Substrate and Product Trafficking through the Active Center Gorge of Acetylcholinesterase Analyzed by Crystallography and Equilibrium Binding

Abstract

The principal role of acetylcholinesterase (AChE) 3 at cholinergic synapses is to terminate neurotransmission by fast hydrolysis of the substrate, acetylcholine (ACh) (1, 2). The AChE active center, containing the catalytic triad, Glu 334 -His 447 -Ser 203 in mammals (3), is located centrosymmetric to the subunit and at the base of a deep and narrow gorge (4, 5).AChE-catalyzed hydrolysis of ACh and other carboxyl esters proceeds via formation of an initial noncovalent enzyme-substrate complex.

Synthesis and in silico evaluation of 1N-methyl-1S-methyl-2-nitroethylene (NMSM) derivatives against Alzheimer disease: to understand their interacting mechanism with acetylcholinesterase

“…The residues of Trp86, Gly122, Ser203, Phe295, Phe297, and His447 are actively participating in VdW contacts, which are involved in substrate trafficking of ACh to the catalytic site. All these interactions and distance values are in good agreement with that of reported crystal structure of ACh/mAChE (mouse AChE) complex [17]. However, in Lig_6-bound hAChE-ACh complex, the substrate molecule is positioned in PAS site instead of binding with CT region of hAChE due to the active participation of Lig_6 in both PAS and CAS site with the GOLD score of 34.163.…”

“…The N3 (P pKa 07.78) of this ligand ideally positioned for a hydrogen bonding with OG group of Ser125 with distance of 3.08 Å. The nitro group establishes three HBs, in which O5 forms two HBs with OH of Tyr124 (P p K a 018.40) (2.88 Å), and Tyr337 (P p K a 018.25) (2.97 Å), which is a mediator residue for the mid-point of the diameter gorge [17] and responsible for the regulation of substrate and product trafficking. Atom O6 of the nitro group forms a hydrogen bond with Tyr124 with a distance of 2.75 Å.…”

“…The methylsulfanyl group faces the six-membered ring of the Trp86 indole by the active C-H-π interaction with a distance of 3.23 Å, which is similar to cation-π interaction as observed in the ACh-hAChE complex. The benzyl group of this ligand forms two adjacent site-stacked interaction with Tyr124 by the distance of 4.09 Å (Tyr124 CZ-C12 Lig_1) and 3.87 Å (Tyr124 CE1-C13 Lig_1), which is crucial residues of PAS site and helping for substrate binding and trafficking [17]. These results reveal that this ligand can span the entire gorge of hAChE, which might attribute to the inhibition of Aβ deposition and to the reduction in the hydrolysis of ACh (Fig.…”

“…Most of the administered drugs interact with the CT of AChE [15,16]. Furthermore, their interaction with residues (Trp86 and Tyr337) of catalytic anionic subsite (CAS), placed in close proximity to the active site, influences the hydrolysis of ACh [9,13,[17][18][19]. Besides the CT and CAS, the residues of peripheral anionic site (PAS; Tyr72, Asp74, Tyr124, Trp286, and Tyr341) also influence the function of AChE through their allosteric effects [16,20,21].…”

“…Besides the CT and CAS, the residues of peripheral anionic site (PAS; Tyr72, Asp74, Tyr124, Trp286, and Tyr341) also influence the function of AChE through their allosteric effects [16,20,21]. Residues of PAS trap the substrate molecules as they enter the gorge, and are involved in accelerating the transfer of the substrate acyl group to a serine hydroxyl group in CAS [17,18,[22][23][24][25]. In addition, PAS site is potentially responsible for colocalization of amyloid-β (Aβ) peptide in the brains of AD patients and has been shown to accelerate the assembly of Aβ to form amyloid fibrils [26][27][28].…”