Organophosphate (OP) inhibition of human carboxylesterase 1 (hCE1).

<p><b>A</b>. Three G-type OP nerve agents and OP model compound (R represents respective <i>O</i>-alkoxy groups). Wild-type hCE1 preferentially binds the stereoisomers shown (7). <b>B</b>. Schematic mechanism of OP hydrolysis by hCE1. X represents the leaving group and * denotes a non-reactive state.</p

Bimolecular rates of inhibition, Michaelis-Menten constants, and rates of reactivation for wild-type and V146H/L363E hCE1 against racemic cyclosarin and stereoisomers of cyclosarin model compounds.

<p>N = 3, s.d., N.D. is not determined, N.R. is no reactivation, pH 7.4, 25°C.</p>a<p>Racemic <i>bona fide</i> cyclosarin,</p>b<p>stereoisomers of cyclosarin model compounds,</p>c<p>(8).</p

Human carboxylesterase 1 active site structure.

<p>Active site of human carboxylesterase 1 covalently inhibited via S221 with cyclosarin (magenta) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0017441#pone.0017441-Hemmert1" target="_blank">[8]</a>. The other catalytic residues, in addition to S221, are H468 and E354 (yellow), and are surrounded by hydrophobic residues (grey surface) including V146 and L363 (light blue), as well as the oxyanion hole (white).</p

Catalytic efficiencies (<i>k</i>_cat/<i>K</i>_m) of engineered enzymes towards hemisubstrates.

a<p>(16).</p>b<p>(32).</p>c<p>(32).</p

Reactivation of hCE1 following nerve agent exposure.

<p><b>A</b>. Spontaneous reactivation of V146H/L363E hCE1 following inhibition by racemic sarin (blue), soman (green), or cyclosarin (red). Wild type hCE1 (grey) only reactivates following sarin inhibition (7). n = 6, s.d. <b>B</b>. Rates of dephosphonylation for hCE1 variants in the presence of sarin (blue), soman (green) and cyclosarin (red). n = 3, s.d.</p

Inhibition and Michaelis-Menten constants for wild-type and V146H/L363E hCE1 against stereoisomers of sarin and soman model compounds.

<p>(N = 3, s.d.)</p>a<p>(7).</p

Mechanism of reactivation by V146H/L363E hCE1 after cyclosarin binding.

<p><b>A</b>. Model of V146H/L363E (cyan) hCE1 with P<i>_R</i> cyclosarin (magenta) including a water molecule (red) between E363 and the central phosphorus. <b>B</b>. Proposed mechanism for enhanced reactivation following cyclosarin inhibition. <b>C</b>. pH dependence of V146H/L363E (black) and L363E (grey) hCE1 dephosphonylation following cyclosarin inhibition.</p