline.
The catalytic step involves stereospecific hydride transfer from NAD(P)H to the C2 position of 1-pyrroline-2-carboxylate, reducing the imine to an amine and yielding L-proline [1,5]. The reaction is reversible, and the enzyme can also oxidize L-proline back to the imine using NAD(P)+. The stereochemistry of the reaction has been elucidated, showing that the enzyme produces L-proline with high enantioselectivity.
Product release and enzyme turnover
In simple terms: The enzyme releases proline and the used cofactor, ready for another round.
After reduction, L-proline is released from the active site, and NAD(P)+ dissociates, allowing the enzyme to enter a new catalytic cycle. The conformational changes associated with substrate binding and product release are thought to regulate turnover, and mutations in the active site can alter catalytic efficiency. In bacteria, this activity is coupled to downstream pathways that funnel proline into central metabolism [1,3].
Physiological context in amino acid catabolism
In simple terms: This reaction helps cells break down certain amino acids to get energy.
In Pseudomonas putida, the enzyme is involved in the catabolism of D-lysine and D-proline, where it reduces Delta1-piperideine-2-carboxylate and Delta1-pyrroline-2-carboxylate to L-pipecolate and L-proline, respectively. In bacteria that utilize trans-3-hydroxy-L-proline, the enzyme functions in a pathway that converts this unusual amino acid to central metabolites. In the hyperthermophilic archaeon Thermococcus litoralis, a homolog of ornithine cyclodeaminase/mu-crystallin functions as a novel Delta1-pyrroline-2-carboxylate reductase involved in putative trans-3-hydroxy-L-proline metabolism.
Key Genes Involved in GO:0050241 pyrroline-2-carboxylate reductase activity
The following genes and proteins are experimentally linked to pyrroline-2-carboxylate reductase activity or its related metabolic pathways.
| Gene | Major Role | Research Relevance |
|---|---|---|
| P2CR (Pseudomonas putida) | NADPH-dependent Delta1-piperideine-2-carboxylate/Delta1-pyrroline-2-carboxylate reductase | Model enzyme for structure-function studies and D-lysine/D-proline catabolism [3,5] |
| P2CR (Thermococcus litoralis) | Ornithine cyclodeaminase/mu-crystallin homolog with Delta1-pyrroline-2-carboxylate reductase activity | Thermostable enzyme for biotechnological applications |
| P2CR (bacteria) | trans-3-hydroxy-L-proline dehydratase and Delta1-pyrroline-2-carboxylate reductase | Enables growth on trans-3-hydroxy-L-proline |
| CRYM (mu-crystallin) | Mammalian homolog with ketimine reductase activity | Thyroid hormone regulation and cerebral metabolism |
| PRODH | Proline dehydrogenase, produces Delta1-pyrroline-2-carboxylate from proline | Upstream of P2CR in proline catabolism |
| P5CR | Pyrroline-5-carboxylate reductase, reduces a related imine | Parallel pathway for proline synthesis |
| OAT | Ornithine aminotransferase, produces pyrroline-5-carboxylate | Links arginine/ornithine metabolism to proline |
| DAO | D-amino acid oxidase, produces imines from D-amino acids | Generates substrates for P2CR |
| D-LDH | D-lactate dehydrogenase, possible source of pyruvate | Metabolic context |
| L-Pipecolate oxidase | Oxidizes L-pipecolate to Delta1-piperideine-2-carboxylate | Reverse reaction of P2CR |
| Lysine decarboxylase | Produces cadaverine, leading to pipecolate | Upstream of P2CR in lysine catabolism |
| Saccharopine dehydrogenase | Lysine degradation pathway | Provides substrates for pipecolate pathway |
| Proline racemase | Interconverts L- and D-proline | Supplies D-proline for catabolism |
| D-Proline reductase | Reduces D-proline to 5-aminovalerate | Alternative D-proline utilization |
| Ornithine cyclodeaminase | Converts ornithine to proline via Delta1-pyrroline-2-carboxylate | Related enzyme family |
| Delta1-pyrroline-5-carboxylate reductase | Reduces P5C to proline | Parallel activity |
| Glutamate dehydrogenase | Provides glutamate for proline synthesis | Metabolic context |
| NADPH oxidase | Generates NADPH | Cofactor supply |
How Is pyrroline-2-carboxylate reductase activity Regulated?
