Abstract
ATP citrate lyase (ACL) is a cytosolic enzyme that catalyzes the synthesis of acetyl-CoA and oxaloacetate using citrate, CoA, and ATP as substrates and Mg(2+) as a necessary cofactor. The ACL-dependent synthesis of acetyl-CoA is thought to be an essential step for the de novo synthesis of fatty acids and cholesterol. For this reason, inhibition of ACL has been pursued as a strategy to treat dyslipidemia and obesity. Traditionally, ACL enzyme activity is measured indirectly by coupling to enzymes such as malate dehydrogenase or chloramphenicol acetyl transferase. In this report, however, we describe a novel procedure to directly measure ACL enzyme activity. We first identified a convenient method to specifically detect [(14)C]acetyl-CoA without detecting [(14)C]citrate by MicroScint-O. Using this detection system, we devised a simple, direct, and homogeneous ACL assay in 384-well plate format that is suitable for high-throughput screening. The current assay consists of 1) incubation of ACL enzyme with [(14)C]citrate and other substrates/cofactors CoA, ATP, and Mg(2+), 2) EDTA quench, 3) addition of MicroScint-O, the agent that specifically detects product [(14)C]acetyl-CoA, and 4) detection of signal by TopCount. This unique ACL assay may provide more efficient identification of new ACL inhibitors and allow detailed mechanistic characterization of ACL/inhibitor interactions.
Highlights
ATP citrate lyase (ACL) is a cytosolic enzyme that catalyzes the synthesis of acetyl-CoA and oxaloacetate using citrate, CoA, and ATP as substrates and Mg2+ as a necessary cofactor
Selective detection of [14C]acetyl CoA by MicroScint-O Equation 1 illustrates the biochemical reactions catalyzed by ACL that are conducted in the current study
Further testing demonstrated that the linearity of [14C]acetyl CoA signal can be extended to at least 1 mM, indicating that MicroScint-O-based detection for [14C]acetyl CoA signal is a robust system with a wide dynamic range
Summary
ATP citrate lyase (ACL) is a cytosolic enzyme that catalyzes the synthesis of acetyl-CoA and oxaloacetate using citrate, CoA, and ATP as substrates and Mg2+ as a necessary cofactor. The current assay consists of 1) incubation of ACL enzyme with [14C]citrate and other substrates/cofactors CoA, ATP, and Mg2+, 2) EDTA quench, 3) addition of MicroScint-O, the agent that detects product [14C]acetyl-CoA, and 4) detection of signal by TopCount. Chronic administration of Compound 9 (or BMS-303141), the leading inhibitor in this class, in high-fat–fed mice reduced weight gain and lowered plasma cholesterol, triglycerides, and glucose. All these data are consistent with the hypothesis that ACL might be an attractive target for the treatment of metabolic disorders, including obesity and dyslipidemia
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