# ACACB Gene: Structure, Function, and Clinical Significance


## Key Takeaways

- The *ACACB* gene encodes acetyl-CoA carboxylase beta (ACC2), a mitochondrial enzyme that catalyzes the formation of malonyl-CoA, a critical inhibitor of carnitine palmitoyltransferase 1 (CPT1). This regulatory axis governs the rate-limiting step of mitochondrial fatty acid oxidation (FAO), directly impacting cellular energy homeostasis and lipid partitioning.
- ACC2 is primarily localized to the outer mitochondrial membrane, enabling localized malonyl-CoA production to suppress CPT1-mediated fatty acid import into the mitochondrial matrix, thereby gating β-oxidation. This precise localization is crucial for integrating metabolic signals.
- Genetic variations, particularly the intronic SNP rs2268388, are strongly associated with an increased risk of diabetic nephropathy (DN) in type 2 diabetes mellitus (T2DM) patients, likely due to elevated ACACB expression leading to renal lipotoxicity and inflammation.
- The expression and activity of ACACB are tightly regulated by multiple signaling pathways, including AMPK (inactivation via phosphorylation), SREBP-1c (transcriptional repression by insulin), and PPARs (transcriptional activation by fatty acids), reflecting its central role in metabolic flexibility.
- ACC2 is a validated therapeutic target for metabolic disorders, with small-molecule inhibitors like ND-630 (Firsocostat) and TOFA (5-(tetradecyloxy)-2-furoic acid) being developed to increase FAO and improve insulin sensitivity in conditions such as non-alcoholic steatohepatitis (NASH) and obesity.

---

## Executive Summary & Key Metadata

The **ACACB** gene encodes acetyl-CoA carboxylase beta (ACC2), the rate-limiting enzyme in the mitochondrial fatty acid oxidation (FAO) pathway. ACC2 catalyzes the ATP-dependent carboxylation of acetyl-CoA to produce malonyl-CoA, a potent allosteric inhibitor of carnitine palmitoyltransferase 1 (CPT1). By localizing to the outer mitochondrial membrane, ACC2 generates a local malonyl-CoA pool that suppresses CPT1-mediated import of long-chain fatty acyl-CoA into the mitochondrial matrix, thereby gating β-oxidation. This regulatory node positions ACACB as a central integrator of energy homeostasis, insulin sensitivity, and lipid partitioning across multiple tissues, including skeletal muscle, heart, liver, and adipose tissue.

The gene has been implicated in a broad spectrum of human pathologies, including type 2 diabetes mellitus (T2DM), diabetic nephropathy (DN), obesity, cardiovascular disease, and multiple cancer types. Single-nucleotide polymorphisms (SNPs) within the promoter, 5' untranslated region (UTR), and coding sequence have been reproducibly associated with metabolic traits, and the gene product is an active target for small-molecule inhibitor development aimed at treating obesity, diabetes, and metabolic syndrome.

| **Attribute** | **Value** |
|---|---|
| HGNC Symbol | ACACB |
| UniProt Accession | O00763 |
| Representative PDB ID | true (see Section 2) |
| Chromosomal Locus | 12q24.11 (GRCh38: chr12:109,360,000–109,520,000) |
| Primary Molecular Function | Acetyl-CoA carboxylase activity (ATP-dependent carboxylation of acetyl-CoA to malonyl-CoA); negative regulator of mitochondrial fatty acid oxidation |
| Disease & Pathology Associations | Type 2 diabetes, diabetic nephropathy, obesity, hyperlipidemia, cardiovascular disease, multiple cancers (breast, colorectal, renal, ovarian, glioblastoma), intracranial aneurysm, osteoarthritis, Alzheimer's disease |
| Expression Pattern | High in heart, skeletal muscle, liver, adipose tissue; lower in brain, kidney, pancreas |
| Subcellular Localization | Outer mitochondrial membrane (predominant), cytosol |
| Isoforms | Multiple splice variants; predominant isoforms include ACC2-1 (full-length) and ACC2-2 (N-terminal truncated) |

---

## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Chromosomal Localization and Gene Structure

The human *ACACB* gene is located on the long arm of chromosome 12 at cytogenetic band **12q24.11**. The reference genome assembly (GRCh38) places the gene between approximately 109,360,000 and 109,520,000 base pairs on the forward strand. The gene spans roughly 160 kilobases of genomic DNA and contains **54 exons** and **53 introns**, with the coding sequence distributed across exons 2 through 54. The first exon is non-coding and contributes to the 5' UTR.

The genomic organization of *ACACB* is highly conserved across mammals. Comparative genomics reveals syntenic regions on mouse chromosome 5, rat chromosome 12, and bovine chromosome 5. The gene's large size and complex intronic architecture render it susceptible to alternative splicing and regulatory variation.

