Allosteric Binding Sites of Aβ Peptides on the Acetylcholine Synthesizing Enzyme ChAT as Deduced by In Silico Molecular Modeling

The native function of amyloid-beta (A beta) peptides is still unexplored. However, several recent reports suggest a prominent role of A beta peptides in acetylcholine homeostasis. To clarify this role of A beta, we have reported that A beta peptides at physiological concentrations can directly enhance the catalytic efficiency of the key cholinergic enzyme, choline acetyltransferase (ChAT), via an allosteric interaction. In the current study, we further aimed to elucidate the underlying ChAT-A beta interaction mechanism using in silico molecular docking and dynamics analysis. Docking analysis suggested two most probable binding clusters on ChAT for A beta(40) and three for A beta(42). Most importantly, the docking results were challenged with molecular dynamic studies of 100 ns long simulation in triplicates (100 ns x 3 = 300 ns) and were analyzed for RMSD, RMSF, RoG, H-bond number and distance, SASA, and secondary structure assessment performed together with principal component analysis and the free-energy landscape diagram, which indicated that the ChAT-A beta complex system was stable throughout the simulation time period with no abrupt motion during the evolution of the simulation across the triplicates, which also validated the robustness of the simulation study. Finally, the free-energy landscape analysis confirmed the docking results and demonstrated that the ChAT-A beta complexes were energetically stable despite the unstructured nature of C- and N-terminals in A beta peptides. Overall, this study supports the reported in vitro findings that A beta peptides, particularly A beta(4)(2), act as endogenous ChAT-Potentiating-Ligand (CPL), and thereby supports the hypothesis that one of the native biological functions of A beta peptides is the regulation of acetylcholine homeostasis.