The human ACC2 CT-domain C-terminus is required for full functionality and has a novel twist

Acetyl-CoA Carboxylases and Diseases

Acetyl-CoA carboxylases (ACCs) are enzymes that catalyze the carboxylation of acetyl-CoA to produce malonyl-CoA. In mammals, ACC1 and ACC2 are two members of ACCs. ACC1 localizes in the cytosol and acts as the first and rate-limiting enzyme in the de novo fatty acid synthesis pathway. ACC2 localizes on the outer membrane of mitochondria and produces malonyl-CoA to regulate the activity of carnitine palmitoyltransferase 1 (CPT1) that involves in the β-oxidation of fatty acid. Fatty acid synthesis is central in a myriad of physiological and pathological conditions. ACC1 is the major member of ACCs in mammalian, mountains of documents record the roles of ACC1 in various diseases, such as cancer, diabetes, obesity. Besides, acetyl-CoA and malonyl-CoA are cofactors in protein acetylation and malonylation, respectively, so that the manipulation of acetyl-CoA and malonyl-CoA by ACC1 can also markedly influence the profile of protein post-translational modifications, resulting in alternated biological processes in mammalian cells. In the review, we summarize our understandings of ACCs, including their structural features, regulatory mechanisms, and roles in diseases. ACC1 has emerged as a promising target for diseases treatment, so that the specific inhibitors of ACC1 for diseases treatment are also discussed.

Synthesis and biological evaluation of 4-phenoxy-phenyl isoxazoles as novel acetyl-CoA carboxylase inhibitors

Acetyl-CoA carboxylase (ACC) is a crucial enzyme in fatty acid metabolism, which plays a major role in the occurrence and development of certain tumours. Herein, one potential ACC inhibitor (6a) was identified through high-throughput virtual screening (HTVS), and a series of 4-phenoxy-phenyl isoxazoles were synthesised for structure-activity relationship (SAR) studies. Among these compounds, 6g exhibited the most potent ACC inhibitory activity (IC₅₀=99.8 nM), which was comparable to that of CP-640186. Moreover, the antiproliferation assay revealed that compound 6l exhibited the strongest cytotoxicity, with IC₅₀ values of 0.22 µM (A549), 0.26 µM (HepG2), and 0.21 µM (MDA-MB-231), respectively. The preliminary mechanistic studies on 6g and 6l suggested that the compounds decreased the malonyl-CoA levels, arrested the cell cycle at the G0/G1 phase, and induced apoptosis in MDA-MB-231 cells. Overall, these results indicated that the 4-phenoxy-phenyl isoxazoles are potential for further study in cancer therapeutics as ACC inhibitors.

Recent development in acetyl-CoA carboxylase inhibitors and their potential as novel drugs

Acetyl-CoA carboxylase (ACC), a critical enzyme in the regulation of fatty acid synthesis and metabolism, has emerged as an attractive target for a plethora of emerging diseases, such as diabetes mellitus, nonalcoholic fatty liver disease, cancer, bacterial infections and so on. With decades of efforts in medicinal chemistry, significant progress has been made toward the design and discovery of a considerable number of inhibitors of this enzyme. In this review, we not only clarify the role of ACC in emerging diseases, but also summarize recent developments of potent ACC inhibitors and discuss their molecular mechanisms of action and potentials as novel drugs as well as future perspectives toward the design and discovery of novel ACC inhibitors.

Striking Diversity in Holoenzyme Architecture and Extensive Conformational Variability in Biotin-Dependent Carboxylases