### 1.2 Promoter Architecture and Regulatory Elements

The promoter region of *ACACB* lacks a canonical TATA box but contains multiple GC-rich regions and CpG islands, consistent with housekeeping-like regulation that is nevertheless tissue-specific and metabolically responsive. Functional promoter analysis has identified several critical cis-regulatory elements:

- **Sp1 binding sites**: Multiple GC-boxes within the proximal promoter (−200 to −50 bp relative to the transcription start site) are bound by specificity protein 1 (Sp1), which is required for basal transcription.
- **SREBP response elements (SREs)**: Sterol regulatory element-binding proteins (SREBP-1c and SREBP-2) bind to E-box-like sequences in the promoter, linking ACACB transcription to cellular sterol and lipid status.
- **PPAR response elements (PPREs)**: Peroxisome proliferator-activated receptor (PPAR) isoforms, particularly PPARα and PPARδ, bind to DR-1-type response elements and activate transcription in response to fatty acid ligands.
- **ChREBP binding sites**: Carbohydrate-responsive element-binding protein (ChREBP) binds to ChoRE motifs, enabling glucose-dependent transcriptional activation.
- **Glucocorticoid response elements (GREs)**: Partial GREs have been identified, mediating glucocorticoid-induced upregulation in liver and adipose tissue.

A functional SNP in the promoter region, **rs2241220**, has been shown to alter transcription factor binding affinity and reporter gene expression in vitro [<a href="#ref-1">1</a>]. This variant is located within a putative Sp1 binding site and is associated with altered ACACB mRNA levels in human adipose tissue [<a href="#ref-2">2</a>].

### 1.3 Enhancer Elements and Chromatin Architecture

Chromatin conformation capture studies (Hi-C, ChIA-PET) in human tissues have identified several putative enhancer elements within introns 1, 3, and 7 of *ACACB*. These enhancers physically interact with the promoter in a tissue-specific manner, particularly in skeletal muscle and liver. The intronic enhancer within intron 3 contains binding sites for myocyte enhancer factor-2 (MEF2), explaining the high expression of ACACB in cardiac and skeletal muscle.

DNA methylation at CpG sites in the proximal promoter is inversely correlated with ACACB expression. In White Leghorn chickens, methylation of the partial promoter region was associated with reduced ACACB mRNA levels at 18 and 40 weeks of age, demonstrating epigenetic regulation of this gene [<a href="#ref-3">3</a>]. Similar methylation-sensitive regulation is likely operative in mammals.

### 1.4 Alternative Splicing and Isoform Diversity

Alternative splicing of *ACACB* generates multiple transcript variants. The two most extensively characterized isoforms are:

- **Isoform 1 (ACC2-1)**: The full-length protein of 2,458 amino acids, predominantly expressed in heart, skeletal muscle, and liver. This isoform contains the complete N-terminal mitochondrial targeting sequence and is anchored to the outer mitochondrial membrane.
- **Isoform 2 (ACC2-2)**: A shorter variant lacking exons 1–4, resulting in a protein of approximately 2,300 amino acids. This isoform lacks the mitochondrial targeting sequence and is predominantly cytosolic.

Additional minor splice variants have been catalogued in Ensembl and RefSeq, including isoforms with alternative 3' UTRs that differ in mRNA stability and microRNA binding sites. The 3' UTR of the major transcript is approximately 4.5 kb and contains multiple AU-rich elements (AREs) and binding sites for miR-145-5p, miR-33a/b, and miR-19a/b, which post-transcriptionally regulate ACACB expression [<a href="#ref-4">4</a>].

### 1.5 Tissue-Specific Expression

ACACB mRNA is most abundant in tissues with high oxidative capacity: heart, skeletal muscle (particularly type I oxidative fibers), brown adipose tissue, and liver. Moderate expression is observed in white adipose tissue, kidney, and pancreas. In the brain, ACACB is expressed in astrocytes and, to a lesser extent, neurons, where it participates in fatty acid oxidation and ketone body metabolism [<a href="#ref-5">5</a>].

Expression is dynamically regulated by nutritional status: fasting upregulates ACACB in liver and muscle via PPARα and glucocorticoid signaling, while feeding suppresses expression via insulin-dependent SREBP-1c downregulation. In chickens, ACACB expression peaks during the pre-hatch period and declines post-hatch, correlating with the metabolic switch from lipid-based to carbohydrate-based energy metabolism [<a href="#ref-6">6</a>].

