Elucidating the molecular mechanism of noncompetitive inhibition of acetylcholinesterase by an antidiabetic drug chlorpropamide: identification of new allosteric sites.

Acetylcholinesterase (AChE) has emerged as an important drug target for the treatment of neurodegenerative disorders such as Alzheimer's disease (AD). Recent experimental studies indicate that certain antidiabetic drugs can be repurposed as potent AChE inhibitors. Enzymatic kinetic assays suggest that the antidiabetic drug chlorpropamide (CPM) acts as a noncompetitive inhibitor, but the mechanism of action and the binding site(s) of interaction with AChE are not known. In this work, we have carried out molecular dynamics (MD) simulations to discover a new allosteric site in addition to the known peripheral anionic site (PAS) as a potential binding site of this noncompetitive inhibitor. We show that the conformational ensemble of the catalytic triad, particularly the HIS447, undergoes a significant population shift on ligand binding that is responsible for deactivation of the enzyme. We also elucidate the pathway of the allosteric signaling in terms of locally correlated domains of the inter-residue interaction network. Thus, our work identifies a new allosteric site for AChE inhibition and eludiates the underlying mechanistic principles. These results would be useful for the rational design of new noncompetitive inhibitors for AChE.