Structural and dynamic effects of paraoxon binding to human acetylcholinesterase by X-ray crystallography and inelastic neutron scattering

Organophosphorus (OP) compounds, including nerve agents and some pesticides, covalently bind to the catalytic serine of human acetylcholinesterase (hAChE), thereby inhibiting acetylcholine hydrolysis necessary for efficient neurotransmission. Oxime antidotes can reactivate the OP-conjugated hAChE, but reactivation efficiency can be low for pesticides, such as paraoxon (POX). Understanding structural and dynamic determinants of OP inhibition and reactivation can provide insights to design improved reactivators. Here, X-ray structures of hAChE with unaged POX, with POX and oximes MMB4 and RS170B, and with MMB4 are reported. A significant conformational distortion of the acyl loop was observed upon POX binding, being partially restored to the native conformation by oximes. Neutron vibrational spectroscopy combined with molecular dynamics simulations showed that picosecond vibrational dynamics of the acyl loop soften in the ∼20–50 cm−1 frequency range. The acyl loop structural perturbations may be correlated with its picosecond vibrational dynamics to yield more comprehensive template for structure-based reactivator design. [Display omitted] •Structures of hAChE with POX and oximes show unseen acyl loop conformations•Marked distortions of the acyl loop in POX-hAChE reverse only in part upon oxime binding•Inelastic neutron scattering from POX-hAChE is stronger than that from native hAChE•MD shows vibrational dynamics softening of the acyl loop, not of Ω loop or dimer interface Gerlits et al. used X-ray crystallography to visualize conformational plasticity of the acyl loop in human acetylcholinesterase upon paraoxon and subsequent oxime reactivator binding. Using inelastic neutron scattering the study visualized softening of the acyl loop vibrational dynamics in the paraoxon-conjugated enzyme providing insights for reactivator design.