---

## 2. 3D Protein Domain Architecture & Structural Biology

### 2.1 Overall Architecture

The ACC2 protein (UniProt O00763) is a large, multifunctional enzyme of 2,458 amino acids (~280 kDa). It comprises three functional domains connected by flexible linkers:

1. **Biotin carboxylase (BC) domain** (residues ~1–600)
2. **Biotin carboxyl carrier protein (BCCP) domain** (residues ~600–800)
3. **Carboxyltransferase (CT) domain** (residues ~800–2,458)

The enzyme functions as a homodimer, with the BC domain of one monomer interacting with the BCCP domain of the other, enabling the two-step catalytic reaction: (i) ATP-dependent carboxylation of the biotin cofactor attached to BCCP, and (ii) transfer of the carboxyl group from carboxybiotin to acetyl-CoA, forming malonyl-CoA.

### 2.2 N-Terminal Mitochondrial Targeting and Membrane Anchoring

The N-terminus (residues 1–150) contains a mitochondrial targeting sequence (MTS) that directs the protein to the outer mitochondrial membrane. Unlike ACC1 (the cytosolic isoform encoded by *ACACA*), ACC2 possesses a 200-amino-acid N-terminal extension that includes a transmembrane helix (residues 20–40). This helix anchors ACC2 to the outer mitochondrial membrane, positioning the catalytic domains in the cytosol while the BCCP domain can interact with the membrane surface. This membrane localization is critical for the functional coupling between ACC2-generated malonyl-CoA and CPT1, which resides in the outer mitochondrial membrane.

### 2.3 Biotin Carboxylase Domain

The BC domain (residues 1–600) adopts a mixed α/β fold characteristic of the ATP-grasp superfamily. Key structural features include:

- **ATP-binding pocket**: Located at the interface between the N-terminal and C-terminal subdomains, coordinating ATP via conserved residues (e.g., Gly-Gly-Gly-L-Gly motifs). The pocket binds Mg²⁺ as a cofactor.
- **Biotin-binding site**: A deep cleft that accommodates the biotinyl-lysine of BCCP, positioning the N1' nitrogen of biotin for nucleophilic attack on the γ-phosphate of ATP.
- **Dimerization interface**: The BC domain dimerizes through an extensive hydrophobic interface, forming a stable homodimer that is catalytically required.

### 2.4 Biotin Carboxyl Carrier Protein Domain

The BCCP domain (residues 600–800) is a small, predominantly β-sheet domain that carries the covalently attached biotin cofactor. The biotin is linked via an amide bond to the ε-amino group of a specific lysine residue (Lys-786 in human ACC2). The BCCP domain is highly mobile, shuttling between the BC and CT active sites during catalysis. This swinging-arm mechanism is essential for the two-step carboxylation reaction.

### 2.5 Carboxyltransferase Domain

The CT domain (residues 800–2,458) is the largest domain and catalyzes the transfer of the carboxyl group from carboxybiotin to acetyl-CoA. The CT domain is further subdivided into:

- **N-terminal CT subdomain (CT-N)**: Residues 800–1,400, containing the acetyl-CoA binding site.
- **C-terminal CT subdomain (CT-C)**: Residues 1,400–2,458, containing the carboxybiotin binding site.

The active site is located at the interface between CT-N and CT-C, forming a tunnel that accommodates both substrates. The reaction proceeds via a biotin-mediated enolate mechanism: the N1' of carboxybiotin abstracts a proton from the methyl group of acetyl-CoA, generating an enolate that attacks the carboxyl group, yielding malonyl-CoA.

### 2.6 Allosteric Regulation and Ligand Binding Sites

ACC2 is subject to allosteric regulation by several metabolites:

- **Citrate**: Binds to an allosteric site in the BC domain, promoting the inactive-to-active conformational transition. Citrate stabilizes the dimeric form and increases catalytic efficiency.
- **Palmitoyl-CoA**: Binds to the same allosteric site as citrate but exerts the opposite effect, promoting dissociation of the dimer and enzyme inactivation.
- **Malonyl-CoA**: Product inhibition occurs at high concentrations, providing negative feedback.

### 2.7 Phosphorylation Sites

ACC2 is regulated by reversible phosphorylation at multiple serine residues:

- **Ser-222** (equivalent to Ser-79 in ACC1): Phosphorylated by AMP-activated protein kinase (AMPK), leading to enzyme inactivation. This is the primary regulatory phosphorylation site.
- **Ser-76, Ser-77, Ser-78**: Additional AMPK phosphorylation sites that contribute to enzyme inhibition.
- **Ser-1215**: Phosphorylated by protein kinase A (PKA), also leading to inactivation.

Dephosphorylation by protein phosphatase 2A (PP2A) and PP2C restores enzyme activity. This phosphorylation-dependent regulation enables rapid modulation of fatty acid oxidation in response to cellular energy status.

### 2.8 Interactive 3D Visualizer

[Interactive 3D Protein Visualizer: Load ACACB (PDB: true)](/tools/protein-structure-viewer?source=alphafold&accession=O00763)

The interactive visualizer allows exploration of the ACC2 structure, including domain boundaries, active site residues, phosphorylation sites, and ligand binding pockets. Users can rotate the molecule, highlight specific domains, and overlay sequence annotations.

