The NaChBac sodium channel from Bacillus halodurans is a homologue of eukaryotic voltage-gated sodium channels. It can be solubilized in a range of detergents and consists of four identical subunits assembled as a tetramer. Sodium channels are relatively flexible molecules, adopting different conformations in their closed, open and inactivated states. This study aimed to design and construct a mutant version of the NaChBac protein that would insert into membranes and retain its folded conformation, but which would have enhanced stability when subjected to thermal stress. Modelling studies suggested a G219S mutant would have decreased conformational flexibility due to the removal of the glycine hinge around the proposed gating region, thereby imparting increased resistance to unfolding. The mutant expressed in Escherichia coli and purified in the detergent dodecyl maltoside was compared to wildtype NaChBac prepared in a similar manner. The mutant was incorporated into the membrane fraction and had a nearly identical secondary structure to the wildtype protein. When the thermal unfolding of the G219S mutant was examined by circular dichroism spectroscopy, it was shown to not only have a Tm approximately 10 degrees C higher than the wildtype, but also in its unfolded state it retained more ordered helical structure than did the wildtype protein. Hence the G219S mutant was shown to be, as designed, more thermally stable.

中文翻译：

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G219S 诱变作为稳定细菌钠通道 NaChBac 构象灵活性的一种手段。

来自 Bacillus halodurans 的 NaChBac 钠通道是真核电压门控钠通道的同源物。它可以溶解在一系列去污剂中，由四个相同的亚基组装成一个四聚体。钠通道是相对灵活的分子，在其闭合、开放和失活状态下采用不同的构象。本研究旨在设计和构建 NaChBac 蛋白的突变体版本，该蛋白可以插入膜中并保留其折叠构象，但在受到热应力时会增强稳定性。建模研究表明，G219S 突变体会​​降低构象灵活性，因为去除了拟定门控区域周围的甘氨酸铰链，从而增加了对展开的抵抗力。将在大肠杆菌中表达并在去污剂十二烷基麦芽糖苷中纯化的突变体与以类似方式制备的野生型 NaChBac 进行比较。突变体被掺入膜部分并具有与野生型蛋白质几乎相同的二级结构。当通过圆二色光谱检查 G219S 突变体的热展开时，显示它不仅具有比野生型高约 10 摄氏度的 Tm，而且在其展开状态下，它比野生型蛋白质保留了更有序的螺旋结构. 因此，G219S 突变体被证明是，如设计的，更热稳定。当通过圆二色光谱检查 G219S 突变体的热展开时，显示它不仅具有比野生型高约 10 摄氏度的 Tm，而且在其展开状态下，它比野生型蛋白质保留了更有序的螺旋结构. 因此，G219S 突变体被证明是，如设计的，更热稳定。当通过圆二色光谱检查 G219S 突变体的热展开时，显示它不仅具有比野生型高约 10 摄氏度的 Tm，而且在其展开状态下，它比野生型蛋白质保留了更有序的螺旋结构. 因此，G219S 突变体被证明是，如设计的，更热稳定。