GO:0004315 3-oxoacyl-[acyl-carrier-protein] synthase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0004315 describes the condensing enzyme activity that catalyzes the reaction acyl-[acyl-carrier protein] + malonyl-[acyl-carrier protein] = 3-oxoacyl-[acyl-carrier protein] + CO2 + [acyl-carrier protein].
• This activity is a core component of type II fatty acid biosynthesis and is essential for producing the acyl chains used in membrane lipids and energy storage.
• The reaction proceeds through a ping-pong mechanism involving an acyl-enzyme intermediate and decarboxylation of malonyl-ACP.
• Key genes encoding this activity include KAS I, KAS II, and KAS III (e.g., FabB, FabF, FabH in bacteria; OXSM in mitochondria).
• Dysregulation of 3-oxoacyl-ACP synthase activity is linked to metabolic disorders, cancer, and microbial pathogenesis, making it a target for antibiotics and herbicides.
• CRISPR-based knockout, point mutation, and overexpression models enable precise dissection of this activity in health and disease.
Description
3-oxoacyl-[acyl-carrier-protein] synthase activity (GO:0004315) is a molecular function that catalyzes the condensation of an acyl-[acyl-carrier protein] with malonyl-[acyl-carrier protein] to form a 3-oxoacyl-[acyl-carrier protein], releasing carbon dioxide and free acyl-carrier protein. This reaction is a central step in the type II fatty acid synthase (FAS II) pathway, which is responsible for de novo fatty acid biosynthesis in bacteria, plants, and mitochondria. The activity is essential for generating the acyl chains that serve as building blocks for membrane lipids, lipoic acid, and energy storage molecules. Researchers study GO:0004315 because it represents a critical node in lipid metabolism and a validated target for antibiotics, herbicides, and anti-obesity strategies. In bacteria, the enzyme is the target of natural products such as thiolactomycin and platensimycin, which inhibit fatty acid synthesis and exhibit antibacterial activity. In plants, specific isoforms like KAS I are targeted by herbicides, affecting chloroplast fatty acid production. In humans, mitochondrial fatty acid synthesis (mtFASII) involves OXSM, a 3-oxoacyl-ACP synthase, and its dysfunction has been linked to ferroptosis and ischemia/reperfusion injury. Understanding the molecular details, regulation, and disease relevance of GO:0004315 requires integrating structural biology, enzymology, and genetic models. This article synthesizes authoritative QuickGO annotations and verified PubMed literature to provide a comprehensive overview for researchers aiming to study or target this activity.
3-oxoacyl-[acyl-carrier-protein] synthase activity At A Glance
| GO ID | GO:0004315 |
|---|---|
| GO term | 3-oxoacyl-[acyl-carrier-protein] synthase activity |
| Ontology | molecular_function |
| Synonym | 3-ketoacyl-acyl carrier protein synthase activity; beta-ketoacyl-ACP synthase activity; condensing enzyme activity |
| Major function | Catalyzes the condensation of acyl-ACP and malonyl-ACP to form 3-oxoacyl-ACP, CO2, and ACP |
| Reaction | acyl-[acyl-carrier protein] + malonyl-[acyl-carrier protein] = 3-oxoacyl-[acyl-carrier protein] + CO2 + [acyl-carrier protein] |
| Pathway | Fatty acid biosynthesis (FAS II) |
| EC number | 2.3.1.41 (acyl-[acyl-carrier-protein]:malonyl-[acyl-carrier-protein] C-acyltransferase (decarboxylating)) |
What Is GO:0004315?
GO:0004315 is defined as the catalysis of the reaction: acyl-[acyl-carrier protein] + malonyl-[acyl-carrier protein] = 3-oxoacyl-[acyl-carrier protein] + CO2 + [acyl-carrier protein]. In simpler terms, it is the enzyme activity that joins a growing fatty acid chain (attached to acyl-carrier protein) with a two-carbon unit from malonyl-ACP, while releasing carbon dioxide. This condensation reaction is also known as 3-ketoacyl-ACP synthase, beta-ketoacyl-ACP synthase, or condensing enzyme activity. The activity is found in type II fatty acid synthase systems and is distinct from the multifunctional type I FAS found in mammals.
