Effects of viscosity and osmotic stress on the reaction of human butyrylcholinesterase with cresyl saligenin phosphate, a toxicant related to aerotoxic syndrome: kinetic and molecular dynamics studies

Abstract

CSP (cresyl saligenin phosphate) is an irreversible inhibitor of human BChE (butyrylcholinesterase) that has been involved in the aerotoxic syndrome. Inhibition under pseudo-first-order conditions is biphasic, reflecting a slow equilibrium between two enzyme states E and E'. The elementary constants for CSP inhibition of wild-type BChE and D70G mutant were determined by studying the dependence of inhibition kinetics on viscosity and osmotic pressure. Glycerol and sucrose were used as viscosogens. Phosphorylation by CSP is sensitive to viscosity and is thus strongly diffusion-controlled (kon≈10⁸ M⁻¹·min⁻¹). Bimolecular rate constants (ki) are about equal to kon values, making CSP one of the fastest inhibitors of BChE. Sucrose caused osmotic stress because it is excluded from the active-site gorge. This depleted the active-site gorge of water. Osmotic activation volumes, determined from the dependence of ki on osmotic pressure, showed that water in the gorge of the D70G mutant is more easily depleted than that in wild-type BChE. This demonstrates the importance of the peripheral site residue Asp⁷⁰ in controlling the active-site gorge hydration. MD simulations provided new evidence for differences in the motion of water within the gorge of wild-type and D70G enzymes. The effect of viscosogens/osmolytes provided information on the slow equilibrium E⇌E', indicating that alteration in hydration of a key catalytic residue shifts the equilibrium towards E'. MD simulations showed that glycerol molecules that substitute for water molecules in the enzyme active-site gorge induce a conformational change in the catalytic triad residue His⁴³⁸, leading to the less reactive form E'.

Novel conjugates of aminoadamantanes with carbazole derivatives as potential multitarget agents for AD treatment

“…The protein structure was prepared, saturated with water molecules, and optimized using QM/MM method as reported previously8283. The molecular docking with a Lamarckian Genetic Algorithm (LGA)84 was performed with the Autodock 4.2.685 and AutoDock Vina 1.1.2 software86.…”

Probing the Catalytic Mechanism of Copper Amine Oxidase from Arthrobacter globiformis with Halide Ions

“…Effect of Solvent Viscosity on AGAO Activity-To further probe the equilibrium shift between TPQ amr and TPQ sq , we examined the dependence of catalytic activity on solvent viscosity, which can perturb diffusion-controlled steps, including substrate binding, product release, and conformational changes of the enzyme (58,59). Glycerol (M r ϭ 92.1) and sucrose (M r ϭ 342.3) were used as viscogens.…”

Assessment of neurotoxic effects of tri-cresyl phosphates (TCPs) and cresyl saligenin phosphate (CBDP) using a combination of in vitro techniques

“…The different positioning of the methyl group might determine the activity at receptors or the reactivity with enzymes. This may explain why ToCP also via its metabolite CBDP, but not the other isomers, causes OPIDN by NTE inhibition (Johnson, 1990, Johnson andGlynn, 1995), and why it is reactive enough to build adducts with a variety of enzymes (Carletti, Schopfer, 2011, Masson et al , 2013, Schopfer et al , 2010. Further studies are needed to address the question whether ToCP directly interacts with the various glutamate receptors in cortical neurons.…”