Carboxylesterases are enzymes in the a/b hydrolase fold and catalyze the hydrolysis of carboxyl esters via the addition of water as shown below. The a/b hydrolase fold also includes phosphotriesterases (such as paraoxonase), cholinesterases, epoxide hydrolases and lipases as well as a number of other enzymes. These enzymes are all defined by an eight-stranded mostly parallel a/b structure and a characteristic plastic nature of the protein fold that allows for large variations in domain size. In addition to this common structural framework, carboxylesterases share a 2-step serine hydrolase mechanism and active site.

Carboxylesterases are found in a number of tissues including liver, kidney, small intestine, heart, muscle, lung, brain, testis, nasal and respiratory tissues, adipose tissue, leukocytes, and the blood. However, their expression and activity is organism dependent, with levels and activities varying widely. Polymorphisms have been reported, and in particular 15 single nucleotide polymorphisms (SNPs) were identified in one carboxylesterasealone (CaE2 or CES2). The esterase family is still growing as more esterases are identified and the ESTHER database currently contains 5,237 nucleotide sequences for genes that encode esterases, of which 318 are carboxylesterases. 

Interest in this class of enzymes has increased due to their role in the metabolism of many agrochemicals and pharmaceuticals, as well as their role in endogenous metabolism. Carboxylesterases hydrolyze a battery of drugs, including beta-blockers, statins, cocaine, aspirin and the anti-tumorgenic agent CPT-11. In addition, carboxylesterase activity is necessary to activate the pro-drug oseltamivir, the main anti-influenza agent recommended by the World Health Organization, to its active metabolite. Carboxylesterases are key enzymes in the detoxification of pyrethroid, organophosphate, and carbamate insecticides. The study of these enzymes is a rapidly evolving field of increasing interest due to their clinical and environmental significance. However, the endogenous role of the enzyme remains unknown and is subsequently an important area of investigation.

Our research focuses on understanding the mechanistic biochemistry behind carboxylesterase inhibition and substrate hydrolysis. Given the role of esterases in metabolism, it is important to understand their structure and activity in order to predict the hydrolysis of new drugs or agrochemicals and prevent adverse interactions. We approach this work from the standpoint of synthetic organic and analytical chemistry in combination with computer modeling. One of the most potent inhibitors of carboxylesterases found to date are a group of compounds termed trifluoromethyl ketones (TFKs), consisting of a trifluoromethyl group alpha to a ketone. The trifluoroacyl moiety is efficient at inhibiting enzymes whose mechanisms involve a nucleophilic attack by a catalytic serine residue. Several important enzymes have been inhibited by compounds containing this moiety including acetylcholinesterase and HIV-1 protease, as well as carboxylesterase. We have synthesized new members of this class of compounds and developed predictive models of the inhibitory mechanism using ab initio calculations and quantitative structure activity relationships (QSAR). These studies show a focused application of organic and analytical chemistry to understand pharmaceutical and agrochemical metabolism, with the results augmented through the use of computational chemistry.

Current work involves examining the role of carboxylesterases in lipid homeostasis with focus on a number of enzymes involved in regulating structural lipid levels. We are in particular interested in triacylglycerol hydrolase, cholesterol esterase and a number of lipases. By developing novel and selective inhibitors of these enzymes, we can begin to probe their role in a number of disease states in an attempt to elucidate the endogenous role of carboxylesterases. In addition, we are employing lipidomics applications to profile the effects of anti-hyperlipidemic agents upon lipid homeostasis in combination with esterase inhibitors.