Redesign of Butylcholinesterase for Cocaine Metabolism

This project focuses on the rational redesign of human butyrylcholinesterase (BChE) in order to accelerate cocaine metabolism in man. Enhancing cocaine metabolism by administration of BChE has been recognized as a possible treatment strategy for cocaine overdose and addiction. However, the catalytic activity of this plasma enzyme is three orders-of-magnitude lower against the naturally occurring (-)-cocaine than that against the relatively biologically inactive (+)-cocaine isomer. (+)-cocaine can be cleared from plasma in seconds prior to partitioning into the central nervous system. The long-term goal of this project is to guide the construction of a BChE mutant using site-directed mutagenesis by our collaborators so that the mutant can be used as an exogenous enzyme in human body with a catalytic activity for (-)-cocaine comparable to that of wild-type BChE for (+)-cocaine. For this purpose, state-of-the-art computational techniques will be used to uncover the mechanistic difference of the enzymatic reaction between (-)-cocaine and (+)-cocaine and to establish a rational basis for theoretical design of BChE mutants with an improved activity for (-)-cocaine. The specific aims of the investigation involved in the present proposal include: 1. To determine structures and dynamics of the BChE binding with (-)-cocaine and (+)-cocaine, including the non-prereactive and prereactive BChE-substrate complexes. 2. To uncover fundamental reaction pathways for BChE-catalyzed hydrolysis of (-)-cocaine and (+)-cocaine at the benzoyl ester by performing reaction coordinate calculations on properly chosen model systems; 3. To investigate dynamics and changes of BChE binding with (-)-cocaine and (+)-cocaine during the enzymatic hydrolysis by carrying out MD simulations on the enzyme-reactant, transition state, intermediate and product complexes; 4. To evaluate free energy profiles and kinetics of the enzymatic hydrolysis by performing combined quantum mechanical and free energy perturbation calculations (QM-FE); 5. To design BChE mutants expected to have higher activity for (-)-cocaine based on the binding information obtained from Specific Aim 2 and the energetic information from Specific Aim 3.