Structural Characterization of the Reaction and Substrate Specificity Mechanisms of Pathogenic Fungal Acetyl-CoA Synthetases.

Acetyl CoA synthetases (ACSs) are Acyl-CoA/NRPS/Luciferase (ANL) superfamily enzymes that couple acetate with CoA to generate acetyl CoA, a key component of central carbon metabolism in eukaryotes and prokaryotes. Normal mammalian cells are not dependent on ACSs, while tumor cells, fungi, and parasites rely on acetate as a precursor for acetyl CoA. Consequently, ACSs have emerged as a potential drug target. As part of a program to develop antifungal ACS inhibitors, we characterized fungal ACSs from five diverse human fungal pathogens using biochemical and structural studies. ACSs catalyze a two-step reaction involving adenylation of acetate followed by thioesterification with CoA. Our structural studies captured each step of these two half-reactions including the acetyl-adenylate intermediate of the first half-reaction in both the adenylation conformation and the thioesterification conformation and thus provide a detailed picture of the reaction mechanism. We also used a systematic series of increasingly larger alkyl adenosine esters as chemical probes to characterize the structural basis of the exquisite ACS specificity for acetate over larger carboxylic acid substrates. Consistent with previous biochemical and genetic data for other enzymes, structures of fungal ACSs with these probes bound show that a key tryptophan residue limits the size of the alkyl binding site and forces larger alkyl chains to adopt high energy conformers, disfavoring their efficient binding. Together, our analysis provides highly detailed structural models for both the reaction mechanism and substrate specificity that should be useful in designing selective inhibitors of eukaryotic ACSs as potential anticancer, antifungal, and antiparasitic drugs.

Targeting acetate metabolism: Achilles' nightmare.

Recent advances in our understanding of tumour heterogeneity alongside studies investigating altered metabolism within transformed tissue have identified metabolic pathways critical to cancer cell survival. Leveraging this information presents a promising new avenue for the generation of cancer-specific therapeutics and improved patient outcomes.

Targeting ACSS2 with a Transition-State Mimetic Inhibits Triple-Negative Breast Cancer Growth.

Acetyl-CoA is a vitally important and versatile metabolite used for many cellular processes including fatty acid synthesis, ATP production, and protein acetylation. Recent studies have shown that cancer cells upregulate acetyl-CoA synthetase 2 (ACSS2), an enzyme that converts acetate to acetyl-CoA, in response to stresses such as low nutrient availability and hypoxia. Stressed cancer cells use ACSS2 as a means to exploit acetate as an alternative nutrient source. Genetic depletion of ACSS2 in tumors inhibits the growth of a wide variety of cancers. However, there are no studies on the use of an ACSS2 inhibitor to block tumor growth. In this study, we synthesized a small-molecule inhibitor that acts as a transition-state mimetic to block ACSS2 activity in vitro and in vivo. Pharmacologic inhibition of ACSS2 as a single agent impaired breast tumor growth. Collectively, our findings suggest that targeting ACSS2 may be an effective therapeutic approach for the treatment of patients with breast cancer. SIGNIFICANCE: These findings suggest that targeting acetate metabolism through ACSS2 inhibitors has the potential to safely and effectively treat a wide range of patients with cancer.

Acetyl-CoA Synthetase 2 Promotes Cell Migration and Invasion of Renal Cell Carcinoma by Upregulating Lysosomal-Associated Membrane Protein 1 Expression.

