Scharf B E, Fahrner K A, Turner L, Berg H C
Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
Proc Natl Acad Sci U S A. 1998 Jan 6;95(1):201-6. doi: 10.1073/pnas.95.1.201.
The motile behavior of the bacterium Escherichia coli depends on the direction of rotation of its flagellar motors. Binding of the phosphorylated signaling molecule CheY to a motor component FliM is known to enhance clockwise rotation. It is difficult to study this interaction in vivo, because the dynamics of phosphorylation of CheY by its kinase CheA and the hydrolysis of CheY (accelerated by CheZ) are not under direct experimental control. Here, we examine instead the interaction with the flagellar motor of a double mutant CheY13DK106YW that is active without phosphorylation. The behavioral assays were carried out on tethered cells lacking CheA and CheZ. The effects of variation in intracellular concentration of the mutant protein were highly nonlinear. However, they can be explained by a thermal isomerization model in which the free energies of clockwise and counterclockwise states depend linearly on the amount of CheY bound.
大肠杆菌的运动行为取决于其鞭毛马达的旋转方向。已知磷酸化信号分子CheY与马达组件FliM的结合会增强顺时针旋转。在体内研究这种相互作用很困难，因为CheY被其激酶CheA磷酸化以及CheY水解（由CheZ加速）的动力学不在直接实验控制之下。在这里，我们转而研究一种无需磷酸化就具有活性的双突变体CheY13DK106YW与鞭毛马达的相互作用。行为分析是在缺乏CheA和CheZ的系留细胞上进行的。突变蛋白细胞内浓度变化的影响是非线性的。然而，它们可以用一种热异构化模型来解释，在该模型中，顺时针和逆时针状态的自由能线性依赖于结合的CheY的量。
