title: X-ray crystallographic snapshots of reaction intermediates in the G117H mutant of human butyrylcholinesterase, a nerve agent target engineered into a catalytic bioscavenger.
abstract: OPs (organophosphylates) exert their acute toxicity through inhibition of acetylcholinesterase, by phosphylation of the catalytic serine residue. Engineering of human butyrylcholinesterase, by substitution of a histidine residue for the glycine residue at position 117, led to the creation of OP hydrolase activity. However, the lack of structural information and poor understanding of the hydrolytic mechanism of the G117H mutant has hampered further improvements in the catalytic activity. We have solved the crystallographic structure of the G117H mutant with a variety of ligands in its 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 the His117 residue was substantially shifted, adopting a relaxed conformation probably close to that of the unliganded mutant enzyme. Additional X-ray structures were obtained from the transient covalent adducts formed upon reaction of the G117H mutant with the OPs echothiophate and VX [ethyl ({2-[bis(propan-2-yl)amino]ethyl}sulfanyl](methyl)phosphinate]. The position of the His117 residue shifted in response to the introduction of these adducts, overlaying the phosphylserine residue. These structural data suggest that the dephosphylation mechanism involves either a substantial conformational change of the His117 residue or an adjacent nucleophilic substitution by water.
authors.affiliation: Cellule Enzymologie, Département de Toxicologie, Institut de Recherche Biomédicale des Armées-CRSSA, 24 avenue des Maquis du Grésivaudan, La Tronche, France. florian@nachon.net
authors.forename: Florian
authors.initials: F
authors.lastname: Nachon
authors.forename: Eugenie
authors.initials: E
authors.lastname: Carletti
authors.forename: Marielle
authors.initials: M
authors.lastname: Wandhammer
authors.forename: Yvain
authors.initials: Y
authors.lastname: Nicolet
authors.forename: Lawrence M
authors.initials: LM
authors.lastname: Schopfer
authors.forename: Patrick
authors.initials: P
authors.lastname: Masson
authors.forename: Oksana
authors.initials: O
authors.lastname: Lockridge
mesh_terms: D019943:Amino Acid Substitution; D002091:Butyrylcholinesterase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004456:Echothiophate Iodide / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008958:Models, Molecular; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D009943:Organophosphorus Compounds; D009946:Organothiophosphorus Compounds / Q000494:pharmacology; D015202:Protein Engineering; D011961:Receptors, Fc
chemical_list: D002091:Butyrylcholinesterase; D004456:Echothiophate Iodide; D009943:Organophosphorus Compounds; D009946:Organothiophosphorus Compounds; D011961:Receptors, Fc; C045281:IgA receptor; C009680:VX-agent