Why Is 3-oxoacyl-[acyl-carrier-protein] synthase activity Important in Cell Biology?
GO:0004315 is fundamentally important because it catalyzes the committed step of fatty acid elongation in type II FAS, a pathway essential for membrane biogenesis and energy homeostasis in bacteria, plants, and mitochondria. Inhibiting this activity with small molecules such as thiolactomycin or platensimycin analogues effectively blocks bacterial growth, validating it as an antibiotic target. In agriculture, herbicides like ferulic acid ethyl ester target KAS I to disrupt plant fatty acid synthesis. In human health, the mitochondrial isoform OXSM is implicated in ferroptosis and ischemia/reperfusion injury, highlighting its role in disease. Thus, understanding GO:0004315 offers opportunities for therapeutic intervention across infectious diseases, metabolic disorders, and cancer.
• Essential for bacterial membrane lipid synthesis and viability, making it a prime antibiotic target.
• Target of herbicides that inhibit plant KAS I, affecting crop growth.
• Involved in mitochondrial fatty acid synthesis (mtFASII) and linked to ferroptosis in ischemia/reperfusion injury.
• Regulates energy metabolism through long-chain fatty acid production.
• Provides a model system for studying enzyme mechanisms like ping-pong kinetics and decarboxylation.
• Structural studies of KAS II from Thermus thermophilus reveal conserved folds for drug design.
• Dysregulation may contribute to metabolic diseases such as obesity and diabetes.
• Platensimycin analogues with improved activity highlight its druggability.
• Key enzyme for producing precursors of lipoic acid and quorum-sensing molecules.
• Enables CRISPR-based functional genomics to dissect its role in various organisms.
What Happens During 3-oxoacyl-[acyl-carrier-protein] synthase activity?
Substrate Binding and Acyl-Enzyme Formation
In simple terms: The enzyme first grabs a fatty acid chain and holds it tightly.
The catalytic cycle begins with the binding of an acyl-[acyl-carrier protein] (acyl-ACP) substrate to the enzyme. The acyl group is transferred to a conserved cysteine residue in the active site, forming a covalent acyl-enzyme intermediate and releasing the acyl-carrier protein (ACP). This step is essential for priming the enzyme for the subsequent condensation reaction.
Decarboxylation of Malonyl-ACP
In simple terms: A second molecule loses a carbon dioxide piece, becoming reactive.
Next, malonyl-[acyl-carrier protein] (malonyl-ACP) binds to the enzyme. The enzyme catalyzes the decarboxylation of malonyl-ACP, generating a reactive carbanion that attacks the acyl-enzyme intermediate. This decarboxylation drives the condensation by providing the necessary energy and is a hallmark of 3-oxoacyl-ACP synthase activity.
Condensation and Product Release
In simple terms: The two pieces join together, and the new chain is released.
The carbanion from malonyl-ACP attacks the acyl-enzyme, forming a new carbon-carbon bond and yielding a 3-oxoacyl-[acyl-carrier protein] product. The product is released, and the free enzyme is regenerated for another cycle. This elongation step adds two carbons to the growing fatty acid chain, which is then further processed by other FAS enzymes.
Role in Fatty Acid Elongation Cycle
In simple terms: This is one step in a repeating cycle that builds fatty acids.
The 3-oxoacyl-ACP product undergoes subsequent reduction, dehydration, and reduction reactions to form a saturated acyl-ACP, which can then re-enter the cycle for another round of elongation. The activity of 3-oxoacyl-ACP synthase determines the rate and specificity of chain elongation, influencing the final fatty acid composition.
Key Genes Involved in GO:0004315 3-oxoacyl-[acyl-carrier-protein] synthase activity
The following genes encode proteins with 3-oxoacyl-[acyl-carrier-protein] synthase activity or are directly involved in its regulation and function.
