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Phys. Rev. Lett:数学模型阐释力学对细菌鞭毛马达影响机制

来源:北京大学生物动态光学成像中心 2012-05-03 18:37

近日,北京大学生物动态光学成像中心的白凡副研究员在顶级物理期刊Physical Review Letters第108期发表了题为“Coupling between switching regulation and torque generation in bacterial flagellar motor” 的论文,用数学模型阐释了力学环境对细菌鞭毛马达反转的影响机制。

生物体具有“趋利避害”的本能。哪怕是只有几微米大小的初级生物形式-细菌,已经具有游向营养物,逃离危害物的能力。大肠杆菌(E.coli)的信号传导网络(signal transduction network)作为生物体信号传导最简单的一个例子,得到了广泛深入的研究。研究表明,大肠杆菌细胞表面分布的receptor能够感知外界环境的变化,并将这种变化传递反映为信号传递蛋白CheY的磷酸化浓度。磷酸化的CheY蛋白在细菌胞质内扩散,最终结合到细菌鞭毛马达的底部,导致马达多次反转,从而改变细菌运动的方向。过去的研究只发现了这种化学过程影响细菌鞭毛马达的反转,然而美国科学家Howard Berg组在2003年发表于Nature杂志上的结果首次揭示细菌所处的力学环境一样能影响细菌鞭毛马达的反转,其机制一直没有得到很好的解释。

在这篇文章中白凡副研究员与日本大阪大学難波啓一教授,美国Virginia Tech邢建华教授合作,在细菌鞭毛马达反转的conformational spread mechanism的基础上引入平均场近似理论,巧妙地用一个简单数学模型解释了外界力学环境对细菌鞭毛马达反转的影响机制。该模型的提出,为检验细菌对外界力学环境产生反应的实验研究奠定了理论基础,能带动一系列实验工作的开展。(生物谷Bioon.com)

Coupling between Switching Regulation and Torque Generation in Bacterial Flagellar Motor

Fan Bai1,2, Tohru Minamino2, Zhanghan Wu3, Keiichi Namba2,*, and Jianhua Xing

The bacterial flagellar motor plays a crucial role in both bacterial locomotion and chemotaxis. Recent experiments reveal that the switching dynamics of the motor depend on the rotation speed of the motor, and thus the motor torque, nonmonotonically. Here we present a unified mathematical model which treats motor torque generation based on experimental torque-speed curves and the torque-dependent switching based on the conformational spread model. The model successfully reproduces the observed switching rate as a function of the rotation speed, and provides a generic physical explanation independent of most details. A stator affects the switching dynamics through two mechanisms: accelerating the conformational flipping rate of individual rotor-switching units, which contributes most when the stator works at a high torque and thus a low speed; and influencing a larger number of rotor-switching units within unit time, whose contribution is the greatest when the motor rotates at a high speed. Consequently, the switching rate shows a maximum at intermediate speed, where the above two mechanisms find an optimal output. The load-switching relation may serve as a mechanism for sensing the physical environment, similar to the chemotaxis mechanism for sensing the chemical environment. It may also coordinate the switch dynamics of motors within the same cell.

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