Kaimer Christine, Zusman David R
Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720, USA.
Mol Microbiol. 2016 Apr;100(2):379-95. doi: 10.1111/mmi.13323. Epub 2016 Feb 9.
The Frz pathway of Myxococcus xanthus controls cell reversal frequency to support directional motility during swarming and fruiting body formation. Previously, we showed that phosphorylation of the response regulator FrzZ correlates with reversal frequencies, suggesting that this activity represents the output of the Frz pathway. Here, we tested the effect of different expression levels of FrzZ and its cognate kinase FrzE on M. xanthus motility. FrzZ overexpression caused a slight increase in phosphorylation and reversals. By contrast, FrzE overexpression abolished phosphorylation of FrzZ; this inhibition required the response regulator domain of FrzE. FrzZ phosphorylation was restored when both FrzE and FrzZ were overexpressed together. Our results show that the response regulator domain of FrzE is a negative regulator of FrzE kinase activity. This inhibition can be modulated by FrzZ, which acts as a positive regulator. Interestingly, fluorescence microscopy revealed that FrzZ and FrzE localize differently: FrzE colocalizes with the FrzCD receptor and the nucleoid, while FrzZ shows dispersed and polar localization. However, FrzZ binds tightly to the truncated variant FrzEΔ(CheY) . This indicates that the response regulator domain of FrzE is required for the interaction between FrzE and FrzZ to be transient, providing an unexpected regulatory output to the Frz pathway.
黄色黏球菌的Frz信号通路控制细胞反转频率，以支持群体运动和子实体形成过程中的定向运动。此前，我们发现反应调节因子FrzZ的磷酸化与反转频率相关，这表明该活性代表了Frz信号通路的输出。在此，我们测试了不同表达水平的FrzZ及其同源激酶FrzE对黄色黏球菌运动性的影响。FrzZ过表达导致磷酸化和反转略有增加。相比之下，FrzE过表达消除了FrzZ的磷酸化；这种抑制作用需要FrzE的反应调节结构域。当FrzE和FrzZ一起过表达时，FrzZ的磷酸化得以恢复。我们的结果表明，FrzE的反应调节结构域是FrzE激酶活性的负调节因子。这种抑制作用可由作为正调节因子的FrzZ进行调节。有趣的是，荧光显微镜显示FrzZ和FrzE的定位不同：FrzE与FrzCD受体和类核共定位，而FrzZ呈现分散和极性定位。然而，FrzZ与截短变体FrzEΔ(CheY)紧密结合。这表明FrzE的反应调节结构域是FrzE与FrzZ之间短暂相互作用所必需的，为Frz信号通路提供了意想不到的调节输出。
