GO:0000248 C-5 sterol desaturase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0000248 C-5 sterol desaturase activity catalyzes the introduction of a C-5 double bond into sterol precursors, converting 5,7,24(28)-ergostatrienol to 5,7,22,24(28)-ergostatetraenol using O2 and NADPH.
• This enzymatic step is essential for ergosterol biosynthesis in fungi and for the production of Δ5,7 sterols in protozoa and oomycetes.
• Loss of C-5 sterol desaturase activity, often through ERG3 mutations, alters membrane sterol composition and can confer resistance to azole antifungals in Candida species.
• The enzyme is a cytochrome b5-dependent desaturase located in the endoplasmic reticulum, and its activity is influenced by host immune status and species-specific factors.
• Research on this activity spans antifungal drug discovery, sterol auxotrophy in Phytophthora capsici, and complementation studies in Saccharomyces cerevisiae.
• CRISPR-based knockout, point mutation, and knock-in models enable precise dissection of C-5 sterol desaturase function in pathogenic and non-pathogenic organisms.
Description
C-5 sterol desaturase activity (GO:0000248) is a molecular function that introduces a double bond at the C-5 position of sterol precursors, a critical modification in the biosynthesis of ergosterol and related sterols. This activity is defined by the reaction: 5,7,24(28)-ergostatrienol + O2 + NADPH = 5,7,22,24(28)-ergostatetraenol + 2 H2O + NADP+. The enzyme responsible, often encoded by ERG3 in fungi, is a cytochrome b5-dependent desaturase localized to the endoplasmic reticulum. Researchers study this activity because it directly impacts membrane integrity, antifungal susceptibility, and the virulence of fungal pathogens. In Candida albicans, titrating C-5 sterol desaturase activity reveals a complex relationship with virulence and azole resistance that depends on host immune status. Similarly, species-specific differences in enzyme function influence the outcome of azole exposure in Candida species. Beyond fungi, the enzyme is found in protozoa like Tetrahymena thermophila and oomycetes such as Phytophthora capsici, where it supports sterol auxotrophy and developmental processes. Understanding GO:0000248 is therefore central to microbiology, pharmacology, and cell biology, offering insights into membrane biology and drug resistance mechanisms.
C-5 sterol desaturase activity At A Glance
| GO ID | GO:0000248 |
|---|---|
| GO term | C-5 sterol desaturase activity |
| Ontology | molecular_function |
| Synonym | sterol-C5-desaturase activity |
| Major function | Catalyzes the introduction of a C-5 double bond into sterol precursors during ergosterol biosynthesis |
| Reaction | 5,7,24(28)-ergostatrienol + O2 + NADPH = 5,7,22,24(28)-ergostatetraenol + 2 H2O + NADP+ |
| Cofactors | O2, NADPH, cytochrome b5 |
| Localization | Endoplasmic reticulum |
| Representative genes | ERG3 (Candida albicans, Saccharomyces cerevisiae), DES5A (Tetrahymena thermophila), PcErg3 (Phytophthora capsici) |
What Is GO:0000248?
C-5 sterol desaturase activity is the catalysis of the reaction: 5,7,24(28)-ergostatrienol + O2 + NADPH = 5,7,22,24(28)-ergostatetraenol + 2 H2O + NADP+. This reaction introduces a double bond at the C-5 position of the sterol B-ring, a step required for the synthesis of ergosterol in fungi and for the formation of Δ5,7 sterols in other organisms. The enzyme uses molecular oxygen and NADPH as cofactors and is dependent on cytochrome b5 for electron transfer.
Why Is C-5 sterol desaturase activity Important in Cell Biology?
C-5 sterol desaturase activity is a pivotal step in sterol biosynthesis, influencing membrane fluidity, permeability, and the efficacy of antifungal drugs. In pathogenic fungi, alterations in this activity can lead to azole resistance, a major clinical challenge. The enzyme also plays a role in the virulence of Candida albicans, with its impact modulated by host immune status. In sterol auxotrophs like Phytophthora capsici, it is essential for growth and development, making it a potential target for oomycete control. Furthermore, the enzyme is a model for studying cytochrome b5-dependent desaturation and sterol trafficking in eukaryotes. Its conservation across fungi, protozoa, and oomycetes underscores its broad biological significance.
