p.G117C Gly117Cys (p.G145C Gly145Cys in primary sequence with 28 amino-acids signal peptide) Changing to acidic residues G117E and G117D were significantly reactive, but less nucleophilic residues such as G117S, G117C, and G117Y were not.
Kinetic parameters
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References:
Title: Mutants of human butyrylcholinesterase with organophosphate hydrolase activity; evidence that His117 is a general base catalyst for hydrolysis of echothiophate Schopfer LM, Boeck AT, Broomfield CA, Lockridge O Ref: Journal of Medicinal Chemistryical Biology Radiol Def, 2:1, 2004 : PubMed
Human butyrylcholinesterase (BChE, EC 3.1.1.8) is an efficient scavenger of nerve agents and organophosphorus (OP) pesticides; one molecule of BChE inactivates one molecule of OP in a suicide reaction that irreversibly inhibits BChE. By contrast the BChE mutant, G117H, inactivates many molecules of OP. The OP makes a covalent bond with the active site serine and then the serine is dephosphorylated by the action of His117. In an effort to understand the mechanism by which is 117 achieves dephosphorylation, 62 new mutants of human BChE were tested for OP hydrolase activity, using a new screening assay. It was found that not only G117H, but also G117D, G117E, and L286H mutants were OP hydrolases. These results support the hypothesis that a hydrogen-bond acceptor acts as a general base t activate a water molecule which in turn dephosphorylates the active site serine The screening assay provides a convenient means for identifying cholinesterase mutants with OP hydrolase activity.
