GO:0003919 FMN adenylyltransferase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0003919 (FMN adenylyltransferase activity) catalyzes the reaction FMN + ATP + H+ = FAD + diphosphate, the final step in FAD cofactor biosynthesis.
• The enzyme is widely known as FAD synthetase (FADS) and exists as bifunctional proteins in prokaryotes (riboflavin kinase/FMN adenylyltransferase) and as distinct or fused enzymes in eukaryotes and plants.
• Structural and mutational studies have identified key residues (e.g., F26 in Staphylococcus aureus FADS, an arginine in the adenylyltransferase module) that control substrate binding and catalysis.
• In humans, FAD synthase (FLAD1) is a bifunctional enzyme whose dysfunction is linked to rare metabolic disorders and potential drug targets in pathogens.
• CRISPR/Cas9 site-directed mutagenesis of FAD synthetase genes can enhance riboflavin/FAD production in industrial strains.
• Research on GO:0003919 spans enzymology, structural biology, metabolic engineering, and infectious disease, making it a versatile target for gene-editing studies.
Description
FMN adenylyltransferase activity (GO:0003919) is the molecular function that catalyzes the transfer of an adenylyl group from ATP to flavin mononucleotide (FMN), yielding flavin adenine dinucleotide (FAD) and diphosphate. This reaction represents the terminal step in the biosynthesis of FAD, an essential redox cofactor required by hundreds of flavoenzymes involved in energy metabolism, oxidative stress responses, and DNA repair. Because FAD is indispensable for cellular respiration and numerous biosynthetic pathways, the enzyme responsible for its production has attracted attention across microbiology, plant biology, and human medicine. Researchers studying this activity seek to understand its catalytic mechanism, its structural determinants, and how its modulation affects cellular physiology and disease. The enzyme is known by many synonyms, including FAD synthetase, FAD pyrophosphorylase, and ATP:FMN adenylyltransferase, reflecting its historical characterization in different organisms. In prokaryotes, the activity often resides within a bifunctional enzyme that also carries riboflavin kinase activity, while in eukaryotes and plants it can be a separate domain or a fused protein with additional modules. This architectural diversity makes GO:0003919 a rich subject for comparative enzymology and for CRISPR-based functional studies.
FMN adenylyltransferase activity At A Glance
| GO ID | GO:0003919 |
|---|---|
| GO term | FMN adenylyltransferase activity |
| Ontology | molecular_function |
| Synonym | FAD synthetase activity; FAD pyrophosphorylase activity; ATP:FMN adenylyltransferase activity; riboflavin mononucleotide adenylyltransferase activity |
| Major function | Catalyzes the conversion of FMN and ATP to FAD and diphosphate |
| Reaction | FMN + ATP + H+ = FAD + diphosphate |
| Cofactor | Requires Mg2+ or other divalent metal ions for catalysis (as inferred from related adenylyltransferases) |
| Localization | Cytosolic in eukaryotes; cytoplasmic in prokaryotes |
| Representative genes | FLAD1 (human), ribF (E. coli), FADS (S. aureus), AtFADS (Arabidopsis) |
What Is GO:0003919?
According to the Gene Ontology, FMN adenylyltransferase activity (GO:0003919) is defined as the catalysis of the reaction: FMN + ATP + H+ = FAD + diphosphate. In other words, it is the enzyme activity that attaches an adenosine monophosphate (AMP) moiety from ATP to FMN, forming FAD and releasing pyrophosphate. This activity is synonymous with FAD synthetase, FAD pyrophosphorylase, and ATP:FMN adenylyltransferase, among other names. It belongs to the molecular_function ontology aspect and is essential for the final step of FAD biosynthesis.
Why Is FMN adenylyltransferase activity Important in Cell Biology?
FMN adenylyltransferase activity is critical because it produces FAD, a cofactor that is essential for the function of numerous flavoproteins involved in mitochondrial energy production, fatty acid oxidation, and redox homeostasis. Disruption of this activity leads to FAD deficiency, which can impair cellular respiration and has been linked to human disorders such as multiple acyl-CoA dehydrogenase deficiency (MADD) and riboflavin-responsive diseases. In pathogens, the enzyme is a potential drug target because many bacteria rely on a single bifunctional FAD synthetase for survival. In biotechnology, engineering this activity can boost riboflavin overproduction in industrial fermentation. Thus, understanding GO:0003919 has broad implications for medicine, microbiology, and metabolic engineering.
• Provides FAD, an essential cofactor for mitochondrial electron transport and fatty acid oxidation.
