在前面的文章中,我们提出了电压门控离子通道(VGIC)超家族的灵活性分析。在这项研究中,我们详细描述了有关6TM离子通道演化的电压传感器域(VSD)和孔域(PD)的灵活性曲线。特别是,我们强调了灵活性在CNG通道出现中的作用,并描述了原型VSD和TolQ蛋白之间的显著序列相似性.据报道,这些膜蛋白具有高度柔性的S4样片段,表现出Lys而不是Arg。序列分析表明,除了这个类似S4的部分,TolQ蛋白还显示与来自典型V-传感器的S2和S3中的特定基序的相似性。值得注意的是,来自典型VSD的S3柔性谱和TolQ蛋白中的S3样也是相似的。有趣的是,来自早期不同原核生物的TolQ比现代生物或真正的V传感器中的TolQ相对更灵活。关于警局,我们还发现,早期原核生物中的2TMK+通道比现代微生物中的通道灵活得多,并且这种灵活性与CNG通道中存在的灵活性相当。电压依赖性主要表现在VSD是刚性的原核CNG通道中,而真核CNG通道则更加灵活且V依赖性差。CNG渠道中存在的灵活性的含义,讨论了它们对环核苷酸的敏感性和阳离子选择性。最后,我们生成了一个推定的环核苷酸调制离子通道的结构模型,我们在这里创造了AqK,来自嗜热细菌Aquifexaeolicus,已知最早的发散原核生物之一。总的来说,我们的分析表明,CNG样通道中的V传感器在早期原核生物中基本上是刚性的,但增加了该模块可能是细菌鞭毛马达复合体的非常柔性的定子蛋白的一部分的可能性.
In the preceding article, we present a flexibility analysis of the voltage-gated ion channel (VGIC) superfamily. In this study, we describe in detail the flexibility profile of the voltage-sensor domain (VSD) and the pore domain (PD) concerning the evolution of 6TM ion channels. In particular, we highlight the role of flexibility in the emergence of CNG channels and describe a significant level of sequence similarity between the archetypical VSD and the TolQ proteins. A highly flexible S4-like segment exhibiting Lys instead Arg for these membrane proteins is reported. Sequence analysis indicates that, in addition to this S4-like segment, TolQ proteins also show similarity with specific motifs in S2 and S3 from typical V-sensors. Notably, S3 flexibility profiles from typical VSDs and S3-like in TolQ proteins are also similar. Interestingly, TolQ from early divergent prokaryotes are comparatively more flexible than those in modern counterparts or true V-sensors. Regarding the PD, we also found that 2TM K+-channels in early prokaryotes are considerably more flexible than the ones in modern microbes, and such flexibility is comparable to the one present in CNG channels. Voltage dependence is mainly exhibited in prokaryotic CNG channels whose VSD is rigid whereas the eukaryotic CNG channels are considerably more flexible and poorly V-dependent. The implication of the flexibility present in CNG channels, their sensitivity to cyclic nucleotides and the cation selectivity are discussed. Finally, we generated a structural model of the putative cyclic nucleotide-modulated ion channel, which we coined here as AqK, from the thermophilic bacteria Aquifex aeolicus, one of the earliest diverging prokaryotes known. Overall, our analysis suggests that V-sensors in CNG-like channels were essentially rigid in early prokaryotes but raises the possibility that this module was probably part of a very flexible stator protein of the bacterial flagellum motor complex.