Molecular biology of cholinesterases: a background and an introduction

Molecular Modeling on Berberine Derivatives toward BuChE: An Integrated Study with Quantitative Structure-Activity Relationships Models, Molecular Docking, and Molecular Dynamics Simulations

A dataset of 67 berberine derivatives for the inhibition of butyrylcholinesterase (BuChE) was studied based on the combination of quantitative structure-activity relationships models, molecular docking, and molecular dynamics methods. First, a series of berberine derivatives were reported, and their inhibitory activities toward butyrylcholinesterase (BuChE) were evaluated. By 2D- quantitative structure-activity relationships studies, the best model built by partial least-square had a conventional correlation coefficient of the training set (R(2)) of 0.883, a cross-validation correlation coefficient (Qcv2) of 0.777, and a conventional correlation coefficient of the test set (Rpred2) of 0.775. The model was also confirmed by Y-randomization examination. In addition, the molecular docking and molecular dynamics simulation were performed to better elucidate the inhibitory mechanism of three typical berberine derivatives (berberine, C2, and C55) toward BuChE. The predicted binding free energy results were consistent with the experimental data and showed that the van der Waals energy term (ΔEvdw) difference played the most important role in differentiating the activity among the three inhibitors (berberine, C2, and C55). The developed quantitative structure-activity relationships models provide details on the fine relationship linking structure and activity and offer clues for structural modifications, and the molecular simulation helps to understand the inhibitory mechanism of the three typical inhibitors. In conclusion, the results of this study provide useful clues for new drug design and discovery of BuChE inhibitors from berberine derivatives.

X-ray crystallographic snapshots of reaction intermediates in the G117H mutant of human butyrylcholinesterase, a nerve agent target engineered into a catalytic bioscavenger

OPs (organophosphylates) exert their acute toxicity through inhibition of acetylcholinesterase, by phosphylation of the catalytic serine residue. Engineering of human butyrylcholinesterase, by substitution of a histidine residue for the glycine residue at position 117, led to the creation of OP hydrolase activity. However, the lack of structural information and poor understanding of the hydrolytic mechanism of the G117H mutant has hampered further improvements in the catalytic activity. We have solved the crystallographic structure of the G117H mutant with a variety of ligands in its active site. A sulfate anion bound to the active site suggested the positioning for an OP prior to phosphylation. A fluoride anion was found in the active site when NaF was added to the crystallization buffer. In the fluoride complex, the imidazole ring from the His117 residue was substantially shifted, adopting a relaxed conformation probably close to that of the unliganded mutant enzyme. Additional X-ray structures were obtained from the transient covalent adducts formed upon reaction of the G117H mutant with the OPs echothiophate and VX [ethyl ({2-[bis(propan-2-yl)amino]ethyl}sulfanyl](methyl)phosphinate]. The position of the His117 residue shifted in response to the introduction of these adducts, overlaying the phosphylserine residue. These structural data suggest that the dephosphylation mechanism involves either a substantial conformational change of the His117 residue or an adjacent nucleophilic substitution by water.

The structure of G117H mutant of butyrylcholinesterase: nerve agents scavenger

Organophosphate ester (OP) compounds are known for their ubiquitous use as insecticides. At the same time, these chemicals are highly toxic and can be used as nerve agents. G117H mutant of human Butyrylcholinesterase (BChE) was found to be capable of hydrolyzing certain OPs and protect against their toxicity. However, for therapeutic use, the rate of hydrolysis is too low. Its catalytic power can be improved by rational design, but the structure of the G117H mutant is first required. In this work, we determined, computationally, the three dimensional structure of the G117H BChE mutant. The structure was then validated by simulating acetylation of acetylthiocholine (ATC). Several plausible conformers of G117H BChE were examined but only the (62,-75) conformer fully reproduced catalytic effect. The (62,-75) conformer is, therefore, suggested as the structure adopted by the G117H BChE mutant. This conformer is shown to explain the loss of esterase activity observed for the G122H Acetylcholinesterase mutant together with its recovery when additional mutations are placed turning the enzyme also into an OP hydrolase. Furthermore, similarity of the structure to the structure of RNase A, which is known to hydrolyze the O--P bond in RNA, grants it further credibility and suggests a mechanism for the OP hydrolysis.

Inhibition effects of benactyzine and drofenine on human serum butyrylcholinesterase

Benactyzine and drofenine are widely used anticholinergic drugs. Benactyzine is used to treat organophosphate poisoning and drofenine acts on smooth muscle to stop muscle spasms. Both of these drugs are esters. After they enter the bloodstream, they will interact with butyrylcholinesterase (BChE; acylcholine acyl hydrolase: EC 3.1.1.8), which has an ability to hydrolyze a wide variety of esters. Therefore, the kinetic analysis of their inhibitory effects on human serum BChE was examined using butyrylthiocholine as substrate. Both drugs were competitive inhibitors of BChE and the Ki values of benactyzine and drofenine were calculated to be 0.010 +/- 0.001 and 0.003 +/- 0.000 mM, respectively, using the Systat (version 5.03, 1991) nonlinear regression analysis software package. According to these parameters, drofenine is a more potent competitive inhibitor of BChE than benactyzine.

Invited review: Anticholinesterases: dramatic aspects of their use and misuse

While the lore of anticholinesterases (antiChEs), particularly physostigmine and its natural source, the Calabar bean, is a subject of ethnomedicine and predates our scientific era, the pharmacological development of physostigmine analogues and related agents and of the antiChEs of the organophosphorus (OP) type, is a matter of the last two centuries; this development has reached an exponential character in the last fifty years. This explosion relates to certain uses and misuses of these drugs and this aspect of antiChEs is the main focus of this article. Firstly, there is the matter of Senile Dementia of Alzheimer's Type (SDAT); while there are several clinical applications of antiChEs, their employment in the treatment of SDAT is the last and most intense foray in their medical history and this article will focus on the uses and misuses of antiChEs in this area. Secondly, the applied use of antiChEs as insecticides which coincided with the historical development of OP antiChEs was and is, of major significance for the agricultural economy of both advanced and underdeveloped countries, as this employment may mean the difference between life and starvation. However, there are notable dangers with this application of OP drugs, as will be emphasized in this article. Thirdly, there is the significant and tragic development of the OP drugs as warfare agents and tools for terrorists and rogue states and this article will discuss the several types of toxicity of OP agents and their mechanisms, the enigma of the Persian Gulf War Syndrome being particularly stressed. Altogether, the immense range of antiChE topics includes areas of great basic interest and of practical applications that are of significant benefit to mankind as well as of potential danger.

Surface and Spectroscopic Properties of Acetylcholinesterase Monolayer at the Air/Water Interface

The behavior of the enzyme acetylcholinesterase was studied at the air/water interface. Surface pressure-area (pi-A) isotherms and UV-vis spectra recorded at different surface pressures were determined for different salt concentrations in the subphase. The ionic strength of the subphase does not influence the physical properties in consideration; however, the pH of the subphase has a great effect on its surface and optical properties. A subphase at pH 6.5 has shown that the enzyme is highly stable, based on the pi-A compression/decompression isotherms. No changes in the area per molecule were observed when the surface pressure was maintained constant at 16 mN/m for a period of 120 min. The long-term stability of acetylcholinesterase at the air/water interface was demonstrated for pH 6.5 and a salt concentration of 10(-2) M (KCl). The absorption spectra of the monolayer, measured directly at the air/water interface, are considered good evidence of the organization of the enzyme molecules. Copyright 1997 Academic Press. Copyright 1997Academic Press