Protein Connectivity in Chemotaxis Receptor Complexes.
Protein Connectivity in Chemotaxis Receptor Complexes.
复制标题
DOI：
10.1371/journal.pcbi.1004650
复制
发表时间：
2015-12
影响因子：
4.3
通讯作者：
Endres RG
中科院分区：
文献类型：
--
作者：
Eismann S;Endres RG
趋化性感觉系统允许细菌如大肠杆菌游向营养物并远离驱虫剂。潜在的途径是非常敏感的检测化学梯度在很大范围内的环境浓度。主要聚集在细胞两极的受体之间的相互作用对这种敏感性至关重要。虽然已经表明激酶CheA和接头蛋白CheW对于受体连接是不可或缺的，但确切的偶联机制仍不清楚。在这里，我们提出了一个螺旋力学方法来模拟受体连接机制本身，建立在纳米盘和电子冷冻断层扫描实验。具体而言，我们调查的混合受体簇的传感行为是如何受到影响的变化的表达水平的CheA和CheW在一个恒定的受体密度在膜上。我们的模型与体内Förster共振能量转移（FRET）测量的剂量-反应曲线相比毫不逊色，表明受体甲基化水平对受体协同性只有很小的影响。重要的是，我们的模型为非直观的结论提供了解释，即受体协同性随着与受体相关的核心信号蛋白CheA水平的增加而降低，而受体协同性随着关键衔接蛋白CheW水平的增加而增加。最后，我们提出了一个进化的优势，解释最近建议咀嚼只有连接器结构。细菌趋化性感觉系统的受体簇充当天线，放大细胞化学环境中浓度的微小变化，最终引导细胞朝向营养物并远离毒素。尽管细菌趋化性是最广泛研究的感觉通路，受体簇的确切结构仍然是推测性的，理解遭受了一些矛盾的观察。为了解决这些问题，在连接受体的连接器中的蛋白质排列，我们提出了一个冷冻力学模型，结合电子冷冻断层扫描的连接器结构的见解与活细胞中信号的荧光成像的结果。虽然在连接器中的关键分子组分的不同表达水平的信号数据似乎在第一矛盾，我们的模型调和这些预测与结构和生化数据。最后，我们提供了一个进化的解释的观察，一些纳入连接器似乎不从受体传递信号。
The chemotaxis sensory system allows bacteria such as Escherichia coli to swim towards nutrients and away from repellents. The underlying pathway is remarkably sensitive in detecting chemical gradients over a wide range of ambient concentrations. Interactions among receptors, which are predominantly clustered at the cell poles, are crucial to this sensitivity. Although it has been suggested that the kinase CheA and the adapter protein CheW are integral for receptor connectivity, the exact coupling mechanism remains unclear. Here, we present a statistical-mechanics approach to model the receptor linkage mechanism itself, building on nanodisc and electron cryotomography experiments. Specifically, we investigate how the sensing behavior of mixed receptor clusters is affected by variations in the expression levels of CheA and CheW at a constant receptor density in the membrane. Our model compares favorably with dose-response curves from in vivo Förster resonance energy transfer (FRET) measurements, demonstrating that the receptor-methylation level has only minor effects on receptor cooperativity. Importantly, our model provides an explanation for the non-intuitive conclusion that the receptor cooperativity decreases with increasing levels of CheA, a core signaling protein associated with the receptors, whereas the receptor cooperativity increases with increasing levels of CheW, a key adapter protein. Finally, we propose an evolutionary advantage as explanation for the recently suggested CheW-only linker structures. Receptor clusters of the bacterial chemotaxis sensory system act as antennae to amplify tiny changes in concentrations in the chemical environment of the cell, ultimately steering the cell towards nutrients and away from toxins. Despite bacterial chemotaxis being the most widely studied sensory pathway, the exact architecture of the receptor clusters remains speculative, with understanding suffering from a number of paradoxical observations. To address these issues with respect to the protein arrangement in the linkers connecting receptors, we present a statistical-mechanics model that combines insights from electron cryotomography on the linker architecture with results from fluorescence imaging of signaling in living cells. Although the signaling data for different expression levels of key molecular components in the linkers seems contradictory at first, our model reconciles these predictions with structural and biochemical data. Finally, we provide an evolutionary explanation for the observation that some of the incorporated linkers do not seem to transmit signals from the receptors.