Understanding the molecular mechanism of aryl acylamidase activity of acetylcholinesterase - An in silico study

A Comprehensive Review of Cholinesterase Modeling and Simulation

The present article reviews published efforts to study acetylcholinesterase and butyrylcholinesterase structure and function using computer-based modeling and simulation techniques. Structures and models of both enzymes from various organisms, including rays, mice, and humans, are discussed to highlight key structural similarities in the active site gorges of the two enzymes, such as flexibility, binding site location, and function, as well as differences, such as gorge volume and binding site residue composition. Catalytic studies are also described, with an emphasis on the mechanism of acetylcholine hydrolysis by each enzyme and novel mutants that increase catalytic efficiency. The inhibitory activities of myriad compounds have been computationally assessed, primarily through Monte Carlo-based docking calculations and molecular dynamics simulations. Pharmaceutical compounds examined herein include FDA-approved therapeutics and their derivatives, as well as several other prescription drug derivatives. Cholinesterase interactions with both narcotics and organophosphate compounds are discussed, with the latter focusing primarily on molecular recognition studies of potential therapeutic value and on improving our understanding of the reactivation of cholinesterases that are bound to toxins. This review also explores the inhibitory properties of several other organic and biological moieties, as well as advancements in virtual screening methodologies with respect to these enzymes.

Elucidation of binding mechanism of dibutyl phthalate on bovine serum albumin by spectroscopic analysis and molecular docking method

Dibutyl phthalate has been illegally used in beverages and directly affects the human health. Herein, the interaction occurred between dibutyl phthalate and bovine serum albumin was studied. The experimental results demonstrated that dibutyl phthalate could bind to bovine serum albumin and statically quench the intrinsic fluorescence of this protein. Circular dichroism measurements proved that the binding of dibutyl phthalate would lead to an obvious decrease of α-helix content in the bovine serum albumin. Molecular docking analysis clarified the fluorescence quenching mechanism, size distribution and zeta potential variation, conformational change of BSA, the site marker competitive fluorescence quenching and the interaction mechanism of dibutyl phthalate to bovine serum albumin. This work provided a useful information for the binding of dibutyl phthalate to protein.

The significance of aryl acylamidase activity of acetylcholinesterase in osteoblast differentiation and mineralization

Osteoblast differentiation is an essential event in the developmental process, which is favoured by the production of extra cellular matrix proteins and various enzymes including discrete ones like acetylcholinesterase (AChE). Despite the fact that AChE facilitates osteoblast differentiation, the significance of its catalytic functions [esterase and aryl acylamidase (AAA) activities] in the process is yet to be ascertained. In this context, SaOS-2 cell line was used in the present study to implicate the catalytic activities of AChE in process of osteoblast differentiation and mineralization. During differentiation, it was found that the activity of both esterase and AAA increased 1.13 and 1.46 folds respectively, signifying the involvement of catalytic activities of AChE in the process. Inhibition of both the catalytic activities of AChE with edrophonium significantly reduced the amount of mineralization by decreasing the alkaline phosphatase (ALP) activity and expression of differentiation-related genes such as RUNX-2, COL1A, ALP, OC, and OP significantly (p < 0.05). Inhibition of esterase activity without altering the AAA activity using gallamine significantly increased the level ALP activity and expression of differentiation-associated genes (p < 0.05), thus favouring mineralization. Therefore, this study concludes and confirms that the AAA activity of AChE is actively involved in the process of osteoblast differentiation and mineralization.

Endochondral Ossification Is Accelerated in Cholinesterase-Deficient Mice and in Avian Mesenchymal Micromass Cultures

Most components of the cholinergic system are detected in skeletogenic cell types in vitro, yet the function of this system in skeletogenesis remains unclear. Here, we analyzed endochondral ossification in mutant murine fetuses, in which genes of the rate-limiting cholinergic enzymes acetyl- (AChE), or butyrylcholinesterase (BChE), or both were deleted (called here A-B+, A+B-, A-B-, respectively). In all mutant embryos bone growth and cartilage remodeling into mineralizing bone were accelerated, as revealed by Alcian blue (A-blu) and Alizarin red (A-red) staining. In A+B- and A-B- onset of mineralization was observed before E13.5, about 2 days earlier than in wild type and A-B+ mice. In all mutants between E18.5 to birth A-blu staining disappeared from epiphyses prematurely. Instead, A-blu+ cells were dislocated into diaphyses, most pronounced so in A-B- mutants, indicating additive effects of both missing ChEs in A-B- mutant mice. The remodeling effects were supported by in situ hybridization (ISH) experiments performed on cryosections from A-B- mice, in which Ihh, Runx2, MMP-13, ALP, Col-II and Col-X were considerably decreased, or had disappeared between E18.5 and P0. With a second approach, we applied an improved in vitro micromass model from chicken limb buds that allowed histological distinction between areas of cartilage, apoptosis and mineralization. When treated with the AChE inhibitor BW284c51, or with nicotine, there was decrease in cartilage and accelerated mineralization, suggesting that these effects were mediated through nicotinic receptors (α7-nAChR). We conclude that due to absence of either one or both cholinesterases in KO mice, or inhibition of AChE in chicken micromass cultures, there is increase in cholinergic signalling, which leads to increased chondroblast production and premature mineralization, at the expense of incomplete chondrogenic differentiation. This emphasizes the importance of cholinergic signalling in cartilage and bone formation.

Acetylcholinesterase Regulates Skeletal In Ovo Development of Chicken Limbs by ACh-Dependent and -Independent Mechanisms

Formation of the vertebrate limb presents an excellent model to analyze a non-neuronal cholinergic system (NNCS). Here, we first analyzed the expression of acetylcholinesterase (AChE) by IHC and of choline acetyltransferase (ChAT) by ISH in developing embryonic chicken limbs (stages HH17-37). AChE outlined formation of bones, being strongest at their distal tips, and later also marked areas of cell death. At onset, AChE and ChAT were elevated in two organizing centers of the limb anlage, the apical ectodermal ridge (AER) and zone of polarizing activity (ZPA), respectively. Thereby ChAT was expressed shortly after AChE, thus strongly supporting a leading role of AChE in limb formation. Then, we conducted loss-of-function studies via unilateral implantation of beads into chicken limb anlagen, which were soaked in cholinergic components. After varying periods, the formation of cartilage matrix and of mineralizing bones was followed by Alcian blue (AB) and Alizarin red (AR) stainings, respectively. Both acetylcholine (ACh)- and ChAT-soaked beads accelerated bone formation in ovo. Notably, inhibition of AChE by BW284c51, or by the monoclonal antibody MAB304 delayed cartilage formation. Since bead inhibition of BChE was mostly ineffective, an ACh-independent action during BW284c51 and MAB304 inhibition was indicated, which possibly could be due to an enzymatic side activity of AChE. In conclusion, skeletogenesis in chick is regulated by an ACh-dependent cholinergic system, but to some extent also by an ACh-independent aspect of the AChE protein.