Biotin-dependent carboxylases are widely distributed in nature and have central roles in the metabolism of fatty acids, amino acids, carbohydrates, and other compounds. The last decade has seen the accumulation of structural information on most of these large holoenzymes, including the 500-kDa dimeric yeast acetyl-CoA carboxylase, the 750-kDa α₆β₆ dodecameric bacterial propionyl-CoA carboxylase, 3-methylcrotonyl-CoA carboxylase, and geranyl-CoA carboxylase, the 720-kDa hexameric bacterial long-chain acyl-CoA carboxylase, the 500-kDa tetrameric bacterial single-chain pyruvate carboxylase, the 370-kDa α₂β₄ bacterial two-subunit pyruvate carboxylase, and the 130-kDa monomeric eukaryotic urea carboxylase. A common theme that has emerged from these studies is the dramatic structural flexibility of these holoenzymes despite their strong overall sequence conservation, evidenced both by the extensive diversity in the architectures of the holoenzymes and by the extensive conformational variability of their domains and subunits. This structural flexibility is crucial for the function and regulation of these enzymes and identifying compounds that can interfere with it represents an attractive approach for developing novel modulators and drugs. The extensive diversity observed in the structures so far and its biochemical and functional implications will be the focus of this review.

Synthesis, Biological Evaluation and Molecular Docking Studies of Piperidinylpiperidines and Spirochromanones Possessing Quinoline Moieties as Acetyl-CoA Carboxylase Inhibitors

Acetyl-coenzyme A carboxylases (ACCs) play critical roles in the regulation of fatty acid metabolism and have been targeted for the development of drugs against obesity, diabetes and other metabolic diseases. Two series of compounds possessing quinoline moieties were designed, synthesized and evaluated for their potential to inhibit acetyl-CoA carboxylases. Most compounds showed moderate to good ACC inhibitory activities and compound 7a possessed the most potent biological activities against ACC1 and ACC2, with IC50 values of 189 nM and 172 nM, respectively, comparable to the positive control. Docking simulation was performed to position compound 7a into the active site of ACC to determine a probable binding model.

Structure of amylase-binding protein A of Streptococcus gordonii: a potential receptor for human salivary α-amylase enzyme

Amylase-binding protein A (AbpA) of a number of oral streptococci is essential for the colonization of the dental pellicle. We have determined the solution structure of residues 24-195 of AbpA of Streptococcus gordonii and show a well-defined core of five helices in the region of 45-115 and 135-145. (13) Cα/β chemical shift and heteronuclear (15) N-{(1) H} NOE data are consistent with this fold and that the remainder of the protein is unstructured. The structure will inform future molecular experiments in defining the mechanism of human salivary α-amylase binding and biofilm formation by streptococci.

Recent advances in the development of acetyl-CoA carboxylase (ACC) inhibitors for the treatment of metabolic disease

The development of acetyl-CoA carboxylase (ACC) inhibitors for the treatment of metabolic disease has been pursued by the pharmaceutical industry for some time. A number of recent disclosures describing potent ACC inhibitors have been reported by multiple research groups. Unlike many prior publications in this area, more recent publications contain a significant amount of in vivo efficacy data generated by long-term experiments in rodent models of metabolic disease. Additionally, one compound has been advanced to human clinical studies. The results from these studies should allow researchers to better gauge the potential utility of ACC inhibition for the treatment of human disease.

The enzymes of biotin dependent CO₂ metabolism: what structures reveal about their reaction mechanisms

Biotin is the major cofactor involved in carbon dioxide metabolism. Indeed, biotin-dependent enzymes are ubiquitous in nature and are involved in a myriad of metabolic processes including fatty acid synthesis and gluconeogenesis. The cofactor, itself, is composed of a ureido ring, a tetrahydrothiophene ring, and a valeric acid side chain. It is the ureido ring that functions as the CO₂ carrier. A complete understanding of biotin-dependent enzymes is critically important for translational research in light of the fact that some of these enzymes serve as targets for anti-obesity agents, antibiotics, and herbicides. Prior to 1990, however, there was a dearth of information regarding the molecular architectures of biotin-dependent enzymes. In recent years there has been an explosion in the number of three-dimensional structures reported for these proteins. Here we review our current understanding of the structures and functions of biotin-dependent enzymes. In addition, we provide a critical analysis of what these structures have and have not revealed about biotin-dependent catalysis.

