Peripheral site and acyl pocket define selective inhibition of mouse butyrylcholinesterase by two biscarbamates

In this study we related metacarb (N-(2-(3,5-bis(dimethylcarbamoyloxy)phenyl)-2-hydroxyethyl)propan-2-aminium chloride) and isocarb (N-(2-(3,4-bis(dimethylcarbamoyloxy)phenyl)-2-hydroxyethyl)propan-2-aminium chloride) inhibition selectivity, as well as stereoselectivity of mouse acetylcholinesterase (AChE; 3.1.1.7) and butyrylcholinesterase (BChE; 3.1.1.8) to the active site residues by studying the progressive inhibition of AChE, BChE and six AChE mutants with racemic and (R)-enantiomers of metacarb and isocarb. Metacarb and isocarb proved to be very potent BChE inhibitors with inhibition rate constants in the range of 103–104 M−1 s−1. For metacarb and isocarb, inhibition of BChE w.t. was 260 and 35 times, respectively, faster than inhibition of AChE w.t. For four mutants inhibition was faster than for AChE w.t. but none reached the inhibition rate of BChE. The highest increase in the inhibition rate (about 30 times for metacarb and 13 times for isocarb) was achieved with mutants F295L/Y337A and Y124Q meaning that selective inhibition of mouse BChE is dictated mainly by two amino acids from BChE: leucine 286 from the acyl pocket and glutamine 119 from the peripheral site. Wild type enzymes displayed pronounced stereoselectivity for (R)-enantiomers of metacarb and isocarb. Interestingly, the residues that define selective inhibition of mouse BChE by biscarbamates also affect the stereoselectivity of enzymes.