Aminoalcoholate-driven tetracopper(II) cores as dual acetyl and butyrylcholinesterase inhibitors: Experimental and theoretical elucidation of mechanism of action.

Three coordination compounds featuring different types of tetracopper(II) cores, namely [O ⊂ Cu4{N(CH2CH2O)3}4(BOH)4][BF4]2 (1), [Cu4(µ4-H2edte)(µ5-H2edte)(sal)2]n·7nH2O, (H4edte = N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine, H2sal = salicylic acid) (2), and [{Cu4(µ3-Hbes)4(µ-hba)}K(H2O)3]n, H3bes = N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (3), were assayed for their potency to inhibit the acetyl (AChE) and butyrylcholinesterase (BuChE) enzymes aiming to test these compounds as potential dual inhibitors in the treatment of Alzheimer's disease. All the investigated compounds showed a strong inhibitory potency toward both enzymes with IC50 values in micromolar range of concentration; compound 1 displayed the most potent inhibitory behaviour toward both enzymes. The mechanism of the AChE and BuChE inhibition was examined by enzyme kinetic measurements. The obtained kinetic parameters, Vmax and Km indicated an uncompetitive type of inhibition of both enzymes by compound 1. For the other two compounds a non-competitive inhibition mode was observed. To get further insight into the mechanism of action and to elucidate binding modes in details we examined the interactions of 1-3 with acetylcholinesterase, using molecular docking approach. Grid based docking studies indicated that these compounds can bind to peripheral anionic site (PAS) of the AChE with Ki values in micromolar range. Moreover, blind docking revealed the capability of investigated compounds to bind to new allosteric site (i.e. binding site II) distinct from PAS. Showing that these Cu-based compounds can act as new allosteric inhibitors of AChE and identifying novel allosteric binding site on AChE represents a significant contribution toward the design of novel and more effective inhibitors of AChE.

Interaction of Au(iii) and Pt(ii) complexes with Na/K-ATPase: experimental and theoretical study of reaction stoichiometry and binding sites.

The present paper deals with investigation of the interaction between selected simple structure Au(iii) ([AuCl4]-, [AuCl2(dmso)2]+, [AuCl2(bipy)]+) and Pt(ii) ([PtCl2(dmso)2]) complexes with Na/K-ATPase as the target enzyme, using an experimental and theoretical approach. Reaction stoichiometries and binding constants for these enzyme/complex systems were determined, while kinetic measurements were used in order to reveal the type of inhibition. Based on the results obtained by quantum mechanical calculations (electrostatic surface potential (ESP), volume and surface of the complexes) the nature of the investigated complexes was characterized. By using the solvent accessible surface area (SASA) applied on specific inhibitory sites (ion channel and intracellular domains) the nature of these sites was described. Docking studies were used to determine the theoretical probability of the non-covalent metal binding site positions. Inhibition studies implied that all the investigated complexes decreased the activity of the enzyme while the kinetic analysis indicated an uncompetitive mode of inhibition for the selected complexes. Docking results suggested that the main inhibitory site of all these complexes is located in the ion translocation pathway on the extracellular side in the E2P enzyme conformation, similar to the case of cardiac glycosides, specific Na/K-ATPase inhibitors. Also, based on our knowledge, the hydrolyzed forms of [AuCl4]- and [PtCl2(dmso)2] complexes were investigated for the first time by theoretical calculations in this paper. Thereby, a new inhibitory site situated between the M2 and M4 helices was revealed. Binding in this site induces conformational changes in the enzyme domains and perturbs the E1-E2P conformational equilibrium, causing enzyme inhibition.