Department of Cell & Molecular Biology, Uppsala University, Biomedical Center, SE-751 24 Uppsala, Sweden.
Biochemistry. 2022 Apr 5;61(7):514-522. doi: 10.1021/acs.biochem.2c00024. Epub 2022 Mar 1.
The structural principles of enzyme cold adaptation are of fundamental interest both for understanding protein evolution and for biotechnological applications. It has become clear in recent years that structural flexibility plays a major role in tuning enzyme activity at low temperatures, which is reflected by characteristic changes in the thermodynamic activation parameters for psychrophilic enzymes, compared to those of mesophilic and thermophilic ones. Hence, increased flexibility of the enzyme surface has been shown to lead to a lower enthalpy and a more negative entropy of activation, which leads to higher activity in the cold. This immediately raises the question of how enzyme oligomerization affects the temperature dependence of catalysis. Here, we address this issue by computer simulations of the catalytic reaction of a cold-adapted bacterial short chain dehydrogenase in different oligomeric states. Reaction free energy profiles are calculated at different temperatures for the tetrameric, dimeric, and monomeric states of the enzyme, and activation parameters are obtained from the corresponding computational Arrhenius plots. The results show that the activation free energy, enthalpy, and entropy are remarkably insensitive to the oligomeric state, leading to the conclusion that assembly of the subunit interfaces does not compromise cold adaptation, even though the mobilities of interfacial residues are indeed affected.
酶低温适应的结构原则对于理解蛋白质进化和生物技术应用都具有根本意义。近年来，人们已经清楚地认识到，结构的灵活性在低温下调节酶活性方面起着重要作用，这反映在与中温和嗜热酶相比，嗜冷酶的热力学活化参数的特征变化上。因此，酶表面的灵活性增加导致较低的焓和更负的活化熵，从而导致在低温下更高的活性。这立即引发了一个问题，即酶的寡聚化如何影响催化的温度依赖性。在这里，我们通过计算机模拟来解决这个问题，模拟了一种低温适应的细菌短链脱氢酶在不同寡聚状态下的催化反应。为酶的四聚体、二聚体和单体状态计算了不同温度下的反应自由能曲线，并从相应的计算阿仑尼乌斯图中获得了活化参数。结果表明，活化自由能、焓和熵对寡聚状态的变化不敏感，这得出的结论是，亚基界面的组装并不会损害低温适应，即使界面残基的迁移率确实受到影响。