BACKGROUND/AIMS: Reprogramming energy metabolism is an emerging hallmark of many cancers, and this alteration is especially evident in renal cell carcinomas (RCCs). However, few studies have been conducted on lipid metabolism. This study investigated the function and mechanism of lipid metabolism-related acetyl-CoA synthetase 2 (ACSS2) in RCC development, cell migration and invasion. METHODS: Quantitative real-time PCR (qRT-PCR) was used to determine the expression of ACSS2 in cancer tissue and adjacent tissue. The inhibition of ACSS2 expression was achieved by RNA interference, which was confirmed by qRT-PCR and Western blotting. Cell proliferation and apoptosis were detected by a CCK8 assay and a flow cytometry analysis, respectively. Cell migration and invasion were determined by the scratch and transwell assays. Following the knockdown of ACSS2 expression, the expression of the autophagy-related factor LAMP1 was measured by qRT-PCR and Western blotting. RESULTS: Compared to adjacent tissues, ACSS2 expression was upregulated in RCC cancer tissues and positively correlated with metastasis. Inhibition of ACSS2 had no effect on RCC cell proliferation or apoptosis. However, decreased ACSS2 expression was found to inhibit RCC cell migration and invasion. ACSS2 was determined to promote the expression of LAMP1, which can also promote cell migration. This pathway may be considered a potential mechanism through which ACSS2 participates in RCC development. CONCLUSION: These data suggest that ACSS2 is an important factor for promoting RCC development and is essential for cell migration and invasion, which it promotes by increasing the expression of LAMP1. Taken together, these findings reveal a potential target for the diagnosis and treatment of RCC.

Acetate Recapturing by Nuclear Acetyl-CoA Synthetase 2 Prevents Loss of Histone Acetylation during Oxygen and Serum Limitation.

Acetyl-CoA is a key metabolic intermediate with an important role in transcriptional regulation. The nuclear-cytosolic acetyl-CoA synthetase 2 (ACSS2) was found to sustain the growth of hypoxic tumor cells. It generates acetyl-CoA from acetate, but exactly which pathways it supports is not fully understood. Here, quantitative analysis of acetate metabolism reveals that ACSS2 fulfills distinct functions depending on its cellular location. Exogenous acetate uptake is controlled by expression of both ACSS2 and the mitochondrial ACSS1, and ACSS2 supports lipogenesis. The mitochondrial and lipogenic demand for two-carbon acetyl units considerably exceeds the uptake of exogenous acetate, leaving it to only sparingly contribute to histone acetylation. Surprisingly, oxygen and serum limitation increase nuclear localization of ACSS2. We find that nuclear ACSS2 recaptures acetate released from histone deacetylation for recycling by histone acetyltransferases. Our work provides evidence for limited equilibration between nuclear and cytosolic acetyl-CoA and demonstrates that ACSS2 retains acetate to maintain histone acetylation.

Biochemical and kinetic characterization of the recombinant ADP-forming acetyl coenzyme A synthetase from the amitochondriate protozoan Entamoeba histolytica.

Entamoeba histolytica, an amitochondriate protozoan parasite that relies on glycolysis as a key pathway for ATP generation, has developed a unique extended PPi-dependent glycolytic pathway in which ADP-forming acetyl-coenzyme A (CoA) synthetase (ACD; acetate:CoA ligase [ADP-forming]; EC 6.2.1.13) converts acetyl-CoA to acetate to produce additional ATP and recycle CoA. We characterized the recombinant E. histolytica ACD and found that the enzyme is bidirectional, allowing it to potentially play a role in ATP production or in utilization of acetate. In the acetate-forming direction, acetyl-CoA was the preferred substrate and propionyl-CoA was used with lower efficiency. In the acetyl-CoA-forming direction, acetate was the preferred substrate, with a lower efficiency observed with propionate. The enzyme can utilize both ADP/ATP and GDP/GTP in the respective directions of the reaction. ATP and PPi were found to inhibit the acetate-forming direction of the reaction, with 50% inhibitory concentrations of 0.81 ± 0.17 mM (mean ± standard deviation) and 0.75 ± 0.20 mM, respectively, which are both in the range of their physiological concentrations. ATP and PPi displayed mixed inhibition versus each of the three substrates, acetyl-CoA, ADP, and phosphate. This is the first example of regulation of ACD enzymatic activity, and possible roles for this regulation are discussed.

