Lara Ortiz Maria Teresa, Martinell García Victor, Del Rio Gabriel
Department of Biochemistry and Structural Biology, Institute of Cellular Physiology at UNAM, Mexico City 04510, Mexico.
Int J Mol Sci. 2021 Sep 26;22(19):10359. doi: 10.3390/ijms221910359.
Cells adapt to different stress conditions, such as the antibiotics presence. This adaptation sometimes is achieved by changing relevant protein positions, of which the mutability is limited by structural constrains. Understanding the basis of these constrains represent an important challenge for both basic science and potential biotechnological applications. To study these constraints, we performed a systematic saturation mutagenesis of the transmembrane region of HokC, a toxin used by Escherichia coli to control its own population, and observed that 92% of single-point mutations are tolerated and that all the non-tolerated mutations have compensatory mutations that reverse their effect. We provide experimental evidence that HokC accumulates multiple compensatory mutations that are found as correlated mutations in the HokC family multiple sequence alignment. In agreement with these observations, transmembrane proteins show higher probability to present correlated mutations and are less densely packed locally than globular proteins; previous mutagenesis results on transmembrane proteins further support our observations on the high tolerability to mutations of transmembrane regions of proteins. Thus, our experimental results reveal the HokC transmembrane region high tolerance to loss-of-function mutations that is associated with low sequence conservation and high rate of correlated mutations in the HokC family sequences alignment, which are features shared with other transmembrane proteins.
细胞会适应不同的应激条件，比如抗生素的存在。这种适应有时是通过改变相关蛋白质的位置来实现的，而这些蛋白质位置的可变性受到结构限制。理解这些限制的基础对基础科学和潜在的生物技术应用而言都是一项重大挑战。为了研究这些限制，我们对HokC的跨膜区域进行了系统性饱和诱变，HokC是大肠杆菌用来控制自身种群数量的一种毒素，我们观察到92%的单点突变是可耐受的，并且所有不可耐受的突变都有能逆转其效应的补偿性突变。我们提供了实验证据，表明HokC积累了多个补偿性突变，这些突变在HokC家族的多序列比对中表现为相关突变。与这些观察结果一致，跨膜蛋白出现相关突变的概率更高，并且在局部比球状蛋白的堆积密度更低；先前关于跨膜蛋白的诱变结果进一步支持了我们对蛋白质跨膜区域突变高耐受性的观察。因此，我们的实验结果揭示了HokC跨膜区域对功能丧失突变具有高耐受性，这与HokC家族序列比对中低序列保守性和高相关突变率相关，而这些特征是其他跨膜蛋白所共有的。
