Small MscS-like mechanosensitive channels: understanding minimal requirements for structure and function

机械敏感通道是许多重要生物过程的分子基础。其中一个功能是对低渗休克的应激反应，这是单细胞生物在与环境直接接触时生存所必需的。其中一个通道是大肠杆菌（EcMscS）的小电导机械敏感通道。它是最大和最多样化的机械敏感通道家族中最具特征的成员。EcMscS被认为是机制核心，因为该家族的大多数其他成员都较大，具有额外的n端或c端延伸。在这里，我们想研究比EcMscS更小的类msc通道的罕见例子。我们从不同的生命领域中选择了三个例子：一个通道来自候选古菌（CwMscS），一个来自土拉弗朗西斯菌（FtMscS），另一个来自原生动物克氏锥虫（TcMscS）。这些通道要么缺乏有助于电压感应的n端区域，要么缺乏提供稳定性和选择性的特征前庭，或者两者兼而有之。我们想知道结构最小化的功能效果。为了回答这个问题，我们将利用电子冷冻显微镜确定三个较小的msc样通道的分子结构，并利用电生理学量化其功能特性。我们期望揭开一个古老的生物分子机器的基本细节，它广泛分布在生命的各个领域。

Mechanosensitive channels are the molecular basis of many important biological processes. One function is the stress response to hypoosmotic shock, which is essential for the survival of single-celled organisms in direct contact with the environment. One of these channels is the mechanosensitive channel of small conductance of Escherichia coli (EcMscS). It is the best characterized member of the largest and most diverse family of mechanosensitive channels. EcMscS is considered to be the mechanistic core because most of the other members of the family are larger with additional N-terminal or C-terminal extensions. Here, we want to investigate the rare examples of MscS-like channels that are smaller than EcMscS. We have chosen three examples from different domains of life: one channel comes from the Archaea Candidatus woesearchaeota archaeon (CwMscS), one from the bacterium, Francisella tularensis (FtMscS) and another from the protozoan Trypanosomas cruzi (TcMscS). These channels lack either N-terminal regions that contribute to the voltage sensing, or a characteristic vestibule that provides stability and selectivity, or both. We want to know what functional effects the structural minimization has. To answer this question, we will determine the molecular structures of the three smaller MscS-like channels with electron cryo microscopy and quantify the functional properties with electrophysiology. We expect to unveil essential nuts and bolts of an ancient, bio-molecular machine that is widely distributed across all domains of life.