Inhibition effect of isopropanol on acetyl-CoA synthetase expression level of acetoclastic methanogen, Methanosaeta concilii.

Isopropanol is a widely found solvent in industrial wastewaters, which have commonly been treated using anaerobic systems. In this study, inhibitory effect of isopropanol on the key microbial group in anaerobic bioreactors, acetoclastic methanogens, was investigated. Anaerobic sludges in serum bottles were repeatedly fed with acetate and isopropanol; and quantitative real-time PCR was used for determining effect of isopropanol on the expression level of a key enzyme in acetoclastic methane production, acetyl-CoA synthetase of Methanosaeta concilii. Active Methanosaeta spp. cells were also quantified using Fluorescent in situ hybridization (FISH). Transcript abundance of acetyl-CoA synthetase was 1.23±0.62×10(6) mRNAs/mL in the uninhibited reactors with 222 mL cumulative methane production. First exposure to isopropanol resulted in 71.2%, 84.7%, 89.2% and 94.6% decrease in mRNA level and 35.0%, 65.0%, 91.5% and 100.0% reduction in methane production for isopropanol concentrations of 0.1 M, 0.5 M, 1.0 M and 2.0 M, respectively. Repeated exposures resulted in higher inhibitions; and at the end of test, fluorescent intensities of active Methanosaeta cells were significantly decreased due to isopropanol. The overall results indicated that isopropanol has an inhibitory effect on acetoclastic methanogenesis; and the inhibition can be detected by monitoring level of acetyl-CoA transcripts and rRNA level.

Connection of propionyl-CoA metabolism to polyketide biosynthesis in Aspergillus nidulans.

Propionyl-CoA is an intermediate metabolite produced through a variety of pathways including thioesterification of propionate and catabolism of odd chain fatty acids and select amino acids. Previously, we found that disruption of the methylcitrate synthase gene, mcsA, which blocks propionyl-CoA utilization, as well as growth on propionate impaired production of several polyketides-molecules typically derived from acetyl-CoA and malonyl-CoA-including sterigmatocystin (ST), a potent carcinogen, and the conidiospore pigment. Here we describe three lines of evidence that demonstrate that excessive propionyl-CoA levels in the cell can inhibit polyketide synthesis. First, inactivation of a putative propionyl-CoA synthase, PcsA, which converts propionate to propionyl-CoA, restored polyketide production and reduced cellular propionyl-CoA content in a DeltamcsA background. Second, inactivation of the acetyl-CoA synthase, FacA, which is also involved in propionate utilization, restored polyketide production in the DeltamcsA background. Third, fungal growth on several compounds (e.g., heptadecanoic acid, isoleucine, and methionine) whose catabolism includes the formation of propionyl-CoA, were found to inhibit ST and conidiospore pigment production. These results demonstrate that excessive propionyl-CoA levels in the cell can inhibit polyketide synthesis.

Triglyceride depletion in THP-1 cells alters cholesteryl ester physical state and cholesterol efflux.

To study macrophage lipid droplet composition and the effects of TG on cholesteryl ester (CE) physical state, hydrolysis, and cholesterol efflux, a technique was developed to remove the majority of accumulated TG with minimal effect on CE content. THP-1 macrophages were incubated with acetylated LDL, and the accumulated TG was depleted by incubation with the acyl-CoA synthetase inhibitor triacsin D in the presence of albumin. Before TG removal, all cellular lipid droplets were isotropic as determined by polarizing light microscopy. When the TG concentration was reduced, anisotropic lipid droplets were visible, indicating a change in physical state, and suggesting that TG and CE originally accumulated in mixed lipid droplets. This change in physical state of lipid droplets was associated with slower rates of CE hydrolysis and cholesterol efflux. Although lipid droplets within the same cell had a similar physical state after TG depletion, there was considerable variability among cells in the physical state of their lipid droplets. In conclusion, THP-1 macrophages store accumulated CE and TG in mixed droplets, and the proportion of CE to TG varies among cells. Reducing accumulated TG altered CE physical state, which in turn affected hydrolysis of CE and cholesterol efflux.