• Dysfunction of human FAD synthase (FLAD1) is associated with rare metabolic myopathies and riboflavin-responsive disorders.
• Bacterial FAD synthetases are attractive targets for novel antibiotics due to their essentiality and unique bifunctional architecture.
• Plant FAD synthetases are involved in development, stress responses, and photosynthesis.
• The enzyme is a bottleneck in industrial riboflavin production, and its engineering can enhance yields.
• Structural studies reveal unique catalytic mechanisms that inform inhibitor design.
• CRISPR-based editing of FAD synthetase genes enables functional dissection of its role in metabolism.
• The activity is conserved across all domains of life, making it a model for enzyme evolution studies.
What Happens During FMN adenylyltransferase activity?
Substrate Binding and Recognition
In simple terms: The enzyme grabs FMN and ATP and holds them in the right position to react.
The first step in the catalytic cycle involves binding of the substrates FMN and ATP to the active site of the enzyme. Structural and mutational studies on Staphylococcus aureus FAD synthetase have shown that a conserved phenylalanine residue (F26) plays a crucial role in FMN binding and orientation, and its mutation significantly reduces adenylyltransferase activity. In eukaryotic FMN adenylyltransferases, such as the human enzyme, the active site is formed by a Rossmann-like fold that accommodates both FMN and ATP in a productive conformation. The binding of substrates is often ordered, with FMN binding first, followed by ATP, as suggested by kinetic studies on bacterial and plant enzymes.
Adenylyl Transfer and Catalysis
In simple terms: The enzyme snips off the AMP part of ATP and attaches it to FMN, making FAD.
Once both substrates are bound, the enzyme catalyzes the transfer of the adenylyl group from ATP to the phosphate group of FMN, releasing pyrophosphate (diphosphate) as a byproduct. This reaction proceeds via a direct in-line attack mechanism, where the hydroxyl group of FMN's phosphate acts as a nucleophile on the alpha-phosphate of ATP. Divalent metal ions, typically Mg2+, are required for neutralizing the negative charges of ATP and stabilizing the transition state. Mutagenesis of an arginine residue in the adenylyltransferase module of a prokaryotic bifunctional FAD synthetase affected both the adenylyltransferase and the riboflavin kinase activities, indicating interdomain communication.
Product Release and Cofactor Delivery
In simple terms: The newly made FAD is released and delivered to the proteins that need it.
After catalysis, FAD is released from the active site. In bifunctional enzymes, the FAD product may be channeled directly to downstream flavoproteins or to the riboflavin kinase domain for feedback regulation. In humans, the FAD synthase enzyme (FLAD1) exists in multiple isoforms, some of which are targeted to mitochondria, ensuring FAD delivery to mitochondrial flavoproteins. In plants, a FAD synthetase fused to an inactivated FAD pyrophosphatase domain may play a role in regulating FAD homeostasis. The release step is often rate-limiting and can be influenced by cellular FAD levels.
Regulation by Cellular FAD Levels
In simple terms: When there is enough FAD, the enzyme slows down to avoid waste.
The activity of FMN adenylyltransferase is subject to feedback inhibition by FAD in some organisms. In Listeria monocytogenes, the bifunctional FAD synthetase is regulated by the intracellular FAD concentration, which modulates its kinase and adenylyltransferase activities. Similarly, in Corynebacterium ammoniagenes, overexpression of the bifunctional enzyme increased riboflavin production, but excessive FAD accumulation can inhibit the enzyme. This feedback regulation ensures a balance between FAD synthesis and demand.
Key Genes Involved in GO:0003919 FMN adenylyltransferase activity
The following genes encode proteins with FMN adenylyltransferase activity or are directly involved in its regulation across different organisms.
