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How do chemical denaturants affect the mechanical folding and unfolding of proteins?

机译：化学变性剂如何影响蛋白质的机械折叠和展开？

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We present the first single-molecule atomic force microscopy study on the effect of chemical denaturants on the mechanical folding/Unfolding kinetics of a small protein GB1 (the B1 immunoglobulin-binding domain of protein G from Streptococcus). Upon increasing the concentration of the chemical denaturant guanidinium chloride (GdmCl), we observed a systematic decrease in the mechanical stability of GB1, indicating the softening effect of the chemical denaturant on the mechanical stability of proteins. This mechanical softening effect originates from the reduced free-energy barrier between the folded state and the unfolding transition state, which decreases linearly as a function of the denaturant concentration. Chemical denaturants, however, do not alter the mechanical unfolding pathway or shift the position of the transition state for mechanical unfolding. We also found that the folding rate constant of GB1 is slowed down by GdmCl in mechanical folding experiments. By combining the mechanical folding/unfolding kinetics of GB1 in GdmCl solution, we developed the "mechanical chevron plot" as a general tool to understand how chemical denaturants influence the mechanical folding/unfolding kinetics and free-energy diagram in a quantitative fashion. This study demonstrates great potential in combining chemical denaturation with single-molecule atomic force microscopy techniques to reveal invaluable information on the energy landscape underlying protein folding/unfolding reactions. (c) 2007 Elsevier Ltd. All rights reserved.
机译：我们提出了第一个单分子原子力显微镜研究化学变性剂对小蛋白质GB1（来自链球菌的蛋白质G的B1免疫球蛋白结合域）的机械折叠/展开动力学的影响。通过增加化学变性剂氯化胍（GdmCl）的浓度，我们观察到GB1的机械稳定性系统降低，表明化学变性剂对蛋白质的机械稳定性具有软化作用。这种机械软化效果源自折叠状态和展开过渡状态之间自由能垒的减少，自由能垒随变性剂浓度的增加而线性降低。然而，化学变性剂不会改变机械展开路径或改变过渡状态的位置以进行机械展开。我们还发现在机械折叠实验中，GdmCl降低了GB1的折叠速率常数。通过结合GB1在GdmCl溶液中的机械折叠/展开动力学，我们开发了“机械人字形图”作为通用工具，以了解化学变性剂如何以定量方式影响机械折叠/展开动力学和自由能图。这项研究证明了将化学变性与单分子原子力显微镜技术相结合的巨大潜力，从而揭示了有关蛋白质折叠/展开反应的能量格局的宝贵信息。 （c）2007 Elsevier Ltd.保留所有权利。

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