A conformational change in the peripheral anionic site of Torpedo californica acetylcholinesterase induced by a bis-imidazolium oxime.
As part of ongoing efforts to design improved nerve agent antidotes, two X-ray crystal structures of Torpedo californica acetylcholinesterase (TcAChE) bound to the bis-pyridinium oxime, Ortho-7, or its experimental bis-imidazolium analogue, 2BIM-7, were determined. Bis-oximes contain two oxime groups connected by a hydrophobic linker. One oxime group of Ortho-7 binds at the entrance to the active-site gorge near Trp279, and the second binds at the bottom near Trp84 and Phe330. In the Ortho-7-TcAChE complex the oxime at the bottom of the gorge was directed towards the nucleophilic Ser200. In contrast, the oxime group of 2BIM-7 was rotated away from Ser200 and the oxime at the entrance induced a significant conformational change in the peripheral anionic site (PAS) residue Trp279. The conformational change alters the surface of the PAS and positions the imidazolium oxime of 2BIM-7 further from Ser200. The relatively weaker binding and poorer reactivation of VX-inhibited, tabun-inhibited or sarin-inhibited human acetylcholinesterase by 2BIM-7 compared with Ortho-7 may in part be owing to the unproductively bound states caught in crystallo. Overall, the reactivation efficiency of 2BIM-7 was comparable to that of 2-pyridine aldoxime methyl chloride (2-PAM), but unlike 2-PAM the bis-imidazolium oxime lacks a fixed charge, which may affect its membrane permeability.
CBMSE, U.S. Naval Research Laboratory, 4555 Overlook Avenue, Washington, DC 20375, USA.
Patricia M
PM
Legler
Bacterial Diseases, Walter Reed Army Institute of Research, 503 Robert Grant Avenue, Silver Spring, MD 20910, USA.
Iswarduth
I
Soojhawon
Division of Biochemistry, Walter Reed Army Institute of Research, 503 Robert Grant Avenue, Silver Spring, MD 20910, USA.
Charles B
CB
Millard
D000110:Acetylcholinesterase / Q000737:chemistry*; D000818:Animals; D000838:Anions; D001665:Binding Sites; D018360:Crystallography, X-Ray; D007093:Imidazoles / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D010091:Oximes / Q000737:chemistry*; D014101:Torpedo
D000838:Anions; D007093:Imidazoles; D010091:Oximes; D000110:Acetylcholinesterase
acetylcholinesterase; allosterism; organophosphate; oxime; peripheral anionic site