Department of Biochemistry, 117 Schweitzer Hall, University of Missouri-Columbia, Columbia, MO 65211, USA.
J Bacteriol. 2010 Mar;192(5):1193-200. doi: 10.1128/JB.01391-09. Epub 2010 Jan 8.
Transmembrane chemoreceptors are central components in bacterial chemotaxis. Receptors couple ligand binding and adaptational modification to receptor conformation in processes that create transmembrane signaling. Homodimers, the fundamental receptor structural units, associate in trimers and localize in patches of thousands. To what degree do conformational coupling and transmembrane signaling require higher-order interactions among dimers? To what degree are they altered by such interactions? To what degree are they inherent features of homodimers? We addressed these questions using nanodiscs to create membrane environments in which receptor dimers had few or no potential interaction partners. Receptors with many, few, or no interaction partners were tested for conformational changes and transmembrane signaling in response to ligand occupancy and adaptational modification. Conformation was assayed by measuring initial rates of receptor methylation, a parameter independent of receptor-receptor interactions. Coupling of ligand occupancy and adaptational modification to receptor conformation and thus to transmembrane signaling occurred with essentially the same sensitivity and magnitude in isolated dimers as for dimers with many neighbors. Thus, we conclude that the chemoreceptor dimer is the fundamental unit of conformational coupling and transmembrane signaling. This implies that in signaling complexes, coupling and transmembrane signaling occur through individual dimers and that changes between dimers in a receptor trimer or among trimer-based signaling complexes are subsequent steps in signaling.
跨膜化学感受器是细菌趋化作用的核心组成部分。在将配体结合和适应性修饰与受体构象偶联的过程中，受体创建了跨膜信号转导。同源二聚体是基本的受体结构单元，以三聚体的形式结合，并在数千个斑块中定位。构象偶联和跨膜信号转导在多大程度上需要二聚体之间的高级别相互作用？这些相互作用在多大程度上改变了它们？它们在多大程度上是同源二聚体的固有特征？我们使用纳米盘来创建膜环境，在该环境中二聚体几乎没有或没有潜在的相互作用伙伴，从而解决了这些问题。我们测试了具有许多、很少或没有相互作用伙伴的受体，以检测其在配体占据和适应性修饰时的构象变化和跨膜信号转导。构象通过测量受体甲基化的初始速率来检测，这是一个独立于受体-受体相互作用的参数。配体占据和适应性修饰与受体构象的偶联，从而与跨膜信号转导的偶联，在孤立的二聚体中和在具有许多相邻二聚体的二聚体中，其敏感性和幅度基本相同。因此，我们得出结论，化学感受器二聚体是构象偶联和跨膜信号转导的基本单元。这意味着在信号复合物中，偶联和跨膜信号转导通过单个二聚体发生，并且受体三聚体或基于三聚体的信号复合物中二聚体之间的变化是信号传递的后续步骤。
