Three distinct domains in the cholinesterase molecule confer selectivity for acetyl- and butyrylcholinesterase inhibitors

By examining inhibitor interactions with single and multiple site-specific mutants of mouse acetylcholinesterase, we have identified three distinct domains in the cholinesterase structure that are responsible for conferring selectivity for acetyl- and butyrylcholinesterase inhibitors. The first domain is the most obvious; it defines the constraints on the acyl pocket dimensions where the side chains of F 295 and F 297 primarily outline this region in acetylcholinesterase. Replacement of these phenylalanine side chains with the aliphatic residues found in butyrylcholinesterase allows for the catalysis of larger substrates and accommodates butyrylcholinesterase-selective alkyl phosphates such as isoOMPA. Also, elements of substrate activation characteristic of butyrylcholinesterase are evident in the F 297 I mutant