Department of Mathematical and Life Sciences, Hiroshima University, Hiroshima, Japan.
Biophys J. 2012 Sep 19;103(6):1390-9. doi: 10.1016/j.bpj.2012.08.034.
Complex networks of interacting molecular components of living cells are responsible for many important processes, such as signal processing and transduction. An important challenge is to understand how the individual properties of these molecular interactions and biochemical transformations determine the system-level properties of biological functions. Here, we address the issue of the accuracy of signal transduction performed by a bacterial chemotaxis system. The chemotaxis sensitivity of bacteria to a chemoattractant gradient has been measured experimentally from bacterial aggregation in a chemoattractant-containing capillary. The observed precision of the chemotaxis depended on environmental conditions such as the concentration and molecular makeup of the chemoattractant. In a quantitative model, we derived the chemotactic response function, which is essential to describing the signal transduction process involved in bacterial chemotaxis. In the presence of a gradient, an analytical solution is derived that reveals connections between the chemotaxis sensitivity and the characteristics of the signaling system, such as reaction rates. These biochemical parameters are integrated into two system-level parameters: one characterizes the efficiency of gradient sensing, and the other is related to the dynamic range of chemotaxis. Thus, our approach explains how a particular signal transduction property affects the system-level performance of bacterial chemotaxis. We further show that the two parameters can be derived from published experimental data from a capillary assay, which successfully characterizes the performance of bacterial chemotaxis.
活细胞中相互作用的分子成分的复杂网络负责许多重要的过程，如信号处理和转导。一个重要的挑战是要理解这些分子相互作用和生化转化的个体特性如何决定生物功能的系统水平特性。在这里，我们研究了细菌趋化性系统进行信号转导的准确性问题。细菌对趋化梯度的趋化敏感性已经从含有趋化剂的毛细管中细菌聚集的实验中测量出来。观察到的趋化敏感性取决于环境条件，如趋化剂的浓度和分子组成。在定量模型中，我们推导出了趋化响应函数，这对于描述涉及细菌趋化性的信号转导过程至关重要。在梯度存在的情况下，我们推导出了一个解析解，揭示了趋化敏感性与信号系统特征（如反应速率）之间的联系。这些生化参数被整合到两个系统水平参数中：一个参数表征梯度检测的效率，另一个参数与趋化性的动态范围有关。因此，我们的方法解释了特定的信号转导特性如何影响细菌趋化性的系统水平性能。我们进一步表明，这两个参数可以从毛细管测定的已发表实验数据中得出，这成功地描述了细菌趋化性的性能。
