Department of Physics, Ben-Gurion University of the Negev, Beer Sheva, Israel.
Biophys J. 2010 Nov 3;99(9):2766-74. doi: 10.1016/j.bpj.2010.08.051.
The chemotaxis network of the bacterium Escherichia coli is perhaps the most studied model for adaptation of a signaling system to persistent stimuli. Although adaptation in this system is generally considered to be precise, there has been little effort to quantify this precision, or to understand how and when precision fails. Using a Förster resonance energy transfer-based reporter of signaling activity, we undertook a systematic study of adaptation kinetics and precision in E. coli cells expressing a single type of chemoreceptor (Tar). Quantifiable loss of precision of adaptation was observed at levels of the attractant MeAsp as low 10 μM, with pronounced differences in both kinetics and precision of adaptation between addition and removal of attractant. Quantitative modeling of the kinetic data suggests that loss of precise adaptation is due to a slowing of receptor methylation as available modification sites become scarce. Moreover, the observed kinetics of adaptation imply large cell-to-cell variation in adaptation rates-potentially providing genetically identical cells with the ability to "hedge their bets" by pursuing distinct chemotactic strategies.
细菌大肠杆菌的趋化网络可能是研究信号系统适应持续刺激的最成熟模型。尽管这个系统中的适应通常被认为是精确的，但很少有人努力量化这种精度，或者理解精度是如何以及何时失效的。我们使用基于Förster 共振能量转移的信号活性报告器，对表达单一类型趋化受体 (Tar) 的大肠杆菌细胞的适应动力学和精度进行了系统研究。在 10 μM 左右的低浓度的引诱剂 MeAsp 水平下，观察到适应精度可量化的损失，在添加和去除引诱剂时，适应的动力学和精度都有明显的差异。对动力学数据的定量建模表明，适应精度的丧失是由于可用修饰位点变得稀缺时，受体甲基化速度减慢所致。此外，观察到的适应动力学意味着适应率存在很大的细胞间差异——这可能为遗传上相同的细胞提供了“分散风险”的能力，从而采用不同的趋化策略。