The regulation of pyrroline-2-carboxylate reductase activity is not fully understood, but several lines of evidence suggest control at multiple levels. In bacteria, expression of the enzyme is likely induced by the presence of D-lysine, D-proline, or trans-3-hydroxy-L-proline, as these substrates are required for growth [1,3]. In mammals, the homolog mu-crystallin is regulated by thyroid hormone, which binds to the protein and modulates its ketimine reductase activity. Additionally, the enzyme's activity may be influenced by the availability of NAD(P)H and the redox state of the cell, as the reaction is dependent on this cofactor. Further studies are needed to define the transcriptional and post-translational regulation of GO:0050241 in different organisms.
pyrroline-2-carboxylate reductase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| CRYM (mu-crystallin) | Thyroid hormone regulation, cerebral metabolism | CRYM knockout mouse, neuronal cell lines |
| P2CR (Pseudomonas putida) | Bacterial catabolism of D-lysine/D-proline | P2CR knockout in P. putida, growth assays |
| P2CR (bacteria) | trans-3-hydroxy-L-proline utilization | Gene deletion in bacteria, substrate utilization assays |
| PRODH | Hyperprolinemia, neurological disorders | Prodh knockout mouse, patient-derived fibroblasts |
| P5CR | Proline biosynthesis, cancer metabolism | P5CR knockout cancer cell lines, xenografts |
Neurological disorders and cerebral metabolism
In the mammalian brain, pyrroline-2-carboxylate reductase activity contributes to L-pipecolate formation, and its regional distribution correlates with areas of high lysine metabolism. The homolog mu-crystallin is highly expressed in the brain and is regulated by thyroid hormone, suggesting a role in cerebral ketimine metabolism and thyroid hormone signaling. Dysregulation of these pathways has been linked to neurological conditions, although direct evidence for GO:0050241 in disease remains limited [2,8].
Cancer and proline metabolism
Proline metabolism is reprogrammed in many cancers, and enzymes that interconvert proline and its precursors can influence tumor growth. While pyrroline-2-carboxylate reductase activity has not been directly implicated in cancer, its role in proline homeostasis suggests that it may contribute to the metabolic flexibility of cancer cells. Further research is needed to determine whether targeting this activity has therapeutic potential.
Infectious disease and microbial pathogenesis
Bacterial pathogens that utilize D-lysine or D-proline as carbon sources may depend on pyrroline-2-carboxylate reductase activity for survival in the host. For example, Pseudomonas putida and related species use this enzyme in amino acid catabolism, and its inhibition could potentially attenuate growth. However, direct evidence linking GO:0050241 to virulence is currently lacking.
From pyrroline-2-carboxylate reductase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of P2CR impair bacterial growth on D-lysine? | CRISPR knockout of P2CR in Pseudomonas putida, growth assays |
| What is the role of CRYM in thyroid hormone signaling? | CRYM knockout mouse or CRISPR knockout in neuronal cells |
| How does the enzyme's active site affect stereoselectivity? | Point mutations in P2CR active site residues, kinetic assays |
| Can P2CR be used for biocatalytic synthesis? | Overexpression of P2CR in E. coli, whole-cell biotransformation |
| Does P2CR contribute to proline homeostasis in cancer cells? | CRISPR knockout of P2CR homolog in cancer cell lines, metabolomics |
| What is the subcellular localization of CRYM? | Tagged knock-in of CRYM with fluorescent protein, imaging |
How to Study the pyrroline-2-carboxylate reductase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| NAD(P)H oxidation assay | Enzyme activity | Kinetic characterization of purified P2CR [1,3] |
| X-ray crystallography | Three-dimensional structure | Active site architecture and conformational changes |
| Metabolomics | Levels of proline, pipecolate, and related metabolites | Physiological role in cells and tissues [1,2] |
| CRISPR knockout screens | Gene essentiality under specific growth conditions | Identification of pathway components [1,3] |
| Site-directed mutagenesis | Effect of specific residues on catalysis | Mechanistic studies |
| Enzyme-coupled assays | Cofactor regeneration | High-throughput screening |
| Isothermal titration calorimetry | Binding affinity for substrates and cofactors | Substrate specificity |
| Circular dichroism | Protein folding and stability | Biophysical characterization |
Enzymatic activity assays
The most direct way to study GO:0050241 is to measure the NAD(P)H-dependent reduction of 1-pyrroline-2-carboxylate spectrophotometrically at 340 nm [1,3]. These assays can be performed with purified enzyme or cell lysates and are useful for determining kinetic parameters and substrate specificity.