| Gene | Major Role | Research Relevance |
|---|---|---|
| FabB (KAS I) | Beta-ketoacyl-ACP synthase I in E. coli; elongates unsaturated fatty acids | Target of thiolactomycin; model for enzyme kinetics |
| FabF (KAS II) | Beta-ketoacyl-ACP synthase II; elongates saturated fatty acids | Structural studies; antibiotic target |
| FabH (KAS III) | Initiates fatty acid synthesis by condensing acetyl-CoA with malonyl-ACP | Essential for bacterial viability; drug target |
| OXSM | Mitochondrial 3-oxoacyl-ACP synthase; involved in mtFASII | Linked to ferroptosis and ischemia/reperfusion injury |
| KAS I (plant) | Chloroplast 3-oxoacyl-ACP synthase; involved in de novo fatty acid synthesis | Herbicide target; studied in Cuphea wrightii |
| KAS II (plant) | Chloroplast 3-oxoacyl-ACP synthase; elongates palmitic acid | Role in plant lipid metabolism |
| KAS III (plant) | Initiates fatty acid synthesis in plastids | Mechanistic studies |
| mtKAS | Mitochondrial KAS in yeast and humans | Model for mitochondrial fatty acid synthesis |
| FabB/FabF homologs | Bacterial condensing enzymes | Antibiotic discovery |
| KasA | Mycobacterial 3-oxoacyl-ACP synthase | Target for anti-tuberculosis drugs |
| KasB | Mycobacterial 3-oxoacyl-ACP synthase | Involved in mycolic acid synthesis |
| ACP | Acyl-carrier protein; substrate carrier | Essential for all FAS reactions |
| MCAT | Malonyl-CoA:ACP transacylase; provides malonyl-ACP | Upstream of GO:0004315 |
| FabD | Malonyl-CoA:ACP transacylase in bacteria | Generates substrate for condensation |
| FabH (mt) | Mitochondrial KAS III | Initiates mtFASII |
| LipA | Lipoic acid synthase; requires 3-oxoacyl-ACP | Links FAS to cofactor biosynthesis |
| FabI | Enoyl-ACP reductase; downstream of condensation | Target of triclosan |
| FabZ | Dehydratase; acts after condensation | Part of FAS II cycle |
How Is 3-oxoacyl-[acyl-carrier-protein] synthase activity Regulated?
The activity of 3-oxoacyl-[acyl-carrier-protein] synthase is regulated at multiple levels. In bacteria, the expression of fab genes is controlled by the FadR and FabR transcription factors in response to fatty acid availability. In plants, KAS I and KAS II are regulated by light and developmental signals, affecting chloroplast fatty acid synthesis. In mitochondria, OXSM expression is influenced by metabolic stress and the lactate-primed KAT8-PCK2 axis, which reprograms OXSM-dependent mitochondrial fatty acid synthesis during ischemia/reperfusion injury. Additionally, the activity can be feedback-inhibited by long-chain acyl-ACPs. These regulatory mechanisms ensure that fatty acid production matches cellular demands.
3-oxoacyl-[acyl-carrier-protein] synthase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| OXSM | Hepatic ferroptosis in ischemia/reperfusion injury | Knockout mouse model; overexpression in hepatocytes |
| FabB/FabH | Bacterial infections; antibiotic target | Bacterial knockout strains; inhibitor screening |
| KasA/KasB | Mycobacterial infections (tuberculosis) | Mycobacterial knockout; platensimycin analogues |
| KAS I (plant) | Herbicide susceptibility | Plant knockout or point mutation; herbicide treatment |
| FabF | Bacterial membrane integrity | Structural studies; mutant complementation |
Metabolic Disorders and Ferroptosis
Dysregulation of mitochondrial fatty acid synthesis, including OXSM (a 3-oxoacyl-ACP synthase), has been implicated in hepatic ferroptosis during ischemia/reperfusion injury. The lactate-primed KAT8-PCK2 axis exacerbates this injury by reprogramming OXSM-dependent mtFASII, leading to lipid peroxidation and cell death. This suggests that targeting GO:0004315 activity could mitigate ferroptosis in ischemic diseases.
Bacterial Infections and Antibiotic Resistance
Bacterial 3-oxoacyl-ACP synthases are essential for membrane lipid biosynthesis and are validated targets for antibiotics. Thiolactomycin inhibits FabB and FabH, while platensimycin analogues show improved antimycobacterial activity by targeting KasA/KasB. The emergence of antibiotic resistance underscores the need for novel inhibitors of this activity.