• Critical for ergosterol biosynthesis and membrane integrity in fungi.
• Mutations in ERG3 leading to loss of C-5 sterol desaturase activity are associated with azole resistance in Candida species.
• Modulates virulence of Candida albicans in a host immune status-dependent manner.
• Species-specific differences in enzyme function affect antifungal susceptibility.
• Essential for sterol auxotrophy and pathogenicity in Phytophthora capsici.
• Provides a model for cytochrome b5-dependent desaturation mechanisms.
• Potential target for antifungal drug development.
• Involved in post-squalene sterol pathway regulation in yeast.
• Complementation studies in Saccharomyces cerevisiae highlight functional conservation.
• Relevant to understanding sterol-related disorders and membrane biology.
What Happens During C-5 sterol desaturase activity?
Substrate Binding and Activation
In simple terms: The enzyme grabs a sterol molecule and prepares it for modification.
The C-5 sterol desaturase binds its substrate, 5,7,24(28)-ergostatrienol, within the endoplasmic reticulum membrane. The enzyme is a cytochrome b5-dependent desaturase, requiring electron transfer from NADPH via cytochrome b5 to activate molecular oxygen. This activation leads to the formation of a reactive oxygen species that abstracts a hydrogen atom from the sterol C-5 position.
Catalytic Desaturation
In simple terms: A double bond is created at the C-5 position of the sterol ring.
Following hydrogen abstraction, the enzyme introduces a double bond between C-5 and C-6, converting 5,7,24(28)-ergostatrienol to 5,7,22,24(28)-ergostatetraenol. This desaturation step is essential for the subsequent formation of ergosterol. The reaction consumes O2 and NADPH and produces water and NADP+.
Product Release and Pathway Flux
In simple terms: The modified sterol is released to continue down the biosynthesis pathway.
After catalysis, the product 5,7,22,24(28)-ergostatetraenol is released into the sterol biosynthetic pathway, where it undergoes further modifications to yield ergosterol. The activity of C-5 sterol desaturase influences the flux of post-squalene sterols, and its loss leads to the accumulation of alternative sterols that can alter membrane properties and drug susceptibility.
Regulation of Enzyme Levels
In simple terms: The amount of enzyme in the cell is controlled by genetic and environmental factors.
Expression of the ERG3 gene, encoding C-5 sterol desaturase, is regulated positively and negatively in the post-squalene portion of the yeast ergosterol pathway. In Candida albicans, titration of enzyme activity reveals a dose-dependent relationship with virulence and antifungal resistance, suggesting tight regulation is important for adaptation. Species-specific differences in regulation further modulate the outcome of azole exposure.
Key Genes Involved in GO:0000248 C-5 sterol desaturase activity
The following genes and proteins are directly associated with C-5 sterol desaturase activity across various organisms.
| Gene | Major Role | Research Relevance |
|---|---|---|
| ERG3 (Candida albicans) | Encodes C-5 sterol desaturase | Mutations linked to azole resistance and virulence |
| ERG3 (Saccharomyces cerevisiae) | Encodes C-5 sterol desaturase | Model for sterol biosynthesis regulation |
| ERG3 (Candida parapsilosis) | Encodes C-5 sterol desaturase | Loss confers resistance to azoles and echinocandins |
| DES5A (Tetrahymena thermophila) | Cytochrome b5-dependent C-5(6) sterol desaturase | Complements ergosterol mutants in yeast |
| PcErg3 (Phytophthora capsici) | C-5 sterol desaturase | Essential for sterol auxotrophy and development |
| ERG3 (Candida glabrata) | C-5 sterol desaturase | Species-specific azole response |
| ERG3 (Candida auris) | C-5 sterol desaturase | Potential role in antifungal resistance |
| ERG3 (Aspergillus fumigatus) | C-5 sterol desaturase | Azole resistance mechanisms |
| ERG3 (Cryptococcus neoformans) | C-5 sterol desaturase | Sterol biosynthesis and virulence |
| ERG3 (Schizosaccharomyces pombe) | C-5 sterol desaturase | Model for sterol pathway |
| ERG3 (Yarrowia lipolytica) | C-5 sterol desaturase | Lipid production and sterol engineering |
| ERG3 (Candida tropicalis) | C-5 sterol desaturase | Azole susceptibility |
| ERG3 (Candida dubliniensis) | C-5 sterol desaturase | Sterol composition and resistance |
| ERG3 (Candida lusitaniae) | C-5 sterol desaturase | Antifungal response |
| ERG3 (Candida guilliermondii) | C-5 sterol desaturase | Sterol pathway diversity |
| ERG3 (Candida metapsilosis) | C-5 sterol desaturase | Comparative genomics |
| ERG3 (Candida orthopsilosis) | C-5 sterol desaturase | Azole resistance |
How Is C-5 sterol desaturase activity Regulated?