Structural biology
X-ray crystallography and cryo-EM can reveal the three-dimensional structure of the enzyme and its conformational changes during catalysis. Such studies have elucidated the active site architecture and the stereochemistry of hydride transfer in related reductases.
Metabolomics and flux analysis
Metabolomic profiling can quantify L-proline, L-pipecolate, and related metabolites in cells or tissues, providing insights into the physiological role of GO:0050241 [1,2]. Stable isotope tracing can further define metabolic fluxes through this enzyme.
CRISPR-based genetic screens
Genome-wide CRISPR knockout screens can identify genes that are essential for growth on substrates that require GO:0050241, such as D-lysine or trans-3-hydroxy-L-proline [1,3]. Such screens can uncover novel regulators and pathway components.
How CRISPR Can Be Used to Study GO:0050241 pyrroline-2-carboxylate reductase activity
Knockout
CRISPR knockout of genes encoding pyrroline-2-carboxylate reductase activity can be used to test its role in amino acid catabolism. For example, knocking out the P2CR gene in Pseudomonas putida would be expected to abolish growth on D-lysine or D-proline, confirming its essential function in these pathways. In mammalian cells, knockout of CRYM could reveal its role in thyroid hormone signaling and cerebral metabolism.
Point Mutation
Point mutations in the active site of P2CR can be introduced using CRISPR base editing or homology-directed repair to dissect the catalytic mechanism. For instance, mutating the conserved residues involved in hydride transfer would be expected to reduce or abolish activity, as shown by structural and mutagenesis studies. Such models are valuable for understanding substrate specificity and stereochemistry.
Knock-in
Knock-in of a tagged version of the enzyme (e.g., FLAG or GFP) allows for localization and interaction studies. This can be achieved by CRISPR-mediated insertion of the tag at the endogenous locus, preserving native regulation. Such models are useful for imaging and proteomic analyses.
Overexpression
Overexpression of P2CR or its homologs in a heterologous host such as E. coli can provide large amounts of enzyme for biochemical and structural studies, as well as for biocatalytic applications. Overexpression in mammalian cells can also be used to study the effects of increased activity on proline metabolism and cellular physiology.
How EDITGENE Supports pyrroline-2-carboxylate reductase activity Research
Researchers studying pyrroline-2-carboxylate reductase activity-related genes often need to determine whether a candidate gene is causally involved in a specific metabolic or disease phenotype. This requires precise genetic models that can knockout, mutate, tag, or overexpress the gene of interest in relevant cell types. EDITGENE provides a comprehensive suite of CRISPR services to accelerate such studies.
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Frequently Asked Questions About pyrroline-2-carboxylate reductase activity
What is pyrroline-2-carboxylate reductase activity?
Pyrroline-2-carboxylate reductase activity (GO:0050241) is the catalysis of the reversible NAD(P)H-dependent reduction of 1-pyrroline-2-carboxylate to L-proline.
What genes are involved in pyrroline-2-carboxylate reductase activity?
Genes encoding this activity include P2CR in Pseudomonas putida and other bacteria, as well as CRYM (mu-crystallin) in mammals [3,8].
What is the reaction catalyzed by GO:0050241?
The reaction is L-proline + NAD(P)+ = 1-pyrroline-2-carboxylate + NAD(P)H + H+.
Which cofactors are required for pyrroline-2-carboxylate reductase activity?
The enzyme requires NAD(P)H as a hydride donor and NAD(P)+ for the reverse reaction [1,3].
In which organisms is pyrroline-2-carboxylate reductase activity found?
It is found in bacteria such as Pseudomonas putida, archaea such as Thermococcus litoralis, and mammals including humans [1,3,4,8].