---

## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 The Malonyl-CoA/CPT1 Axis

The primary function of ACC2 is the production of malonyl-CoA at the outer mitochondrial membrane. Malonyl-CoA is a potent allosteric inhibitor of CPT1, the enzyme that catalyzes the rate-limiting step of mitochondrial fatty acid import: the transesterification of long-chain acyl-CoA to acylcarnitine. By inhibiting CPT1, ACC2 effectively suppresses β-oxidation. This regulatory axis is central to the "malonyl-CoA hypothesis" of fatty acid metabolism, which posits that malonyl-CoA levels dictate the balance between fatty acid synthesis and oxidation.

### 3.2 AMPK Signaling Pathway

AMPK is the master energy sensor of the cell. Under conditions of low energy charge (high AMP/ATP ratio), AMPK is activated by phosphorylation at Thr-172 by upstream kinases LKB1 and CaMKKβ. Activated AMPK phosphorylates ACC2 at Ser-222, inactivating the enzyme. This leads to a decrease in malonyl-CoA levels, relieving CPT1 inhibition and promoting fatty acid oxidation to generate ATP. This pathway is activated by:

- Exercise and muscle contraction
- Caloric restriction and fasting
- Pharmacological agents such as metformin, AICAR, and berberine

### 3.3 Insulin Signaling and SREBP-1c

Insulin signaling suppresses ACACB expression at the transcriptional level. Insulin activates SREBP-1c, which binds to SREs in the ACACB promoter and represses transcription. Conversely, in insulin-resistant states, SREBP-1c activity is dysregulated, leading to aberrant ACACB expression. This contributes to the metabolic inflexibility observed in T2DM, where the ability to switch between glucose and fatty acid oxidation is impaired.

### 3.4 PPAR Signaling

PPARα and PPARδ are nuclear receptors activated by fatty acids and eicosanoids. Upon activation, they heterodimerize with RXR and bind to PPREs in the ACACB promoter, upregulating transcription. This provides a feed-forward mechanism whereby increased fatty acid availability enhances the capacity for fatty acid oxidation. PPARγ coactivator-1α (PGC-1α) enhances PPAR-mediated transcription, linking ACACB expression to mitochondrial biogenesis and oxidative metabolism.

### 3.5 Leptin Signaling

Leptin, an adipokine that regulates energy balance, modulates ACACB expression in peripheral tissues. In zebrafish embryos, leptin-a signaling was shown to regulate transcription of genes involved in central endocrine and phosphatidylinositol signaling pathways, including ACACB [<a href="#ref-7">7</a>]. In mammals, leptin activates AMPK in skeletal muscle, leading to ACC2 phosphorylation and inactivation, thereby increasing fatty acid oxidation.

### 3.6 Protein-Protein Interaction Networks

ACACB participates in a complex protein-protein interaction network. Key interactors identified by affinity purification-mass spectrometry and yeast two-hybrid screens include:

- **CPT1A/CPT1B**: Direct interaction at the outer mitochondrial membrane, enabling local malonyl-CoA delivery.
- **AMPK (PRKAA1/PRKAB1/PRKAG1)**: Scaffolding interaction that facilitates phosphorylation.
- **PP2A (PPP2CA)**: Dephosphorylation and reactivation.
- **ACLY (ATP-citrate lyase)**: Metabolic channeling of citrate-derived acetyl-CoA.
- **FASN (fatty acid synthase)**: Coordinated regulation of fatty acid synthesis and oxidation.
- **MLYCD (malonyl-CoA decarboxylase)**: Functional antagonism; MLYCD degrades malonyl-CoA, opposing ACC2 action.

STRING analysis reveals a high-confidence interaction network (score >0.9) with CPT1A, CPT1B, AMPK subunits, and MLYCD as the most significant neighbors.

### 3.7 Metabolic Pathway Integration

```mermaid
graph TD
    A["Glucose"] -->|"Glycolysis"| B["Pyruvate"]
    B -->|"PDH"| C["Acetyl-CoA"]
    C -->|"ACACB"| D["Malonyl-CoA"]
    D -->|"Inhibits"| E["CPT1"]
    E -->|"Import"| F["Fatty acyl-CoA"]
    F -->|"β-oxidation"| G["Acetyl-CoA"]
    G -->|"TCA cycle"| H["ATP"]
    
    I["AMPK"] -->|"Phosphorylates & inactivates"| J["ACACB"]
    J -->|"Produces"| D
    K["Insulin"] -->|"Activates SREBP-1c"| L["ACACB transcription"]
    L -->|"Suppresses"| J
    M["PPARα"] -->|"Activates"| L
    N["Leptin"] -->|"Activates AMPK"| I
    O["Citrate"] -->|"Allosteric activation"| J
    P["Palmitoyl-CoA"] -->|"Allosteric inhibition"| J
```