Cancer and Metabolic Reprogramming
Cancer cells often exhibit altered lipid metabolism to support rapid proliferation. Although direct mutations in 3-oxoacyl-ACP synthase genes are rare in cancer, the pathway is upregulated in some tumors. Long-chain fatty acids regulate energy metabolism and can influence cancer cell signaling. Targeting mitochondrial fatty acid synthesis may offer therapeutic opportunities.
Plant Herbicide Resistance
In agriculture, herbicides such as ferulic acid ethyl ester target plant KAS I, disrupting fatty acid synthesis and causing growth inhibition. Understanding the mechanism of GO:0004315 in plants can guide the development of new herbicides and management of resistance.
From 3-oxoacyl-[acyl-carrier-protein] synthase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of OXSM cause ferroptosis? | OXSM knockout cell line (e.g., HepG2) |
| Can point mutations in FabB alter substrate specificity? | Site-directed mutagenesis; bacterial expression |
| Does overexpression of KAS I increase fatty acid production? | Plant overexpression lines |
| Can tagged KAS II be used for localization studies? | Knock-in of FLAG-tag in Thermus thermophilus |
| Is FabH essential for bacterial viability? | Conditional knockout in E. coli |
| Can CRISPR library screening identify synthetic lethal partners? | Genome-wide KO library in cancer cells |
How to Study the 3-oxoacyl-[acyl-carrier-protein] synthase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Radioactive malonyl-ACP decarboxylation assay | Enzyme activity | Kinetic studies and inhibitor screening |
| X-ray crystallography | Three-dimensional structure | Active site analysis and drug design |
| CRISPR-Cas9 knockout | Gene function | Essentiality and disease models |
| Site-directed mutagenesis | Residue-specific effects | Mechanistic studies |
| RNA-seq | Transcriptional changes | Pathway regulation and disease |
| Lipidomics | Fatty acid composition | Metabolic impact |
| Western blot | Protein expression | Validation of knockout/overexpression |
| In vitro inhibition assays | IC50 of inhibitors | Antibiotic/herbicide discovery |
Enzymatic Assays for Condensing Activity
Direct measurement of 3-oxoacyl-ACP synthase activity uses spectrophotometric or radioactive assays that monitor the condensation of acyl-ACP and malonyl-ACP. For example, the release of CO2 or the formation of 3-oxoacyl-ACP can be quantified. These assays are essential for kinetic characterization and inhibitor screening.
Structural Biology and Crystallography
X-ray crystallography of 3-oxoacyl-ACP synthases, such as KAS II from Thermus thermophilus, reveals the active site architecture and substrate binding pockets. These structures guide the design of specific inhibitors and help understand catalytic mechanisms.
Genetic Knockout and Complementation
Knockout of genes encoding 3-oxoacyl-ACP synthases (e.g., fabB, fabF, OXSM) in bacteria, plants, or mammalian cells, followed by complementation with wild-type or mutant alleles, can establish essentiality and structure-function relationships. CRISPR-Cas9 facilitates rapid generation of such models.
Omics Approaches to Study Pathway Flux
Transcriptomics, proteomics, and lipidomics can assess the impact of altered 3-oxoacyl-ACP synthase activity on global fatty acid profiles and gene expression. For instance, RNA-seq of OXSM knockout cells reveals changes in ferroptosis-related genes. Metabolomics can quantify acyl-ACP intermediates.
How CRISPR Can Be Used to Study GO:0004315 3-oxoacyl-[acyl-carrier-protein] synthase activity
Knockout
CRISPR-Cas9 knockout of genes encoding 3-oxoacyl-ACP synthases (e.g., OXSM, FabB, KAS I) enables researchers to assess their essentiality and contribution to fatty acid synthesis. For example, OXSM knockout in hepatic cells exacerbates ferroptosis under ischemia/reperfusion conditions. In bacteria, conditional knockouts of fabB or fabH can reveal growth defects and validate antibiotic targets.
Point Mutation
Introducing specific point mutations in the catalytic residues (e.g., the active-site cysteine) of 3-oxoacyl-ACP synthases via CRISPR base editing or homology-directed repair allows precise dissection of the enzymatic mechanism. Such mutants can be tested for loss of condensation activity and used to study substrate specificity.
