Abstract

In this study, we investigate the thermodynamic mechanisms by which electron transfer proteins adapt to environmental temperature by directly comparing the redox properties and folding stability of a psychrophilic cytochrome c and a mesophilic homolog. Our model system consists of two cytochrome c₆ proteins from diatoms: one adapted specifically to polar environments, the other adapted generally to surface ocean environments. Direct electrochemistry shows that the midpoint potential for the mesophilic homolog is slightly higher at all temperatures measured. Cytochrome c₆ from the psychrophilic diatom unfolds with a melting temperature 10.4 °C lower than the homologous mesophilic cytochrome c₆. Changes in free energy upon unfolding are identical, within error, for the psychrophilic and mesophilic protein; however, the chemical unfolding transition of the psychrophilic cytochrome c₆ is more cooperative than for the mesophilic cytochrome c₆. Substituting alanine residues found in the mesophile with serine found in corresponding positions of the psychrophile demonstrates that burial of the polar serine both decreases the thermal stability and decreases the midpoint potential. The mutagenesis data, combined with differences in the m-value of chemical denaturation, suggest that differences in solvent accessibility of the hydrophobic core underlie the adaptation of cytochrome c₆ to differing environmental temperature.

Graphic abstract

中文翻译：

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丙氨酸到丝氨酸的取代驱动嗜冷硅藻细胞色素c6的热适应。

摘要

在这项研究中，我们通过直接比较嗜冷细胞色素c和嗜温同源物的氧化还原特性和折叠稳定性来研究电子转移蛋白适应环境温度的热力学机制。我们的模型系统由硅藻中的两种细胞色素c ₆蛋白组成：一种专门适应极性环境，另一种通常适应海洋表面环境。直接电化学表明，在所有测得的温度下，嗜温同源物的中点电势略高。来自嗜冷硅藻的细胞色素c ₆的解链温度低于同源嗜温细胞色素c _6的10.4°C。嗜温和嗜温蛋白在展开时自由能的变化是相同的，但有误差。然而，嗜冷细胞色素的化学解折叠过渡Ç ₆比用于中温的细胞色素更合作Ç ₆。用在嗜冷菌的相应位置发现的丝氨酸代替在嗜温菌中发现的丙氨酸残基，表明掩埋极性丝氨酸既降低了热稳定性，又降低了中点电位。诱变数据，加上化学变性的m值的差异，表明疏水核溶剂可及性的差异是细胞色素c ₆适应的基础。 适应不同的环境温度。

图形摘要