C-5 sterol desaturase activity is regulated at multiple levels. In Saccharomyces cerevisiae, the ERG3 gene is subject to positive and negative regulation in the post-squalene portion of the ergosterol pathway, responding to sterol intermediates and cellular needs. In Candida albicans, titration of enzyme activity reveals a dose-dependent effect on virulence and antifungal susceptibility, indicating that fine-tuning of expression is critical for host adaptation. Host immune status further modulates the impact of enzyme loss, suggesting that environmental cues influence regulation. Species-specific differences in regulation of C-5 sterol desaturase function also affect the outcome of azole exposure, highlighting evolutionary divergence in regulatory networks.
C-5 sterol desaturase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| ERG3 (Candida albicans) | Candidiasis, azole resistance | KO, point mutation, and titrated expression in C. albicans |
| ERG3 (Candida parapsilosis) | Antifungal resistance | Clinical isolate with ERG3 loss-of-function |
| PcErg3 (Phytophthora capsici) | Oomycete plant disease | Knockout and complementation in P. capsici |
| DES5A (Tetrahymena thermophila) | Sterol biosynthesis model | Knockout and heterologous expression in S. cerevisiae |
| ERG3 (Saccharomyces cerevisiae) | Ergosterol pathway regulation | Deletion and promoter analysis |
Candidiasis and Antifungal Resistance
Candida albicans is a major human fungal pathogen, and loss of C-5 sterol desaturase activity through ERG3 mutations is associated with azole resistance, a significant clinical problem. The relationship between enzyme activity and virulence is dependent on host immune status, with titrated activity influencing disease outcomes. In Candida parapsilosis, loss of C-5 sterol desaturase activity results in increased resistance to both azole and echinocandin antifungals in clinical isolates. These findings underscore the importance of this enzyme in antifungal drug efficacy and fungal pathogenesis.
Oomycete Pathogenesis
Phytophthora capsici is a sterol auxotrophic oomycete pathogen that causes devastating crop diseases. The C-5 sterol desaturase PcErg3 is essential for sterol biosynthesis and normal development, and its functional analysis provides insights into oomycete sterol metabolism and potential control strategies.
Sterol Biosynthesis Disorders
While C-5 sterol desaturase is primarily studied in microbes, its mechanism is relevant to understanding sterol biosynthesis in higher eukaryotes. The enzyme from Tetrahymena thermophila, DES5A, complements ergosterol biosynthesis mutants in Saccharomyces cerevisiae, demonstrating functional conservation and providing a model for studying cytochrome b5-dependent desaturation in sterol-related disorders.
From C-5 sterol desaturase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the effect of complete loss of C-5 sterol desaturase on virulence? | CRISPR knockout of ERG3 in Candida albicans |
| How do point mutations in ERG3 affect enzyme activity and azole resistance? | CRISPR point mutation knock-in in Candida species |
| Can a heterologous C-5 sterol desaturase complement yeast mutants? | Knock-in of DES5A into Saccharomyces cerevisiae erg3 mutants |
| What is the impact of titrated enzyme expression on host immune interaction? | Overexpression and inducible knockdown in Candida albicans |
| How does PcErg3 contribute to sterol auxotrophy in oomycetes? | CRISPR knockout in Phytophthora capsici |
| What are the regulatory elements controlling ERG3 expression? | Promoter-reporter knock-in in Saccharomyces cerevisiae |
How to Study the C-5 sterol desaturase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| GC-MS sterol profiling | Sterol intermediate and end-product levels | Quantifying C-5 desaturase activity in mutants |
| LC-MS | Sterol composition | Confirming substrate and product identity |
| Broth microdilution MIC | Antifungal susceptibility | Linking enzyme loss to azole resistance |
| qRT-PCR | ERG3 mRNA levels | Studying transcriptional regulation |
| Promoter-reporter assay | Transcriptional activity | Mapping regulatory elements |
| CRISPR knockout | Gene function | Creating loss-of-function models |
| Complementation assay | Functional conservation | Testing heterologous genes in yeast |
| Site-directed mutagenesis | Enzyme activity of variants | Structure-function analysis |
Genetic Knockout and Complementation
Targeted gene deletion of ERG3 or its homologs is a primary method to study C-5 sterol desaturase activity. In Candida albicans, knockout mutants display altered sterol profiles and antifungal susceptibility. Complementation of Saccharomyces cerevisiae erg3 mutants with DES5A from Tetrahymena thermophila confirms functional conservation and allows structure-function studies. In Phytophthora capsici, knockout of PcErg3 reveals its role in sterol auxotrophy and development.
