p.L286H Leu286His (p.L314H Leu314His in primary sequence with 28 amino-acids signal peptide) Phosphotriesterase activity Identical to WT. Tentative to place an Histidine in the active site at other place than the G117H mutation. Though the L286H mutant reactivated 400-fold more slowly than G117H, it was still 250-fold faster than wild-type BChE. Adjusting the position of histidine 286 by adding glycine residues to the sequence, e.g., L286GH, L286HG, and L286GHG, did not improve the reactivation rate
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.
        
Title: A single amino acid substitution, Gly117His, confers phosphotriesterase (organophosphorus acid anhydride hydrolase) activity on human butyrylcholinesterase Lockridge O, Blong RM, Masson P, Froment MT, Millard CB, Broomfield CA Ref: Biochemistry, 36:786, 1997 : PubMed
The G117H mutant of human butyrylcholinesterase (EC 3.1.1.8) was expressed in Chinese hamster ovary cells. Substitution of Gly 117 with His to make the G117H mutant endowed butyrylcholinesterase with the ability to catalyze the hydrolysis of organophosphate esters. G117H was still able to hydrolyze butyrylthiocholine, benzoylcholine, and o-nitrophenyl butyrate, but in addition it had acquired the ability to hydrolyze the antiglaucoma drug echothiophate and the pesticide paraoxon. Wild-type butyrylcholinesterase was irreversibly inhibited by echothiophate and paraoxon, but G117H regained 100% activity within 2-3 min following reaction with these compounds. On a polyacrylamide gel, the same bands that stained for activity with butyrylthiocholine also stained for activity with echothiophate. G117H is the only enzyme known that hydrolyzes echothiophate. Diethoxyphosphorylated G117H aged with a half-time of 5.5 h, a rate 600 times slower than the rate of hydrolysis. Echothiophate and paraoxon were hydrolyzed with the same kcat of 0.75 min-1. This calculates to a rate acceleration of 100,000-fold for hydrolysis of echothiophate and paraoxon by the G117H mutant compared to the nonenzymatic rate.