Department of Microsystems Engineering, University of Freiburg, Freiburg, Germany.
Department of Microsystems Engineering, University of Freiburg, Freiburg, Germany; Princeton University, Princeton, New Jersey.
Biophys J. 2018 Apr 24;114(8):1955-1969. doi: 10.1016/j.bpj.2018.02.043.
The wall-less, helical bacterial genus Spiroplasma has a unique propulsion system; it is not driven by propeller-like flagella but by a membrane-bound, cytoplasmic, linear motor that consists of a contractile chain of identical proteins spanning the entire cell length. By a coordinated spread of conformational changes of the proteins, kinks propagate in pairs along the cell body. However, the mechanisms for the initiation or delay of kinks and their coordinated spread remain unclear. Here, we show how we manipulate the initiation of kinks, their propagation velocities, and the time between two kinks for a single cell trapped in an optical line potential. By interferometric three-dimensional shape tracking, we measured the cells' deformations in response to various external stress situations. We observed a significant dependency of force generation on the cells' local ligand concentrations (likely ATP) and ligand hydrolysis, which we altered in different ways. We developed a mechanistic, mathematical model based on Kramer's rates, describing the subsequent cooperative and conformational switching of the chain's proteins. The model reproduces our experimental observations and can explain deformation characteristics even when the motor is driven to its extreme. Nature has invented a set of minimalistic mechanical driving concepts. To understand or even rebuild them, it is essential to reveal the molecular mechanisms of such protein chain motors, which need only two components-coupled proteins and ligands-to function.
无壁、螺旋状的细菌属螺菌具有独特的推进系统；它不是由类似于螺旋桨的鞭毛驱动，而是由一个膜结合的、细胞质的、线性的马达驱动，这个马达由一个横跨整个细胞长度的、由相同蛋白质组成的可收缩链组成。通过蛋白质构象变化的协调扩展，扭结成对地沿着细胞体传播。然而，扭结的起始或延迟及其协调传播的机制仍不清楚。在这里，我们展示了如何操纵被困在光阱中的单个细胞中扭结的起始、它们的传播速度以及两个扭结之间的时间间隔。通过干涉三维形状跟踪，我们测量了细胞对各种外部应力情况的变形。我们观察到力的产生与细胞局部配体浓度（可能是 ATP）和配体水解之间存在显著的依赖性，我们以不同的方式改变了这些依赖性。我们基于 Kramer 速率开发了一个机械的、数学的模型，描述了链中蛋白质的后续协同和构象转换。该模型再现了我们的实验观察结果，即使在将马达驱动到极限时，也可以解释变形特征。大自然发明了一套极简主义的机械驱动概念。为了理解甚至重建它们，揭示这种蛋白链马达的分子机制是至关重要的，这种马达只需要两个组件——耦合蛋白和配体——就可以发挥作用。