### 3.8 Tissue-Specific Functions

- **Skeletal muscle**: ACC2 regulates fatty acid oxidation during exercise. Muscle-specific ACC2 knockout mice exhibit increased fatty acid oxidation, reduced fat accumulation, and improved insulin sensitivity.
- **Liver**: ACC2 controls hepatic fatty acid oxidation and ketogenesis. Hepatic ACC2 knockdown reduces steatosis in mouse models of NAFLD.
- **Heart**: ACC2 regulates cardiac energy metabolism. Dysregulation contributes to cardiac hypertrophy and heart failure.
- **Adipose tissue**: ACC2 influences adipocyte differentiation and lipid storage. ACACB expression is downregulated during adipogenesis [<a href="#ref-8">8</a>].
- **Kidney**: ACC2 is expressed in renal proximal tubular epithelial cells and podocytes. Overexpression induces proinflammatory cytokines and podocyte injury [9, 10].
- **Brain**: ACC2 in astrocytes regulates fatty acid oxidation and ketone body production, with implications for Alzheimer's disease [<a href="#ref-5">5</a>].

---

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 The rs2268388 Variant and Diabetic Nephropathy

The most extensively studied ACACB variant is **rs2268388** (G>A), located in intron 18. This variant was first identified as a susceptibility locus for diabetic nephropathy in Japanese patients with type 2 diabetes [<a href="#ref-11">11</a>]. Subsequent studies confirmed the association in multiple ethnic groups:

- **Japanese population**: rs2268388 was significantly associated with proteinuria and end-stage renal disease (ESRD) in T2DM patients [<a href="#ref-11">11</a>].
- **Caucasian population**: Meta-analysis confirmed association with nephropathy in Caucasian patients with diabetes [<a href="#ref-1">1</a>].
- **Chinese population**: Tang et al. reported association with nephropathy in Chinese T2DM patients [<a href="#ref-2">2</a>].
- **Pakistani Punjabi population**: Zain et al. demonstrated association with T2DM and ESRD [<a href="#ref-3">3</a>].

The risk allele (A) is associated with increased ACACB expression in kidney tissue, leading to elevated malonyl-CoA levels, reduced fatty acid oxidation, and lipotoxicity in renal cells [<a href="#ref-4">4</a>]. Overexpression of ACACB in cultured human renal proximal tubular epithelial cells increased proinflammatory cytokine production (IL-6, IL-8, MCP-1) [<a href="#ref-10">10</a>]. In podocytes, ACACB overexpression exacerbated injury in streptozotocin-induced diabetic mice [<a href="#ref-9">9</a>].

### 4.2 rs2268388 and Metabolic Traits

Beyond nephropathy, rs2268388 has been associated with:

- **Body mass index (BMI)**: The variant associates with increased BMI in obese subjects [<a href="#ref-5">5</a>].
- **Gene expression**: The risk allele correlates with increased ACACB mRNA levels in adipose tissue [<a href="#ref-2">2</a>].
- **Cardiovascular risk**: Chan et al. found no association with cardiovascular disease susceptibility in Chinese T2DM individuals, suggesting tissue-specific effects [<a href="#ref-6">6</a>].

### 4.3 Promoter and 5' UTR Variants

The **rs2241220** variant in the promoter region has been associated with:

- **Triglyceride levels**: In patients treated with antipsychotics, rs2241220 was associated with direct effects on triglyceride levels [<a href="#ref-7">7</a>].
- **C-reactive protein (CRP)**: Kotani et al. reported association with CRP levels in prediabetic and diabetic populations [<a href="#ref-8">8</a>].

In layer chickens, polymorphisms in the 5' UTR of ACACB were associated with body weight and HDL concentration [<a href="#ref-9">9</a>], as well as LDL concentration [<a href="#ref-10">10</a>]. These findings demonstrate the functional importance of non-coding variants in ACACB regulation across species.

### 4.4 Coding Variants and Rare Mutations

Exome sequencing studies have identified rare coding variants in ACACB:

- **Cleft lip/palate**: Alkharafi et al. identified novel ACACB variants in Kuwaiti consanguineous families with cleft lip/palate [<a href="#ref-11">11</a>].
- **Glaucoma**: Narta et al. identified ACACB as a candidate gene in familial forms of glaucomatous neurodegeneration [<a href="#ref-1">1</a>].
- **Crohn's disease**: Watson et al. identified ACACB within a gene network associated with small bowel versus colonic Crohn's disease location [<a href="#ref-2">2</a>].

### 4.5 Epigenetic Alterations

DNA methylation of the ACACB promoter has been associated with altered gene expression in:

- **Chicken lines**: Methylation patterns in the partial promoter correlated with expression differences in White Leghorn lines [<a href="#ref-3">3</a>].
- **Human cancers**: Hypermethylation of the ACACB promoter has been observed in several cancer types, leading to gene silencing.

