Abstract
Kinetic studies and molecular modeling of human acetylcholinesterase (AChE) inhibition by a fluorinated acetophenone derivative, 1-(3-tert-butylphenyl)-2,2,2-trifluoroethanone (TFK), were performed. Fast reversible inhibition of AChE by TFK is of competitive type with Ki = 5.15 nM. However, steady state of inhibition is reached slowly. Kinetic analysis showed that TFK is a slow-binding inhibitor (SBI) of type B with Ki* = 0.53 nM. Reversible binding of TFK provides a long residence time, τ = 20 min, on AChE. After binding, TFK acylates the active serine, forming an hemiketal. Then, disruption of hemiketal (deacylation) is slow. AChE recovers full activity in approximately 40 min. Molecular docking and MD simulations depicted the different steps. It was shown that TFK binds first to the peripheral anionic site. Then, subsequent slow induced-fit step enlarged the gorge, allowing tight adjustment into the catalytic active site. Modeling of interactions between TFK and AChE active site by QM/MM showed that the “isomerization” step of enzyme-inhibitor complex leads to a complex similar to substrate tetrahedral intermediate, a so-called “transition state analog”, followed by a labile covalent intermediate. SBIs of AChE show prolonged pharmacological efficacy. Thus, this fluoroalkylketone intended for neuroimaging, could be of interest in palliative therapy of Alzheimer’s disease and protection of central AChE against organophosphorus compounds.
Highlights
Fluoroalkylketones (FAK) are potent inhibitors of acetyl cholinesterase (AChE, ES.3.1.1.7) and butyrylcholinesterase (BChE, EC.3.1.1.8) [1,2,3,4]
We investigated the effect of pre-incubation by TFK (1–10 nM) on inhibition of huAChE by 50 nM paraoxon under the same conditions
Molecular docking was performed using as targets several structures of hAChE co-crystallized with different non-covalent inhibitors (PDB ID 4EY4-4EY8 [15]) and one covalently bound to an organophosphorus adduct
Summary
Fluoroalkylketones (FAK) are potent inhibitors of acetyl cholinesterase (AChE, ES.3.1.1.7) and butyrylcholinesterase (BChE, EC.3.1.1.8) [1,2,3,4]. A characteristic of inhibition by these compounds is the slow establishment of equilibrium between enzyme and inhibitor. This process is called slow-binding inhibition (SBI). Three types of SBI have been described: (1) type A is characterized by a single step mechanism with slow kon and koff; (2) type B is a two-step mechanism: after rapid formation of a first enzyme-inhibitor complex, a slow induced-fit step occurs; (3) type C results from the existence of several enzyme forms in slow equilibrium that determine a slow conformational selection for inhibition [5]. The X-ray structure of Torpedo californica AChE-TMTFA complex (PDB ID 1AMN [6]) showed that the tight interactions between the enzyme and inhibitor are similar to interactions that take place in the enzyme active center with acetylcholine in the transition state [6]. Possible modulation and/or protection of AChE by TFK against OP phosphylation was explored
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