A mutant of platelet-activating factor acetylhydrolase hydrolyzes the nerve agent soman

Organophosphorus nerve agents (OPs) such as soman (GD) are the most toxic chemicals created. They exert toxic effects by inactivating acetylcholinesterase and binding to secondary targets in the bloodstream. Enzymes associated with lipoproteins, such as platelet-activating factor acetylhydrolase (PAFAH), have largely been ignored for engineering purposes due to complex interfacial kinetics and lack of structural data. We have expressed active human PAFAH in bacteria and crystallized the OP adducts. From these structures, we created histidine mutations (F322H, W298H, L153H) near the permissive active site to enhance turn-over of the phosphorylated serine. Wild-type PAFAH, L153H, and F322H have essentially no activity against GD, identical to rates from mock expressions. W298H developed novel somanase activity around 2–3.5 nmoles/hr/μg protein with a KM around 0.6mM at pH 7.5. There was no selective preference for any of the GD stereoisomers. Not since butyrylcholinesterase G117H has there been development of novel OP-hydrolase activity on an enzyme platform from a single mutation. DISCLAIMER: This research was supported by the Defense Threat Reduction Agency, Joint Science and Technology Office, Medical S&T Division. The opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the U.S. Army or the Department of Defense.