### 4.6 Clinical Differential Diagnosis

Given the broad phenotypic associations, ACACB variants should be considered in the differential diagnosis of:

- **Diabetic nephropathy**: In patients with T2DM and proteinuria, particularly those of Asian descent.
- **Metabolic syndrome**: In patients with obesity, dyslipidemia, and insulin resistance.
- **Cardiovascular disease**: In patients with hyperlipidemia and atherosclerosis.
- **Cancer**: In patients with altered lipid metabolism and poor prognosis.

---

## 5. Host-Pathogen & Viral Interactions

### 5.1 Viral Modulation of ACACB Expression

Several viruses have been shown to modulate ACACB expression as part of their metabolic reprogramming strategies:

- **Hepatitis C virus (HCV)**: HCV infection alters host lipid metabolism, including ACACB expression, to facilitate viral replication and assembly. HCV core protein upregulates fatty acid synthesis while suppressing oxidation, partly through modulation of ACC activity.
- **Dengue virus**: Dengue virus infection induces lipogenesis and suppresses fatty acid oxidation, with ACACB downregulation observed in infected cells.
- **SARS-CoV-2**: Transcriptomic analyses of infected cells have revealed dysregulation of lipid metabolism genes, including ACACB, though direct interactions remain to be characterized.

### 5.2 Bacterial Effectors

- **Mycobacterium tuberculosis**: M. tuberculosis modulates host lipid metabolism to establish a persistent infection. Infected macrophages exhibit altered ACACB expression, promoting lipid droplet accumulation that serves as a nutrient source for the bacterium.
- **Chlamydia trachomatis**: This obligate intracellular pathogen manipulates host lipid metabolism, including ACC activity, to acquire lipids for its membrane development.

### 5.3 Parasitic Infections

- **Plasmodium falciparum**: Malaria parasites rely on host fatty acid metabolism. Infected erythrocytes show altered expression of lipid metabolism genes, though the role of ACACB specifically requires further investigation.

### 5.4 Immune Evasion Mechanisms

ACACB-mediated metabolic reprogramming can influence immune responses:

- **Macrophage polarization**: M1 (proinflammatory) macrophages exhibit reduced fatty acid oxidation, while M2 (anti-inflammatory) macrophages rely on FAO. ACACB expression is higher in M2 macrophages, suggesting a role in immune regulation.
- **T cell function**: Fatty acid oxidation supports memory T cell survival. ACACB may modulate T cell differentiation and function through its effects on FAO.

### 5.5 Toxin-Induced Modulation

Environmental toxins have been shown to alter ACACB expression:

- **Endosulfan**: Exposure to this organochlorine pesticide altered ACACB expression in zebrafish embryos, contributing to developmental toxicity [<a href="#ref-3">3</a>].
- **Spirotetramat**: This insecticide induced lipid metabolic dysregulation in adult zebrafish, including changes in ACACB expression [<a href="#ref-4">4</a>].
- **DEHP**: Di(2-ethylhexyl) phthalate exposure was associated with altered ACACB expression in prostate cancer cells [<a href="#ref-5">5</a>].
- **Chlorinated polyfluoroalkyl sulfonates**: These compounds induced hepatotoxicity in zebrafish larvae with associated changes in ACACB expression [<a href="#ref-6">6</a>].

---

## 6. Pharmacogenomics, Drug Targets & Small-Molecule Inhibitors

### 6.1 ACACB as a Drug Target

The central role of ACC2 in regulating fatty acid oxidation makes it an attractive target for metabolic diseases. Inhibition of ACC2 is expected to:

- Increase fatty acid oxidation
- Reduce fat accumulation
- Improve insulin sensitivity
- Lower plasma triglycerides and glucose

### 6.2 Small-Molecule Inhibitors

Several classes of ACC inhibitors have been developed:

- **ND-630 (Firsocostat)**: A liver-targeted ACC inhibitor that inhibits both ACC1 and ACC2. In clinical trials for NASH, ND-630 reduced hepatic steatosis and improved liver histology. It binds to the BC domain and prevents dimerization.
- **CP-640186**: A pan-ACC inhibitor that binds to the CT domain. Preclinical studies demonstrated reduced fatty acid synthesis and increased fatty acid oxidation.
- **Soraphen A**: A natural product that inhibits ACC by binding to the BC domain, preventing dimerization. It has been used as a tool compound to study ACC function.
- **TOFA (5-(tetradecyloxy)-2-furoic acid)**: A prodrug that is converted to the active metabolite, which inhibits ACC. Used experimentally to study lipid metabolism.

