在气相中观察到的钠化模型肽的动力学捕获液态构象
Kinetically Trapped Liquid-State Conformers of a Sodiated Model Peptide Observed in the Gas Phase
摘要：
我们调查的肽AcPheAla 5LysH+，研究在气相中的螺旋形成的模型系统，以充分了解稳定的螺旋结构的力量。特别是，我们解决的问题，是否在肽的C-末端的正电荷的局部固定是形成螺旋的先决条件，通过替换质子化的C-末端赖氨酸残基由丙氨酸和钠阳离子。低温冷却离子的气相振动光谱与基于密度泛函理论（DFT）的分子模拟相结合，允许详细的结构阐明。对于钠化的AcPheAla 6，我们发现球状而不是螺旋结构，因为移动的正电荷强烈地与肽骨架相互作用并破坏二级结构的形成。有趣的是，来自模拟的全局最小结构在实验中不存在。我们解释说，这是由于参与重新安排肽-阳离子相互作用，最终导致在实验中观察到的动力学捕获结构的高障碍。
英文摘要：
We investigate the peptide AcPheAla5LysH+, a model system for studying helix formation in the gas phase, in order to fully understand the forces that stabilize the helical structure. In particular, we address the question of whether the local fixation of the positive charge at the peptide's C-terminus is a prerequisite for forming helices by replacing the protonated C-terminal Lys residue by Ala and a sodium cation. The combination of gas-phase vibrational spectroscopy of cryogenically cooled ions with molecular simulations based on density-functional theory (DFT) allows for detailed structure elucidation. For sodiated AcPheAla6, we find globular rather than helical structures, as the mobile positive charge strongly interacts with the peptide backbone and disrupts secondary structure formation. Interestingly, the global minimum structure from simulation is not present in the experiment. We interpret that this is due to high barriers involved in re-arranging the peptide-cation interaction that ultimately result in kinetically trapped structures being observed in the experiment.
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