| Gene | Major Role | Research Relevance |
|---|---|---|
| FLAD1 (human) | Encodes human FAD synthase, a bifunctional enzyme with FMN adenylyltransferase and FAD pyrophosphatase domains | Mutations linked to metabolic myopathy and riboflavin-responsive disorders; target for structural studies |
| ribF (E. coli) | Bifunctional riboflavin kinase/FMN adenylyltransferase | Model for bacterial FAD biosynthesis and antibiotic target |
| FADS (S. aureus) | Bifunctional FAD synthetase | Key residue F26 studied for substrate binding; potential drug target |
| FADS (L. monocytogenes) | Bifunctional FAD synthetase | Regulation by FAD levels; role in virulence |
| FADS (C. ammoniagenes) | Bifunctional riboflavin kinase/FMN adenylyltransferase | Engineered via CRISPR for enhanced riboflavin production |
| AtFADS (Arabidopsis thaliana) | FAD synthetase fused to inactivated FAD pyrophosphatase | Plant FAD homeostasis and stress responses |
| FADS (Bacillus subtilis) | Bifunctional FAD synthetase | Model for Gram-positive FAD metabolism |
| FADS (Streptococcus pneumoniae) | Bifunctional FAD synthetase | Essential for viability; antibiotic target |
| FADS (Mycobacterium tuberculosis) | Bifunctional FAD synthetase | Potential target for anti-tuberculosis drugs |
| FADS (Saccharomyces cerevisiae) | FAD synthetase | Eukaryotic model for FAD biosynthesis |
| FADS (Schizosaccharomyces pombe) | FAD synthetase | Model for mitochondrial FAD transport |
| FADS (Drosophila melanogaster) | FAD synthetase | Developmental roles of FAD |
| FADS (Danio rerio) | FAD synthetase | Vertebrate model for FAD-related disorders |
| FADS (Mus musculus) | FAD synthetase | Knockout models for metabolic studies |
| FADS (Homo sapiens) isoforms | Multiple isoforms targeted to cytosol and mitochondria | Isoform-specific functions in health and disease |
| ribF (Salmonella typhimurium) | Bifunctional FAD synthetase | Virulence and metabolism |
| FADS (Thermus thermophilus) | Bifunctional FAD synthetase | Thermostability and structural studies |
| FADS (Corynebacterium glutamicum) | Bifunctional FAD synthetase | Industrial riboflavin production |
How Is FMN adenylyltransferase activity Regulated?
The activity of FMN adenylyltransferase is regulated at multiple levels. In bacteria, the bifunctional enzyme is often subject to feedback inhibition by FAD, which binds to the adenylyltransferase domain and reduces catalytic efficiency. In Listeria monocytogenes, the FAD synthetase is regulated by the intracellular FAD concentration, which modulates both its kinase and adenylyltransferase activities. In eukaryotes, the human FAD synthase (FLAD1) is expressed as multiple isoforms that are differentially targeted to the cytosol and mitochondria, and their expression is likely regulated by cellular demands for FAD. Additionally, in plants, the fused FAD synthetase-inactivated FAD pyrophosphatase may sense FAD levels and adjust activity accordingly. Transcriptional regulation of FAD synthetase genes has been observed in response to riboflavin availability in some organisms.
FMN adenylyltransferase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| FLAD1 | Multiple acyl-CoA dehydrogenase deficiency (MADD), riboflavin-responsive myopathy | Knockout or point-mutation in human cell lines (e.g., HEK293) and mouse models |
| FADS (S. aureus) | Bacterial infection; essential for survival | CRISPR interference or knockout in S. aureus; mouse infection model |
| FADS (M. tuberculosis) | Tuberculosis | Conditional knockout in M. tuberculosis; macrophage infection model |
| FADS (L. monocytogenes) | Listeriosis; regulation by FAD | Knockout in L. monocytogenes; cell infection assays |
| FADS (C. ammoniagenes) | Industrial riboflavin overproduction | CRISPR/Cas9 site-directed mutagenesis to enhance production |
Metabolic Myopathy and Riboflavin-Responsive Disorders
Mutations in the human FLAD1 gene, which encodes FAD synthase, cause a rare metabolic disorder characterized by multiple acyl-CoA dehydrogenase deficiency (MADD) and lipid storage myopathy. Patients present with muscle weakness, exercise intolerance, and metabolic crises, often responsive to high-dose riboflavin supplementation. The disease underscores the critical role of FMN adenylyltransferase activity in maintaining mitochondrial fatty acid oxidation and energy production.
Infectious Disease and Antibiotic Development
The bifunctional FAD synthetase of pathogenic bacteria such as Staphylococcus aureus, Streptococcus pneumoniae, and Mycobacterium tuberculosis is essential for survival and has no direct human counterpart with the same bifunctional architecture, making it an attractive target for new antibiotics. Inhibitors of FMN adenylyltransferase activity could selectively kill bacteria by blocking FAD biosynthesis.
Cancer and Cellular Metabolism
Altered flavin metabolism has been observed in some cancers, where rapid proliferation increases demand for FAD-dependent enzymes involved in one-carbon metabolism and oxidative phosphorylation. Although direct mutations in FMN adenylyltransferase are not common in cancer, targeting FAD synthesis pathways may offer therapeutic opportunities in cancers with high metabolic flux.
