氨基酸环境对电子附着于DNA的影响：双极性形式的作用
Role of Native and Zwitterionic Glycine in Electron Attachment to DNA: From Dipole-Bound to Solvent-Bound Doorway States
AI总结：
研究发现双极性甘氨酸通过门控机制增强电子附着，同时提高对电子的捕获和屏蔽能力，从而增强DNA的抗损伤性。
摘要：
我们利用胸腺嘧啶甘氨酸作为模型系统，研究了氨基酸双极性形式对电子附着于DNA的影响。在甘氨酸存在下，电子附着于胸腺嘧啶通过一种“门控机制”，其中初始阴离子状态的电子密度远离胸腺嘧啶的核框架。电子通过电子和核自由度的混合转移到核碱基，并且甘氨酸在调节电子转移速率中起重要作用。双极性甘氨酸中的电荷分离使它们比原生甘氨酸更能捕获电子，并能更好地屏蔽 incoming 电子。然而，在 bulk 溶剂化胸腺嘧啶阴离子中，双极性甘氨酸的存在不会导致核碱基的质子转移，这使其更具有抗碱基损伤的韧性。
英文摘要：
Electron attachment to DNA is strongly influenced by its molecular environment, yet the role of amino acids under physiologically relevant conditions remains poorly understood. Here, we investigate the effect of native and zwitterionic glycine on electron attachment to thymine using high-level electron-affinity calculations and QM/MM molecular dynamics simulations. Under micro-solvated conditions, electron attachment occurs through a dipole-bound doorway state that evolves into a valence-bound anion via nonadiabatic coupling. The zwitterionic form of glycine strengthens stabilization of the diffuse electron owing to its larger internal charge separation, whereas the stability of the valence-bound anion is determined by the hydrogen-bonding geometry. Barrier-free proton transfer is observed only for specific binding motifs and substantially stabilizes the thymine-centered anion. In bulk solution, the doorway mechanism persists, with a solvent-bound state replacing the dipole-bound state as the initial electron-trapping state. The larger electrostatic field of zwitterionic glycine delays electron localization on thymine, while permanent proton transfer is observed only in selected native glycine trajectories and is absent throughout the present simulations of zwitterionic glycine. Despite these differences in electron-transfer dynamics, both amino acid forms provide similar stabilization of the thymine-centered anion after solvent reorganization. Our results establish the solvent-bound state as the condensed-phase analogue of the dipole-bound doorway state and reveal how amino acid environments modulate electron attachment pathways in realistic DNA systems.
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