Structure and function of biotin-dependent carboxylases

Biotin-dependent carboxylases include acetyl-CoA carboxylase (ACC), propionyl-CoA carboxylase (PCC), 3-methylcrotonyl-CoA carboxylase (MCC), geranyl-CoA carboxylase, pyruvate carboxylase (PC), and urea carboxylase (UC). They contain biotin carboxylase (BC), carboxyltransferase (CT), and biotin-carboxyl carrier protein components. These enzymes are widely distributed in nature and have important functions in fatty acid metabolism, amino acid metabolism, carbohydrate metabolism, polyketide biosynthesis, urea utilization, and other cellular processes. ACCs are also attractive targets for drug discovery against type 2 diabetes, obesity, cancer, microbial infections, and other diseases, and the plastid ACC of grasses is the target of action of three classes of commercial herbicides. Deficiencies in the activities of PCC, MCC, or PC are linked to serious diseases in humans. Our understanding of these enzymes has been greatly enhanced over the past few years by the crystal structures of the holoenzymes of PCC, MCC, PC, and UC. The structures reveal unanticipated features in the architectures of the holoenzymes, including the presence of previously unrecognized domains, and provide a molecular basis for understanding their catalytic mechanism as well as the large collection of disease-causing mutations in PCC, MCC, and PC. This review will summarize the recent advances in our knowledge on the structure and function of these important metabolic enzymes.

Resistance to spiromesifen in Trialeurodes vaporariorum is associated with a single amino acid replacement in its target enzyme acetyl-coenzyme A carboxylase

Spiromesifen is a novel insecticide and is classed as a tetronic acid derivative. It targets the insects' acetyl-coenzyme A carboxylase (ACCase) enzyme, causing a reduction in lipid biosynthesis. At the time of this publication, there are no reports of resistance to this class of insecticides in insects although resistance has been observed in several mite species. The greenhouse whitefly Trialeurodes vaporariorum (Westwood) is a serious pest of protected vegetable and ornamental crops in temperate regions of the world and spiromesifen is widely used in its control. Mortality rates of UK and European populations of T. vaporariorum to spiromesifen were calculated and up to 26-fold resistance was found. We therefore sought to examine the molecular mechanism underlying spiromesifen resistance in this important pest. Pre-treatment with piperonyl butoxide did not synergize spiromesifen, suggesting a target-site resistance mechanism. The full length ACCase gene was sequenced for a range of T. vaporariorum strains and a strong association was found between spiromesifen resistance and a glutamic acid substitution with lysine in position 645 (E645K) of this gene. A TaqMan allelic discrimination assay confirmed these findings. Although this resistance is not considered sufficient to compromise the field performance of spiromesifen, this association of E645K with resistance is the first report of a potential target site mechanism affecting an ACCase inhibitor in an arthropod species.

Structure, function and selective inhibition of bacterial acetyl-coa carboxylase

Acetyl-CoA carboxylase (ACC) catalyses the first committed step in fatty acid biosynthesis: a metabolic pathway required for several important biological processes including the synthesis and maintenance of cellular membranes. ACC employs a covalently attached biotin moiety to bind a carboxyl anion and then transfer it to acetyl-CoA, yielding malonyl-CoA. These activities occur at two different subsites: the biotin carboxylase (BC) and carboxyltransferase (CT). Structural biology, together with small molecule inhibitor studies, has provided new insights into the molecular mechanisms that govern ACC catalysis, specifically the BC and CT subunits. Here, we review these recent findings and highlight key differences between the bacterial and eukaryotic isozymes with a view to establish those features that provide an opportunity for selective inhibition. Especially important are examples of highly selective small molecule inhibitors capable of differentiating between ACCs from different phyla. The implications for early stage antibiotic discovery projects, stemming from these studies, are discussed.