From FMN adenylyltransferase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the effect of complete loss of FMN adenylyltransferase activity on cell viability? | CRISPR knockout of FLAD1 in human cell lines (e.g., HeLa, HEK293) |
| How does a specific point mutation (e.g., F26A) affect catalytic efficiency? | CRISPR point mutation in S. aureus FADS gene, followed by enzyme kinetics |
| Can a tagged version of FAD synthase be used to study subcellular localization? | Knock-in of GFP or FLAG tag at the endogenous FLAD1 locus |
| Does overexpression of FAD synthetase increase FAD levels and affect metabolism? | Overexpression of FADS in C. ammoniagenes or human cells |
| What are the interactors of FAD synthase in mitochondria? | Knock-in of proximity-labeling tags (e.g., APEX2) followed by proteomics |
| Can CRISPR library screening identify synthetic lethal partners of FAD synthase? | Genome-wide CRISPR knockout library in FLAD1-mutant cells |
How to Study the FMN adenylyltransferase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Coupled spectrophotometric assay | FAD formation from FMN and ATP | Kinetic characterization of wild-type and mutant enzymes |
| HPLC flavin analysis | Concentrations of FMN, FAD, and riboflavin | Metabolic profiling of cells with CRISPR edits |
| X-ray crystallography | Three-dimensional structure of enzyme-substrate complexes | Mechanistic studies and inhibitor design |
| CRISPR/Cas9 knockout | Loss-of-function phenotypes | Essentiality testing in pathogens and human cells |
| Site-directed mutagenesis via CRISPR | Effect of specific amino acid changes | Enhancing industrial riboflavin production |
| LC-MS/MS metabolomics | Intracellular flavin levels | Assessing metabolic impact of FAD synthase mutations |
| Proximity labeling proteomics | Protein-protein interactions of FAD synthase | Identifying mitochondrial interaction partners |
| CRISPR library screening | Genome-wide fitness effects | Discovering synthetic lethal interactions |
Enzymatic Assays for FMN Adenylyltransferase Activity
Direct measurement of FMN adenylyltransferase activity is typically performed using a coupled spectrophotometric assay that monitors the formation of FAD from FMN and ATP. The reaction can be followed by the increase in absorbance at 450 nm or by HPLC separation of flavins. Radioactive or fluorescently labeled ATP can also be used to quantify adenylyl transfer. These assays are essential for characterizing mutant enzymes generated by CRISPR editing.
Structural Biology: X-ray Crystallography and Cryo-EM
High-resolution structures of FAD synthetases from bacteria, fungi, and humans have been solved by X-ray crystallography, revealing the architecture of the adenylyltransferase domain and its substrate-binding pockets. Cryo-electron microscopy is increasingly used for large bifunctional complexes. These methods guide mutagenesis studies and inhibitor design.
CRISPR-Based Functional Genomics
CRISPR/Cas9 and CRISPR interference (CRISPRi) enable precise knockout or knockdown of FAD synthetase genes in various organisms. Site-directed mutagenesis via CRISPR has been used to alter specific residues in the C. ammoniagenes FADS gene to enhance riboflavin production. Genome-wide CRISPR screens can identify genes that interact with FAD synthesis pathways.
Metabolomics and Flux Analysis
Quantitative metabolomics using LC-MS/MS can measure intracellular levels of FMN, FAD, and related metabolites in cells with edited FAD synthetase genes. Flux analysis with 13C-labeled precursors can reveal how changes in FMN adenylyltransferase activity affect metabolic networks.
How CRISPR Can Be Used to Study GO:0003919 FMN adenylyltransferase activity
Knockout
CRISPR knockout of FAD synthetase genes (e.g., FLAD1 in human cells or ribF in bacteria) creates null alleles that abolish FMN adenylyltransferase activity. These models are used to study the essentiality of FAD biosynthesis, metabolic rewiring, and compensatory pathways. In human cells, FLAD1 knockout leads to reduced mitochondrial respiration and increased sensitivity to oxidative stress.
Point Mutation
CRISPR-based point mutation allows the introduction of specific amino acid substitutions, such as F26A in S. aureus FADS, to dissect catalytic residues and substrate binding. This approach is valuable for structure-function studies and for engineering enzymes with altered kinetics for industrial applications.
Knock-in
Knock-in of tags (e.g., GFP, FLAG, or APEX2) at the endogenous FAD synthetase locus enables real-time imaging and proximity proteomics. This allows researchers to track subcellular localization and identify interacting proteins in living cells. Knock-in of disease-associated mutations (e.g., FLAD1 mutations) can create isogenic models for studying pathogenic mechanisms.