Knock-in
Knock-in of epitope tags (e.g., FLAG, HA) or fluorescent proteins at the endogenous locus of 3-oxoacyl-ACP synthase genes facilitates localization, interaction, and real-time activity studies. For instance, tagging KAS II in Thermus thermophilus enabled structural studies. Knock-in of disease-associated variants can model human disorders.
Overexpression
CRISPR activation (CRISPRa) or transgenic overexpression of 3-oxoacyl-ACP synthase genes can increase fatty acid production, useful for metabolic engineering and studying pathway flux. Overexpression of plant KAS I in crops may enhance oil content, while overexpression of OXSM can modulate ferroptosis sensitivity.
How EDITGENE Supports 3-oxoacyl-[acyl-carrier-protein] synthase activity Research
Researchers studying 3-oxoacyl-[acyl-carrier-protein] synthase activity-related genes often need to determine whether a candidate gene is causally involved in fatty acid metabolism, disease progression, or drug response. EDITGENE provides comprehensive CRISPR-based services to generate precisely engineered cell models, enabling functional validation and mechanistic studies.
Contact EDITGENE today to design your custom CRISPR model for 3-oxoacyl-[acyl-carrier-protein] synthase activity research.
Frequently Asked Questions About 3-oxoacyl-[acyl-carrier-protein] synthase activity
What is 3-oxoacyl-[acyl-carrier-protein] synthase activity?
It is the enzyme activity (GO:0004315) that catalyzes the condensation of acyl-ACP and malonyl-ACP to form 3-oxoacyl-ACP, CO2, and ACP, a key step in fatty acid biosynthesis.
What genes are involved in 3-oxoacyl-[acyl-carrier-protein] synthase activity?
Key genes include FabB (KAS I), FabF (KAS II), FabH (KAS III) in bacteria, OXSM in mitochondria, and KAS I/II/III in plants.
What is the reaction catalyzed by GO:0004315?
The reaction is: acyl-[acyl-carrier protein] + malonyl-[acyl-carrier protein] = 3-oxoacyl-[acyl-carrier protein] + CO2 + [acyl-carrier protein].
How is 3-oxoacyl-ACP synthase activity regulated?
It is regulated by transcription factors (e.g., FadR, FabR), feedback inhibition by acyl-ACPs, and metabolic signals such as the lactate-primed KAT8-PCK2 axis in mitochondria.
What diseases are associated with 3-oxoacyl-ACP synthase dysfunction?
Dysfunction is linked to bacterial infections (antibiotic target), plant herbicide resistance, and hepatic ferroptosis in ischemia/reperfusion injury via OXSM.
What is the difference between KAS I, KAS II, and KAS III?
KAS III initiates fatty acid synthesis by condensing acetyl-CoA with malonyl-ACP; KAS I and KAS II elongate the growing chain, with preferences for unsaturated and saturated substrates, respectively.
How can I study 3-oxoacyl-ACP synthase activity in the lab?
Common methods include enzymatic assays, X-ray crystallography, CRISPR knockout, site-directed mutagenesis, and omics approaches like RNA-seq and lipidomics.
What is the role of OXSM in human health?
OXSM is a mitochondrial 3-oxoacyl-ACP synthase involved in mtFASII; its dysregulation exacerbates ferroptosis during ischemia/reperfusion injury.
Can CRISPR be used to target 3-oxoacyl-ACP synthase genes?
Yes, CRISPR-Cas9 can generate knockout, point mutation, knock-in, and overexpression models for genes like OXSM, FabB, and KAS I to study their function.
What inhibitors target 3-oxoacyl-ACP synthase activity?
Thiolactomycin inhibits FabB and FabH, while platensimycin analogues target mycobacterial KasA/KasB; ferulic acid ethyl ester targets plant KAS I.
Conclusion
3-oxoacyl-[acyl-carrier-protein] synthase activity (GO:0004315) is a fundamental enzymatic function in fatty acid biosynthesis, with critical roles in bacterial viability, plant lipid metabolism, and human mitochondrial function. Its conservation across kingdoms and druggability make it a prime target for antibiotics, herbicides, and metabolic therapeutics. Advances in CRISPR-based genome editing and structural biology continue to unravel its mechanistic details and disease connections. Researchers can leverage EDITGENE's comprehensive services to generate precise cell models and accelerate discoveries related to this essential activity.
References
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