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Effects of a cocaine hydrolase engineered from human butyrylcholinesterase on metabolic profile of cocaine in rats.

ABSTRACT: Accelerating cocaine metabolism through enzymatic hydrolysis at cocaine benzoyl ester is recognized as a promising therapeutic approach for cocaine abuse treatment. Our more recently designed A199S/F227A/S287G/A328W/Y332G mutant of human BChE, denoted as cocaine hydrolase-3 (CocH3), has a considerably improved catalytic efficiency against cocaine and has been proven active in blocking cocaine-induced toxicity and physiological effects. In the present study, we have further characterized the effects of CocH3 on the detailed metabolic profile of cocaine in rats administrated intravenously (IV) with 5 mg/kg cocaine, demonstrating that IV administration of 0.15 mg/kg CocH3 dramatically changed the metabolic profile of cocaine. Without CocH3 administration, the dominant cocaine-metabolizing pathway in rats was cocaine methyl ester hydrolysis to benzoylecgonine (BZE). With the CocH3 administration, the dominant cocaine-metabolizing pathway in rats became cocaine benzoyl ester hydrolysis to ecgonine methyl ester (EME), and the other two metabolic pathways (i.e. cocaine methyl ester hydrolysis to BZE and cocaine oxidation to norcocaine) became insignificant. The CocH3-catalyzed cocaine benzoyl ester hydrolysis to EME was so efficient such that the measured maximum blood cocaine concentration (?38 ng/ml) was significantly lower than the threshold blood cocaine concentration (?72 ng/ml) required to produce any measurable physiological effects.

SUBMITTER: Chen X

PROVIDER: S-EPMC5094907 | biostudies-literature | 2016 Nov

REPOSITORIES: biostudies-literature

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Effects of a cocaine hydrolase engineered from human butyrylcholinesterase on metabolic profile of cocaine in rats.

Chen Xiabin X Zheng Xirong X Zhou Ziyuan Z Zhan Chang-Guo CG Zheng Fang F

Chemico-biological interactions 20160503 Pt B

Accelerating cocaine metabolism through enzymatic hydrolysis at cocaine benzoyl ester is recognized as a promising therapeutic approach for cocaine abuse treatment. Our more recently designed A199S/F227A/S287G/A328W/Y332G mutant of human BChE, denoted as cocaine hydrolase-3 (CocH3), has a considerably improved catalytic efficiency against cocaine and has been proven active in blocking cocaine-induced toxicity and physiological effects. In the present study, we have further characterized the effe ...[more]

PMID: 27154495

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Project description:Butyrylcholinesterase (BChE)-cocaine binding and the fundamental pathway for BChE-catalyzed hydrolysis of cocaine have been studied by molecular modeling, molecular dynamics (MD) simulations, and ab initio calculations. Modeling and simulations indicate that the structures of the prereactive BChE/substrate complexes for (-)-cocaine and (+)-cocaine are all similar to that of the corresponding prereactive BChE/butyrylcholine (BCh) complex. The overall binding of BChE with (-)-cocaine and (+)-cocaine is also similar to that proposed with butyrylthiocholine and succinyldithiocholine, i.e., (-)- or (+)-cocaine first slides down the substrate-binding gorge to bind to Trp-82 and stands vertically in the gorge between Asp-70 and Trp-82 (nonprereactive complex) and then rotates to a position in the catalytic site within a favorable distance for nucleophilic attack and hydrolysis by Ser-198 (prereactive complex). In the prereactive complex, cocaine lies horizontally at the bottom of the gorge. The fundamental catalytic hydrolysis pathway, consisting of acylation and deacylation stages similar to those for ester hydrolysis by other serine hydrolases, was proposed on the basis of the simulated prereactive complex and confirmed theoretically by ab initio reaction coordinate calculations. Both the acylation and deacylation follow a double-proton-transfer mechanism. The calculated energetic results show that within the chemical reaction process the highest energy barrier and Gibbs free energy barrier are all associated with the first step of deacylation. The calculated ratio of the rate constant (k(cat)) for the catalytic hydrolysis to that (k(0)) for the spontaneous hydrolysis is approximately 9.0 x 10(7). The estimated k(cat)/k(0) value of approximately 9.0 x 10(7) is in excellent agreement with the experimentally derived k(cat)/k(0) value of approximately 7.2 x 10(7) for (+)-cocaine, whereas it is approximately 2000 times larger than the experimentally derived k(cat)/k(0) value of approximately 4.4 x 10(4) for (-)-cocaine. All of the results suggest that the rate-determining step of the BChE-catalyzed hydrolysis of (+)-cocaine is the first step of deacylation, whereas for (-)-cocaine the change from the nonprereactive complex to the prereactive complex is rate-determining and has a Gibbs free energy barrier higher than that for the first step of deacylation by approximately 4 kcal/mol. A further analysis of the structural changes from the nonprereactive complex to the prereactive complex reveals specific amino acid residues hindering the structural changes, providing initial clues for the rational design of BChE mutants with improved catalytic activity for (-)-cocaine.

Project description:Molecular dynamics (MD) simulations were carried out to study cocaine binding with wild-type human butyrylcholinesterase (BChE) and its mutants based on a recently reported X-ray crystal structure of human BChE. For each BChE-cocaine system, we simulated both the nonprereactive and prereactive complexes in water. Despite the significant difference found at the acyl binding pocket, the simulated structures confirm the fundamental structural and mechanistic insights obtained from earlier computational studies of wild-type BChE with cocaine based on a homology model, e.g. the rate-determining step for BChE-catalyzed hydrolysis of biologically active (-)-cocaine is the (-)-cocaine rotation in the active site from the nonprereactive BChE-(-)-cocaine complex to the prereactive complex. It has been demonstrated that the MD simulations on both the nonprereactive and prereactive BChE-cocaine complexes can clearly reveal whether specific mutations produce the desired BChE-(-)-cocaine binding structures in which the (-)-cocaine rotation is less hindered while the required prereactive BChE-(-)-cocaine binding is maintained. Based on the MD simulations, both A328W/Y332A and A328W/Y332G BChE's are expected to have catalytic activity for (-)-cocaine hydrolysis higher than that of wild-type BChE and the activity of A328W/Y332G BChE should be slightly higher than that of A328W/Y332A BChE due to the less-hindered (-)-cocaine rotation in the mutant BChE's. However, the less-hindered (-)-cocaine rotation is only a necessary condition for a higher activity mutant BChE. The (-)-cocaine rotation is also less hindered in A328W/Y332A/Y419S BChE, but (-)-cocaine binds with A328W/Y332A/Y419S BChE in a way that is not suitable for the catalysis. Thus, A328W/Y332A/Y419S BChE is expected to lose the catalytic activity. The computational predictions were confirmed by our experimental kinetic data, demonstrating that the MD simulation-based computational protocol used in this study is reliable in prediction of the catalytic activity of BChE mutants for (-)-cocaine hydrolysis.

Dataset Information

Effects of a cocaine hydrolase engineered from human butyrylcholinesterase on metabolic profile of cocaine in rats.

Publications

Effects of a cocaine hydrolase engineered from human butyrylcholinesterase on metabolic profile of cocaine in rats.

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