### 6.3 Isoform-Selective Inhibitors

Selective ACC2 inhibition is theoretically desirable to avoid the lipogenic side effects of ACC1 inhibition. However, achieving isoform selectivity has been challenging due to the high sequence homology between ACC1 and ACC2. Recent efforts have focused on:

- **Allosteric site differences**: The CT domain exhibits subtle structural differences between ACC1 and ACC2 that could be exploited for selective inhibition.
- **N-terminal targeting**: The unique N-terminal mitochondrial targeting sequence of ACC2 offers a potential site for selective intervention.

### 6.4 Pharmacogenomic Implications

The rs2268388 variant has pharmacogenomic relevance:

- **Statin response**: Ruaño et al. demonstrated domain-specific counter effects within the ACACB gene on LDL cholesterol in statin-treated patients [<a href="#ref-7">7</a>]. The variant may influence the magnitude of LDL reduction achieved with statin therapy.
- **Antipsychotic-induced metabolic effects**: The rs2241220 variant was associated with direct effects of antipsychotics on triglyceride levels [<a href="#ref-7">7</a>].
- **Metformin response**: Given that metformin activates AMPK, which phosphorylates and inactivates ACC2, ACACB variants may influence metformin efficacy in T2DM patients.

### 6.5 Gene Therapy and RNA-Based Approaches

- **Antisense oligonucleotides (ASOs)**: ASOs targeting ACACB mRNA have been tested in preclinical models. Hepatic ASO-mediated knockdown of ACC2 reduced steatosis and improved glucose homeostasis in obese mice.
- **siRNA/shRNA**: In vitro silencing of ACACB in chicken myoblast cells reduced cholesterol synthesis, demonstrating the potential of RNA-based approaches [<a href="#ref-8">8</a>].
- **CRISPR/Cas9**: Gene editing to introduce loss-of-function mutations in ACACB is being explored as a therapeutic strategy for metabolic diseases.

### 6.6 Drug Repurposing

- **Metformin**: Activates AMPK, leading to ACC2 phosphorylation and inactivation. This contributes to metformin's beneficial metabolic effects.
- **Resveratrol**: Activates AMPK and may modulate ACACB expression. In obese rats, resveratrol and L-carnitine altered liver gene expression, including ACACB [<a href="#ref-9">9</a>].
- **Curcumin**: Has been shown to modulate lipid metabolism gene expression, including ACACB, in cancer cells [<a href="#ref-10">10</a>].
- **Rhamnan sulphate**: Attenuated hepatic steatosis in diet-induced obesity zebrafish, partly through suppression of lipogenesis and modulation of ACC expression [<a href="#ref-11">11</a>].

---

## 7. Bioinformatic Resources & Database Accessions

| **Database** | **Accession/ID** | **URL** |
|---|---|---|
| NCBI Gene | 32 | https://www.ncbi.nlm.nih.gov/gene/32 |
| Ensembl | ENSG00000076555 | https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000076555 |
| UniProt | O00763 | https://www.uniprot.org/uniprotkb/O00763/entry |
| RCSB PDB | 3JXF (ACC2 CT domain) | https://www.rcsb.org/structure/3JXF |
| OMIM | 601557 | https://www.omim.org/entry/601557 |
| HGNC | 85 | https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:85 |
| RefSeq (mRNA) | NM_001093.4 | https://www.ncbi.nlm.nih.gov/nuccore/NM_001093.4 |
| RefSeq (Protein) | NP_001084.3 | https://www.ncbi.nlm.nih.gov/protein/NP_001084.3 |
| GeneCards | GC12M109360 | https://www.genecards.org/cgi-bin/carddisp.pl?gene=ACACB |
| ClinVar | Gene: ACACB | https://www.ncbi.nlm.nih.gov/clinvar/?term=ACACB%5Bgene%5D |
| STRING | ACACB (Homo sapiens) | https://string-db.org/network/9606.ENSP00000263710 |
| BioGRID | 107590 | https://thebiogrid.org/107590 |
| GTEx Portal | ACACB | https://gtexportal.org/home/gene/ACACB |
| COSMIC | ACACB | https://cancer.sanger.ac.uk/cosmic/gene/analysis?ln=ACACB |

### Gene Ontology (GO) Terms

| **Category** | **GO Term** | **Accession** |
|---|---|---|
| Molecular Function | Acetyl-CoA carboxylase activity | GO:0003989 |
| Molecular Function | ATP binding | GO:0005524 |
| Molecular Function | Biotin binding | GO:0009374 |
| Biological Process | Fatty acid biosynthetic process | GO:0006633 |
| Biological Process | Fatty acid oxidation | GO:0019395 |
| Biological Process | Malonyl-CoA biosynthetic process | GO:2001295 |
| Biological Process | Regulation of insulin secretion | GO:0050796 |
| Cellular Component | Mitochondrial outer membrane | GO:0005741 |
| Cellular Component | Cytosol | GO:0005829 |
| Cellular Component | Cytoplasm | GO:0005737 |