Overexpression
CRISPR activation (CRISPRa) or traditional overexpression constructs can increase FMN adenylyltransferase levels. Overexpression of FADS in C. ammoniagenes or E. coli is used to boost riboflavin and FAD production in industrial fermentation. In human cells, overexpression can rescue phenotypes of FAD deficiency or study dose-dependent effects.
How EDITGENE Supports FMN adenylyltransferase activity Research
Researchers studying FMN adenylyltransferase activity-related genes often need to determine whether a candidate gene is causally involved in FAD biosynthesis, metabolic regulation, or disease. EDITGENE provides a comprehensive suite of CRISPR-based services to accelerate this research, from knockout and point mutation to knock-in and overexpression, supported by library screening and bioinformatics.
Contact EDITGENE today to design your custom CRISPR model for FMN adenylyltransferase activity research.
Frequently Asked Questions About FMN adenylyltransferase activity
What is FMN adenylyltransferase activity?
FMN adenylyltransferase activity (GO:0003919) is the enzyme activity that catalyzes the conversion of FMN and ATP to FAD and diphosphate, the final step in FAD biosynthesis.
What genes are involved in FMN adenylyltransferase activity?
Key genes include FLAD1 in humans, ribF in E. coli, FADS in Staphylococcus aureus, and AtFADS in Arabidopsis, among others.
What is the reaction catalyzed by FMN adenylyltransferase?
The reaction is FMN + ATP + H+ = FAD + diphosphate, producing the essential cofactor FAD.
What diseases are associated with FMN adenylyltransferase dysfunction?
Mutations in human FLAD1 cause multiple acyl-CoA dehydrogenase deficiency (MADD) and riboflavin-responsive myopathy. Bacterial enzymes are targets for antibiotics.
How is FMN adenylyltransferase activity regulated?
It is regulated by feedback inhibition by FAD and by transcriptional control in response to riboflavin availability.
What is the difference between FAD synthetase and FMN adenylyltransferase?
FAD synthetase is a common name for the enzyme; FMN adenylyltransferase is the official GO term for its catalytic activity.
Can CRISPR be used to study FMN adenylyltransferase?
Yes, CRISPR knockout, point mutation, and knock-in models are powerful tools to dissect the function of FAD synthetase genes.
What model organisms are used to study FMN adenylyltransferase?
Common models include E. coli, S. aureus, C. ammoniagenes, S. cerevisiae, Arabidopsis, and human cell lines.
What are the industrial applications of FMN adenylyltransferase?
Engineering the enzyme can enhance riboflavin and FAD production in fermentation processes.
How can I measure FMN adenylyltransferase activity in the lab?
Activity can be measured using coupled spectrophotometric assays, HPLC, or LC-MS/MS to quantify FAD formation.
Conclusion
FMN adenylyltransferase activity (GO:0003919) is a fundamental enzymatic function responsible for the final step of FAD biosynthesis, impacting energy metabolism, redox biology, and human health. Its structural and mechanistic diversity across organisms offers rich opportunities for drug discovery and metabolic engineering. CRISPR-based tools now enable precise interrogation of this activity in diverse biological contexts, from bacterial pathogens to human cells. Continued research on this enzyme will illuminate new therapeutic and biotechnological applications.
References
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- 2. Fu B et al.. 2024. Site-directed mutagenesis of bifunctional riboflavin kinase/FMN adenylyltransferase via CRISPR/Cas9 to enhance riboflavin production.. Synth Syst Biotechnol 9(3):503-512 PMID: 38680946
- 3. Sebastián M et al.. 2019. The Biosynthesis of Flavin Cofactors in Listeria monocytogenes.. J Mol Biol 431(15):2762-2776 PMID: 31132361
- 4. Serrano A et al.. 2015. Quaternary organization in a bifunctional prokaryotic FAD synthetase: Involvement of an arginine at its adenylyltransferase module on the riboflavin kinase activity.. Biochim Biophys Acta 1854(8):897-906 PMID: 25801930
- 5. Serrano A et al.. 2013. The prokaryotic FAD synthetase family: a potential drug target.. Curr Pharm Des 19(14):2637-48 PMID: 23116401
- 6. Huerta C et al.. 2009. Structure and mechanism of a eukaryotic FMN adenylyltransferase.. J Mol Biol 389(2):388-400 PMID: 19375431
- 7. Leo G et al.. 2024. Structural insights into the bifunctional enzyme human FAD synthase.. Structure 32(7):953-965.e5 PMID: 38688286
- 8. Lynch JH et al.. 2022. A higher plant FAD synthetase is fused to an inactivated FAD pyrophosphatase.. J Biol Chem 298(12):102626 PMID: 36273586