Isolation and characterization of acetyl-coenzyme A synthetase from Methanothrix soehngenii.

In Methanothrix soehngenii, acetate is activated to acetyl-coenzyme A (acetyl-CoA) by an acetyl-CoA synthetase. Cell extracts contained high activities of adenylate kinase and pyrophosphatase, but no activities of a pyrophosphate:AMP and pyrophosphate:ADP phosphotransferase, indicating that the activation of 1 acetate in Methanothrix requires 2 ATP. Acetyl-CoA synthetase was purified 22-fold in four steps to apparent homogeneity. The native molecular mass of the enzyme from M. soehngenii estimated by gel filtration was 148 kilodaltons (kDa). The enzyme was composed of two subunits with a molecular mass of 73 kDa in an alpha 2 oligomeric structure. The acetyl-CoA synthetase constituted up to 4% of the soluble cell protein. At the optimum pH of 8.5, the Vmax was 55 mumol of acetyl-CoA formed per min per mg of protein. Analysis of enzyme kinetic properties revealed a Km of 0.86 mM for acetate and 48 microM for coenzyme A. With varying amounts of ATP, weak sigmoidal kinetic was observed. The Hill plot gave a slope of 1.58 +/- 0.12, suggesting two interacting substrate sites for the ATP. The kinetic properties of the acetyl-CoA synthetase can explain the high affinity for acetate of Methanothrix soehngenii.

Stable analogs of acyl adenylates. Inhibition of acetyl- and acyl-CoA synthetase by adenosine 5'-alkylphosphates.

Adenosine 5'-alkylphosphates are potent inhibitors of acetyl- and acyl-CoA synthetase. In each case, the most effective inhibitor in the series is homologous with the tightly bound acyl adenylate intermediate. Adenosine 5'-ethylphosphate (Ki = 33 nM) is 88-fold more potent than adenosine 5'-methylphosphate (Ki = 2900 nM) as a competitive inhibitor of acetyl-CoA synthetase; the contribution of a single carbon to the observed binding energy (-11 kJ/mol) is much larger than is typically observed.

[Organophosphate analogs of biologically active compounds. XIV. Halophosphonate analogs of ATP as acetyl CoA carboxylase inhibitors]. / Fosfororganicheskie analogi biologicheski aktivnykh soedinenii. XIV. Galoidfosfonatnye analogi ATP kak ingibitory Ac CoA-karboksilazy.

Halophosphonate ATP analogues pp[CHBr]pA and p[CHBr]ppA synthesised from bromomethylenebisphosphonate and adenosine derivatives, proved to be effective competitive inhibitors of Ac-CoA-carboxylase (CE 6.4.1.2) from rat liver (Ki = 0,2 mM). The inhibitory effects of both analogues were reversible and higher than those of some other ATP analogues. Another enzyme, Ac-CoA-synthetase (CE 6.2.1.1), with a different mode of ATP-cleavage showed wider specificity to ATP-analogues than Ac-CoA-carboxylase.

Regulation of acetyl-CoA synthetase of Saccharomyces cerevisiae.

Acetyl-coenzyme A synthetase (EC 6.2.1.1) activity of Saccharomyces cerevisiae was determined by a radioactive assay procedure. The activity in vitro was inhibited significantly by NADPH, NADH, or AMP and to a lesser extent by NADP, NAD, or ADP. Glutamic acid and alpha-ketoglutaric acid were not inhibitory. The enzyme level was repressed when the cells were grown in a complex nutrient medium as opposed to the minimal medium. However, a glutamic acid auxotroph glul, when grown in excess glutamic acid, demonstrated a fivefold increase of acetyl-CoA synthetase.