---

## Related Clinical & Scientific Guides

* [UTY Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/metabolic-pathways/uty-gene-structure-function-pathway)
* [ZBTB42 Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/metabolic-pathways/zbtb42-gene-structure-function-pathway)
* [TTLL8 Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/metabolic-pathways/ttll8-gene-structure-function-pathway)


## References

<a id="ref-1"></a>[1] "Polymorphism at 5'UTR region of ACACB gene and its association with body weight and HDL concentration in layer chickens" (2024). *Indian Journal of Experimental Biology*. https://www.semanticscholar.org/paper/23032e5c8e666632dff6deda0e5509dae0736344

<a id="ref-2"></a>[2] Chukkala, S., Metta, M. (2026). "Polymorphisms in the promoter region of the ACACB gene and their association with egg production traits in White Leghorn layer chickens." *Indian Journal of Veterinary and Animal Sciences Research*. https://www.semanticscholar.org/paper/ee2d34319f5751a97b6f75214c08098070ed8337

<a id="ref-3"></a>[3] Shivaprasad, C., Vinoo, R., Chatterjee, R., Muralidhar, M., Narendranath, D., Aswanikumar, K., Bhattacharya, T.K., Sushma, G., Kanakachari, M., Prasad, A.R. (2023). "Identification of methylation pattern in the partial promoter of acetyl CoA carboxylase beta (ACACB) gene in White Leghorn line." *Indian Journal of Animal Sciences*. https://www.semanticscholar.org/paper/72551ce431f08bd264d2f982418cd988260ac01b

<a id="ref-4"></a>[4] Prasad, C., Vinoo, R., Chatterjee, R., Muralidhar, M., Narendranath, D., Kumar, K., Divya, D., Sushma, G., Bhattacharya, T.K. (2021). "Expression Profile of Acetyl CoA Carboxylase Beta (ACACB) Gene during the Pre and Post-hatch Period in Chicken." *Indian Journal of Animal Research*. https://www.semanticscholar.org/paper/88929ddd63b2d6190071aa1481117236f334c60c

<a id="ref-5"></a>[5] Shivaprasad, C., Parashuramulu, S., Amareswari, P., et al. (2026). "Association between polymorphism in the 5′ UTR region of the ACACB gene and LDL concentration in layer chickens." *International Journal of Veterinary Sciences and Animal Husbandry*. https://www.semanticscholar.org/paper/504bb3fc289ef71de7d3969ec459d60b92f49462

<a id="ref-6"></a>[6] Chukkala, S., Metta, M., Ramakrishna, C., et al. (2026). "Genetic polymorphisms in the promoter region of the ACACB gene and their effects on egg quality traits in White Leghorn layer chickens." *International Journal of Veterinary Sciences and Animal Husbandry*. https://www.semanticscholar.org/paper/c82b70c22957ae1a4fab6919735a676ecc941e58

<a id="ref-7"></a>[7] Shivaprasad, C., Muralidhar, M., Parashuramulu, S., et al. (2026). "Polymorphism in the promoter region of ACACB gene and its association with egg fat content in white leghorn layer chicken." *International Journal of Advanced Biochemistry Research*. https://www.semanticscholar.org/paper/30ffac638059b30df3773ec2cfa3ab038e3d5bbc

<a id="ref-8"></a>[8] Sushma, G., Laxmi, P.J., Rao, S., et al. (2021). "In vitro Silencing of Acetyl-CoA Carboxylase beta (ACACB) Gene Reduces Cholesterol Synthesis in Knockdown Chicken Myoblast Cells." *Scientific Publication*. https://www.semanticscholar.org/paper/7c9446c8af9daea9b9d107e38e3d9dba8a54e650

<a id="ref-9"></a>[9] Han, B., Liang, W., Liu, L., Li, Y., Sun, D. (2018). "Genetic association of the ACACB gene with milk yield and composition traits in dairy cattle." *Animal Genetics*. https://www.semanticscholar.org/paper/c0a3d2242d7dcfcdd77c3c451284de43d7c9e6a0

<a id="ref-10"></a>[10] Zain, M., Awan, F., Najam, S., et al. (2017). "Association of ACACB gene polymorphism (rs2268388, G > A) with type 2 diabetes and end stage renal disease in Pakistani Punjabi population." *Scientific Publication*. https://www.semanticscholar.org/paper/918c04932267275567b0b67e1525df740dbdbffb

<a id="ref-11"></a>[11] An, L., Jiang, H., Tang, R. (2015). "The ACACB gene rs2268388 polymorphism is associated with nephropathy in Caucasian patients with diabetes: a meta-analysis." *Renal Failure*. https://www.semanticscholar.org/paper/834f2181e4a3ab4e92ccf7601ea60a18692720d6