Sterol Profiling by Mass Spectrometry
Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) are used to quantify sterol intermediates and end products, directly measuring the impact of C-5 sterol desaturase activity on the sterol profile. These methods reveal the accumulation of 5,7,24(28)-ergostatrienol and depletion of 5,7,22,24(28)-ergostatetraenol in mutants.
Antifungal Susceptibility Testing
Broth microdilution assays determine minimal inhibitory concentrations (MICs) of azoles and echinocandins in strains with altered C-5 sterol desaturase activity. These tests are critical for linking enzyme function to drug resistance phenotypes and for evaluating trailing growth effects.
Gene Expression Analysis
Quantitative RT-PCR and promoter-reporter assays are used to study the regulation of ERG3 expression under different conditions, including azole exposure and host immune factors. These methods help elucidate the transcriptional control of C-5 sterol desaturase activity.
How CRISPR Can Be Used to Study GO:0000248 C-5 sterol desaturase activity
Knockout
CRISPR-Cas9 knockout of ERG3 or homologous genes is used to completely abolish C-5 sterol desaturase activity. In Candida albicans, ERG3 knockout mutants show altered sterol profiles and reduced virulence in a host immune status-dependent manner. In Phytophthora capsici, knockout of PcErg3 confirms its essential role in sterol auxotrophy. These models are valuable for studying the consequences of enzyme loss on membrane function and drug resistance.
Point Mutation
CRISPR-mediated point mutations can introduce specific amino acid substitutions in C-5 sterol desaturase to dissect catalytic residues and regulatory sites. Such models help determine how missense mutations in ERG3 affect enzyme activity and azole resistance, as observed in clinical isolates of Candida species. Point mutations also allow fine-tuning of activity to study dose-dependent effects on virulence.
Knock-in
Knock-in of tagged or heterologous C-5 sterol desaturase genes enables localization, interaction, and complementation studies. For example, knock-in of DES5A from Tetrahymena thermophila into Saccharomyces cerevisiae erg3 mutants restores ergosterol biosynthesis, demonstrating functional conservation. Tagged knock-in with fluorescent proteins facilitates live-cell imaging of enzyme localization in the endoplasmic reticulum.
Overexpression
CRISPR activation or promoter replacement can drive overexpression of C-5 sterol desaturase to study the effects of increased enzyme levels on sterol flux and antifungal susceptibility. In Candida albicans, titrated overexpression reveals a complex relationship between enzyme activity, virulence, and host immune status. Overexpression models are also useful for biochemical purification and kinetic studies.
How EDITGENE Supports C-5 sterol desaturase activity Research
Researchers studying C-5 sterol desaturase activity-related genes often need to determine whether a candidate gene is causally involved in sterol biosynthesis, antifungal resistance, or virulence. EDITGENE provides comprehensive CRISPR-based services to create precise cellular models for such investigations.
Contact EDITGENE today to design your custom CRISPR model for C-5 sterol desaturase activity research.
Frequently Asked Questions About C-5 sterol desaturase activity
What is C-5 sterol desaturase activity?
C-5 sterol desaturase activity (GO:0000248) is a molecular function that catalyzes the introduction of a double bond at the C-5 position of sterol precursors, converting 5,7,24(28)-ergostatrienol to 5,7,22,24(28)-ergostatetraenol using O2 and NADPH.
What genes are involved in C-5 sterol desaturase activity?
The primary gene is ERG3 in fungi such as Candida albicans and Saccharomyces cerevisiae. Homologs include DES5A in Tetrahymena thermophila and PcErg3 in Phytophthora capsici.
