2xmd

Publication Abstract from PubMed

Organophosphylates (OPs) exert their acute toxicity through inhibition of acetylcholinesterase, by phosphylation of the catalytic serine. Engineering of human butyrylcholinesterase by substitution of histidine for glycine at position 117 led to the creation of OP hydrolase activity. But the lack of structural information and poor understanding of the hydrolytic mechanism of G117H has hampered further improvements in the catalytic activity. We solved the crystallographic structure of the G117H mutant with a variety of ligands in the active site. A sulfate anion bound to the active site suggested the positioning for an OP prior to phosphylation. A fluoride anion was found in the active site when NaF was added to the crystallization buffer. In the fluoride complex, the imidazole ring from His117 was substantially shifted adopting a relaxed conformation most likely close to that of the unliganded mutant enzyme. Additional X-ray structures were obtained from the transient covalent adducts formed upon reaction of G117H with the OPs echothiophate and VX. The position of His117 shifted in response to the introduction of these adducts, overlaying the phosphylserine. These structural data suggest that the dephosphylation mechanism involves either a substantial conformational change of His117 or an adjacent nucleophilic substitution by water.

X-ray crystallographic snapshots of reaction intermediates in the G117H mutant of human butyrylcholinesterase, a nerve agent target engineered into a catalytic bioscavenger.,Nachon F, Carletti E, Wandhammer M, Nicolet Y, Schopfer LM, Masson P, Lockridge O Biochem J. 2010 Nov 19. PMID:21091433^[3]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.