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 like 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. 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.

有机磷（OP）化合物，包括神经毒剂和一些农药，与人类乙酰胆碱酯酶（hAChE）的催化丝氨酸共价结合，从而抑制有效神经传递所必需的乙酰胆碱水解。肟类解毒剂能够重新激活与有机磷结合的hAChE，但对于对氧磷（POX）等农药，其重新激活效率可能较低。了解有机磷抑制和重新激活的结构及动态决定因素可为设计改进的激活剂提供思路。在此报道了hAChE与未老化的对氧磷、对氧磷及肟类化合物MMB4和RS170B以及与MMB4结合的X射线结构。观察到对氧磷结合时酰基环发生显著的构象扭曲，肟类化合物可使其部分恢复到天然构象。中子振动光谱结合分子动力学模拟表明，酰基环的皮秒振动动力学在约20 - 50 cm⁻¹频率范围内变软。酰基环的结构扰动可能与其皮秒振动动力学相关，从而为基于结构的激活剂设计提供更全面的模板。 格里茨等人利用X射线晶体学观察了对氧磷及随后的肟类激活剂结合时人类乙酰胆碱酯酶中酰基环的构象可塑性。通过非弹性中子散射，该研究观察到对氧磷结合的酶中酰基环振动动力学变软，为激活剂设计提供了思路。