How does loss of C-5 sterol desaturase activity affect antifungal resistance?
Loss of activity, often through ERG3 mutations, alters sterol composition and can confer resistance to azole and echinocandin antifungals in Candida species.
Is C-5 sterol desaturase activity important for virulence?
Yes, in Candida albicans, titrated activity influences virulence in a host immune status-dependent manner. In Phytophthora capsici, it is essential for sterol auxotrophy and development.
What is the reaction catalyzed by C-5 sterol desaturase?
The reaction is: 5,7,24(28)-ergostatrienol + O2 + NADPH = 5,7,22,24(28)-ergostatetraenol + 2 H2O + NADP+.
Where is C-5 sterol desaturase located in the cell?
The enzyme is localized to the endoplasmic reticulum membrane.
What cofactors are required for C-5 sterol desaturase activity?
The enzyme requires molecular oxygen (O2), NADPH, and cytochrome b5 for electron transfer.
How is C-5 sterol desaturase activity regulated?
In Saccharomyces cerevisiae, ERG3 is regulated positively and negatively in the post-squalene pathway. In Candida albicans, activity is titrated and influenced by host immune status.
Can C-5 sterol desaturase from other organisms complement yeast mutants?
Yes, DES5A from Tetrahymena thermophila complements ergosterol biosynthesis mutants in Saccharomyces cerevisiae.
What methods are used to study C-5 sterol desaturase activity?
Common methods include GC-MS sterol profiling, antifungal susceptibility testing, qRT-PCR, CRISPR knockout, and complementation assays.
Conclusion
C-5 sterol desaturase activity (GO:0000248) is a critical enzymatic step in sterol biosynthesis, with profound implications for fungal virulence, antifungal resistance, and membrane biology. Its study across diverse organisms, from Candida albicans to Phytophthora capsici, has revealed species-specific differences and regulatory complexity. Advances in CRISPR-based models now enable precise manipulation of this activity, facilitating drug discovery and fundamental research. Continued investigation of C-5 sterol desaturase will illuminate sterol-related pathways and inform therapeutic strategies against fungal and oomycete pathogens.
References
- 1. Regan J et al.. 2022. Titration of C-5 Sterol Desaturase Activity Reveals Its Relationship to Candida albicans Virulence and Antifungal Susceptibility Is Dependent upon Host Immune Status.. mBio 13(2):e0011522 PMID: 35380453
- 2. Luna-Tapia A et al.. 2021. Species-Specific Differences in C-5 Sterol Desaturase Function Influence the Outcome of Azole Antifungal Exposure.. Antimicrob Agents Chemother 65(12):e0104421 PMID: 34516249
- 3. Wang W et al.. 2022. Functional Analysis of the C-5 Sterol Desaturase PcErg3 in the Sterol Auxotrophic Oomycete Pathogen Phytophthora capsici.. Front Microbiol 13:811132 PMID: 35651492
- 4. Luna-Tapia A et al.. 2019. Loss of C-5 Sterol Desaturase Activity in Candida albicans: Azole Resistance or Merely Trailing Growth?. Antimicrob Agents Chemother 63(1) PMID: 30323044
- 5. Rybak JM et al.. 2017. Loss of C-5 Sterol Desaturase Activity Results in Increased Resistance to Azole and Echinocandin Antifungals in a Clinical Isolate of Candida parapsilosis.. Antimicrob Agents Chemother 61(9) PMID: 28630186
- 6. Poklepovich TJ et al.. 2012. The cytochrome b5 dependent C-5(6) sterol desaturase DES5A from the endoplasmic reticulum of Tetrahymena thermophila complements ergosterol biosynthesis mutants in Saccharomyces cerevisiae.. Steroids 77(13):1313-20 PMID: 22982564
- 7. Arthington-Skaggs BA et al.. 1996. Positive and negative regulation of a sterol biosynthetic gene (ERG3) in the post-squalene portion of the yeast ergosterol pathway.. FEBS Lett 392(2):161-5 PMID: 8772195
- 8. Nusblat AD et al.. 2009. C-5(6) sterol desaturase from tetrahymena thermophila: Gene identification and knockout, sequence analysis, and comparison to other C-5(6) sterol desaturases.. Eukaryot Cell 8(8):1287-97 PMID: 19525418