Structure-guided inhibitor design for human acetyl-coenzyme A carboxylase by interspecies active site conversion

Inhibition of acetyl-CoA carboxylases (ACCs), a crucial enzyme for fatty acid metabolism, has been shown to promote fatty acid oxidation and reduce body fat in animal models. Therefore, ACCs are attractive targets for structure-based inhibitor design, particularly the carboxyltransferase (CT) domain, which is the primary site for inhibitor interaction. We have cloned, expressed, and purified the CT domain of human ACC2 using baculovirus-mediated insect cell expression system. However, attempts to crystallize the human ACC2 CT domain have not been successful in our hands. Hence, we have been using the available crystal structure of yeast CT domain to design human ACC inhibitors. Unfortunately, as the selectivity of the lead series has increased against the full-length human enzyme, the potency against the yeast enzyme has decreased significantly. This loss of potency against the yeast enzyme correlated with a complete lack of binding of the human-specific compounds to crystals of the yeast CT domain. Here, we address this problem by converting nine key active site residues of the yeast CT domain to the corresponding human residues. The resulting humanized yeast ACC-CT (yCT-H9) protein exhibits biochemical and biophysical properties closer to the human CT domain and binding to human specific compounds. We report high resolution crystal structures of yCT-H9 complexed with inhibitors that show a preference for the human CT domain. These structures offer insights that explain the species selectivity of ACC inhibitors and may guide future drug design programs.

Design of small molecule inhibitors of acetyl-CoA carboxylase 1 and 2 showing reduction of hepatic malonyl-CoA levels in vivo in obese Zucker rats

Inhibition of acetyl-CoA carboxylases has the potential for modulating long chain fatty acid biosynthesis and mitochondrial fatty acid oxidation. Hybridization of weak inhibitors of ACC2 provided a novel, moderately potent but lipophilic series. Optimization led to compounds 33 and 37, which exhibit potent inhibition of human ACC2, 10-fold selectivity over inhibition of human ACC1, good physical and in vitro ADME properties and good bioavailability. X-ray crystallography has shown this series binding in the CT-domain of ACC2 and revealed two key hydrogen bonding interactions. Both 33 and 37 lower levels of hepatic malonyl-CoA in vivo in obese Zucker rats.

Crystal structure of Spot 14, a modulator of fatty acid synthesis

Spot 14 (S14) is a protein that is abundantly expressed in lipogenic tissues and is regulated in a manner similar to other enzymes involved in fatty acid synthesis. Deletion of S14 in mice decreased lipid synthesis in lactating mammary tissue, but the mechanism of S14's action is unknown. Here we present the crystal structure of S14 to 2.65 Å and biochemical data showing that S14 can form heterodimers with MIG12. MIG12 modulates fatty acid synthesis by inducing the polymerization and activity of acetyl-CoA carboxylase, the first committed enzymatic reaction in the fatty acid synthesis pathway. Coexpression of S14 and MIG12 leads to heterodimers and reduced acetyl-CoA carboxylase polymerization and activity. The structure of S14 suggests a mechanism whereby heterodimer formation with MIG12 attenuates the ability of MIG12 to activate ACC.

A different mechanism for the inhibition of the carboxyltransferase domain of acetyl-coenzyme A carboxylase by tepraloxydim

Acetyl-CoA carboxylases (ACCs) are crucial metabolic enzymes and are attractive targets for drug discovery. Haloxyfop and tepraloxydim belong to two distinct classes of commercial herbicides and kill sensitive plants by inhibiting the carboxyltransferase (CT) activity of ACC. Our earlier structural studies showed that haloxyfop is bound near the active site of the CT domain, at the interface of its dimer, and a large conformational change in the dimer interface is required for haloxyfop binding. We report here the crystal structure at 2.3 A resolution of the CT domain of yeast ACC in complex with tepraloxydim. The compound has a different mechanism of inhibiting the CT activity compared to haloxyfop, as well as the mammalian ACC inhibitor CP-640186. Tepraloxydim probes a different region of the dimer interface and requires only small but important conformational changes in the enzyme, in contrast to haloxyfop. The binding mode of tepraloxydim explains the structure-activity relationship of these inhibitors, and provides a molecular basis for their distinct sensitivity to some of the resistance mutations, as compared to haloxyfop. Despite the chemical diversity between haloxyfop and tepraloxydim, the compounds do share two binding interactions to the enzyme, which may be important anchoring points for the development of ACC inhibitors.