Fundamental reaction mechanism for cocaine hydrolysis in human butyrylcholinesterase

Chang Guo Zhan, Fang Zheng, Donald W. Landry

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134 Scopus citations

Abstract

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 (kcat) for the catalytic hydrolysis to that (k0) for the spontaneous hydrolysis is ∼9.0 × 107. The estimated kcat/k0 value of ∼9.0 × 107 is in excellent agreement with the experimentally derived kcat/k0 value of ∼7.2 × 107 for (+)-cocaine, whereas it is ∼2000 times larger than the experimentally derived kcat/k0 value of ∼4.4 × 104 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 ∼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.

Original languageEnglish
Pages (from-to)2462-2474
Number of pages13
JournalJournal of the American Chemical Society
Volume125
Issue number9
DOIs
StatePublished - Mar 5 2003

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry

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