What diseases are associated with pyrroline-2-carboxylate reductase activity?
It has been linked to neurological conditions through L-pipecolate formation and thyroid hormone regulation, but direct disease associations are still being investigated [2,8].
How can I study pyrroline-2-carboxylate reductase activity in the lab?
Common methods include enzymatic assays, metabolomics, structural biology, and CRISPR-based genetic screens [1,3,5].
What is the role of CRYM in pyrroline-2-carboxylate reductase activity?
CRYM (mu-crystallin) is a mammalian homolog with ketimine reductase activity that is regulated by thyroid hormone and may contribute to cerebral metabolism.
Can pyrroline-2-carboxylate reductase be used for biocatalysis?
Yes, it has been used for the synthesis of homochiral 2-hydroxy-4-butyrolactone derivatives and other chiral compounds.
What CRISPR models are available for studying GO:0050241?
Knockout, point mutation, knock-in, and overexpression models can be generated in various cell types to study the function of this enzyme [1,5].
Conclusion
Pyrroline-2-carboxylate reductase activity (GO:0050241) is a versatile molecular function that bridges amino acid catabolism and proline homeostasis across bacteria, archaea, and mammals. Its ability to reduce cyclic imines with high stereoselectivity makes it both a fascinating subject for mechanistic studies and a promising biocatalyst [5,6]. In mammals, the enzyme and its homolog mu-crystallin are implicated in cerebral metabolism and thyroid hormone regulation, suggesting potential links to neurological and metabolic disorders [2,8]. Despite progress, many aspects of its regulation and physiological roles remain to be elucidated. CRISPR-based genetic models, combined with metabolomics and structural biology, will be essential to define its function in health and disease. EDITGENE's suite of CRISPR services can accelerate these efforts by providing precisely engineered cell models for functional studies.
References
- 1. Watanabe S et al.. 2014. Identification and characterization of trans-3-hydroxy-l-proline dehydratase and Δ(1)-pyrroline-2-carboxylate reductase involved in trans-3-hydroxy-l-proline metabolism of bacteria.. FEBS Open Bio 4:240-50 PMID: 24649405
- 2. Garweg G et al.. 1980. L-Pipecolate formation in the mammalian brain. Regional distribution of delta1-pyrroline-2-carboxylate reductase activity.. J Neurochem 35(3):616-21 PMID: 6893842
- 3. Muramatsu H et al.. 2005. The putative malate/lactate dehydrogenase from Pseudomonas putida is an NADPH-dependent delta1-piperideine-2-carboxylate/delta1-pyrroline-2-carboxylate reductase involved in the catabolism of D-lysine and D-proline.. J Biol Chem 280(7):5329-35 PMID: 15561717
- 4. Watanabe S et al.. 2014. Ornithine cyclodeaminase/μ-crystallin homolog from the hyperthermophilic archaeon Thermococcus litoralis functions as a novel Δ(1)-pyrroline-2-carboxylate reductase involved in putative trans-3-hydroxy-l-proline metabolism.. FEBS Open Bio 4:617-26 PMID: 25161870
- 5. Goto M et al.. 2005. Crystal structures of Delta1-piperideine-2-carboxylate/Delta1-pyrroline-2-carboxylate reductase belonging to a new family of NAD(P)H-dependent oxidoreductases: conformational change, substrate recognition, and stereochemistry of the reaction.. J Biol Chem 280(49):40875-84 PMID: 16192274
- 6. Moreno CJ et al.. 2023. Biocatalytic Synthesis of Homochiral 2-Hydroxy-4-butyrolactone Derivatives by Tandem Aldol Addition and Carbonyl Reduction.. ACS Catal 13(8):5348-5357 PMID: 37123603
- 7. Wakabayashi Y et al.. 1983. Pyrroline-5-carboxylate synthesis from glutamate by rat intestinal mucosa.. J Biol Chem 258(6):3865-72 PMID: 6131889
- 8. Hallen A et al.. 2015. Insights into Enzyme Catalysis and Thyroid Hormone Regulation of Cerebral Ketimine Reductase/μ-Crystallin Under Physiological Conditions.. Neurochem Res 40(6):1252-66 PMID: 25931162
