TY - JOUR
T1 - Organophosphorus acid anhydride hydrolase activity in human butyrylcholinesterase
T2 - Synergy results in a somanase
AU - Millard, Charles B.
AU - Lockridge, Oksana
AU - Broomfield, Clarence A.
PY - 1998/1/6
Y1 - 1998/1/6
N2 - Organophosphorus acid anhydride (OP) 'nerve agents' are rapid, stoichiometric, and essentially irreversible inhibitors of serine hydrolases. By placing a His near the oxyanion hole of human butyrylcholinesterase (BChE), we made an esterase (G117H) that catalyzed the hydrolysis of several OP, including sarin and VX [Millard et al. (1995) Biochemistry 34, 15925- 15930]. G117H was limited, however, because it was irreversibly inhibited by pinacolyl methylphosphonofluoridate (soman); soman is among the most toxic synthetic poisons known. This limitation of G117H has been overcome by a new BChE (G117H/E197Q) that combines two engineered features: spontaneous dephosphonylation and slow aging (dealkylation). G117H/E197Q was compared with the single mutants BChE G117H and E197Q. Each retained cholinesterase activity with butyrylthiocholine as substrate, although k(cat)/K(m) decreased 11-, 11- or 110-fold for purified G117H, E197Q, or G117H/E197Q, respectively, as compared with wild-type BChE. Only G117H/E197Q catalyzed soman hydrolysis; all four soman stereoisomers as well as satin and VX were substrates. Phosphonylation and dephosphonylation reactions were stereospecific. Double mutant thermodynamic cycles suggested that the effects of the His and G1n substitutions on phosphonylation were additive for P(S)C(R) or P(R)C(R) soman, but were cooperative for the P(S)C(S) stereoisomer. Dephosphonylation limited overall OP hydrolysis with apparent rate constants of 0.006, 0.077, and 0.128 min-1 for the P(R/S)/C(R), P(S)C(S), and P(R)C(S) stereoisomerase, respectively, at pH 7.5, 25 °C. We conclude that synergistic protein design converted an archetypal 'irreversible inhibitor' into a slow substrate for the target enzyme.
AB - Organophosphorus acid anhydride (OP) 'nerve agents' are rapid, stoichiometric, and essentially irreversible inhibitors of serine hydrolases. By placing a His near the oxyanion hole of human butyrylcholinesterase (BChE), we made an esterase (G117H) that catalyzed the hydrolysis of several OP, including sarin and VX [Millard et al. (1995) Biochemistry 34, 15925- 15930]. G117H was limited, however, because it was irreversibly inhibited by pinacolyl methylphosphonofluoridate (soman); soman is among the most toxic synthetic poisons known. This limitation of G117H has been overcome by a new BChE (G117H/E197Q) that combines two engineered features: spontaneous dephosphonylation and slow aging (dealkylation). G117H/E197Q was compared with the single mutants BChE G117H and E197Q. Each retained cholinesterase activity with butyrylthiocholine as substrate, although k(cat)/K(m) decreased 11-, 11- or 110-fold for purified G117H, E197Q, or G117H/E197Q, respectively, as compared with wild-type BChE. Only G117H/E197Q catalyzed soman hydrolysis; all four soman stereoisomers as well as satin and VX were substrates. Phosphonylation and dephosphonylation reactions were stereospecific. Double mutant thermodynamic cycles suggested that the effects of the His and G1n substitutions on phosphonylation were additive for P(S)C(R) or P(R)C(R) soman, but were cooperative for the P(S)C(S) stereoisomer. Dephosphonylation limited overall OP hydrolysis with apparent rate constants of 0.006, 0.077, and 0.128 min-1 for the P(R/S)/C(R), P(S)C(S), and P(R)C(S) stereoisomerase, respectively, at pH 7.5, 25 °C. We conclude that synergistic protein design converted an archetypal 'irreversible inhibitor' into a slow substrate for the target enzyme.
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U2 - 10.1021/bi972057c
DO - 10.1021/bi972057c
M3 - Article
C2 - 9425044
AN - SCOPUS:0032488593
SN - 0006-2960
VL - 37
SP - 237
EP - 247
JO - Biochemistry
JF - Biochemistry
IS - 1
ER -