State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China.
State Key Laboratory of Biomembrane and Membrane Biotechnology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
Int J Mol Sci. 2009 Dec 23;10(12):5498-5512. doi: 10.3390/ijms10125498.
Hyperthermophilic superoxide dismutases (SODs) are of particular interest due to their potential industrial importance and scientific merit in studying the molecular mechanisms of protein folding and stability. Compared to the mesophilic SODs, the hyperthermostable Fe-SODs (TcSOD and ApSOD) have an extended C-terminal helix, which forms an additional ion-pairing network. In this research, the role of the extended C-terminus in the structural stability of TcSOD was studied by investigating the properties of two deletion mutants. The results indicated that the ion-pairing network at the C-terminus had limited contributions to the stability of TcSOD against heat- and GdnHCl-induced inactivation. The intactness of the C-terminal helix had dissimilar impact on the two stages of TcSOD unfolding induced by guanidinium chloride. The mutations slightly decreased the Gibbs free energy of the dissociation of the tetrameric enzymes, while greatly affected the stability of the molten globule-like intermediate. These results suggested that the additional ion-pairing network mainly enhanced the structural stability of TcSOD by stabilizing the monomers.
嗜热超氧化物歧化酶（SOD）因其在研究蛋白质折叠和稳定性的分子机制方面的潜在工业重要性和科学价值而备受关注。与中温 SOD 相比，嗜热 Fe-SOD（TcSOD 和 ApSOD）具有扩展的 C 端螺旋，形成额外的离子配对网络。在这项研究中，通过研究两种缺失突变体的特性，研究了 C 端扩展在 TcSOD 结构稳定性中的作用。结果表明，C 端的离子配对网络对 TcSOD 抵抗热和 GdnHCl 诱导失活的稳定性的贡献有限。C 端螺旋的完整性对盐酸胍诱导 TcSOD 展开的两个阶段有不同的影响。突变略微降低了四聚体酶解离的吉布斯自由能，而极大地影响了类熔球中间态的稳定性。这些结果表明，额外的离子配对网络主要通过稳定单体来增强 TcSOD 的结构稳定性。
