The structural analysis of the periplasmic domain of Sinorhizobium meliloti chemoreceptor McpZ reveals a novel fold and suggests a complex mechanism of transmembrane signaling
The structural analysis of the periplasmic domain of Sinorhizobium meliloti chemoreceptor McpZ reveals a novel fold and suggests a complex mechanism of transmembrane signaling
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DOI：
10.1002/prot.26510
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发表时间：
2023-05-22
影响因子：
2.9
通讯作者：
Schubot，Florian D. D.
中科院分区：
文献类型：
--
作者：
Salar，Safoura;Ball，Nicolas E. E.;Schubot，Florian D. D.
趋化性是细菌寻找营养源和避免有害化学物质的基本过程。苜蓿中华根瘤菌（Sinorhizobium meliloti）的趋化系统在其与豆科植物的相互作用中也起着重要的作用。趋化性信号级联通过引诱剂或驱避剂化合物与化学受体或甲基接受趋化蛋白（MCP）的相互作用启动。苜蓿草有八种化学感受器介导趋化性。这些受体中的六种是具有周质配体结合结构域（LBD）的跨膜蛋白。McpW和McpZ的具体功能尚不清楚。在这里，我们报告的晶体结构的周质域的McpZ（McpZPD）在2.7毫米分辨率。McpZPD假设由三个级联的四螺旋束模块组成的新折叠。通过系统发育分析，我们发现这种螺旋三模块结构域折叠出现在根瘤菌科中，并且仍在快速进化。该结构提供了一种罕见的无配体的二聚MCP-LBD，揭示了一种新的二聚界面。分子动力学计算表明，配体结合将诱导构象变化，导致McpZPD二聚体近膜结构域内的大的水平螺旋运动，伴随着末端螺旋向细胞内膜的5 μ m垂直位移。这些结果表明，这种MCP家族的跨膜信号传导机制需要活塞式和剪刀式运动。预测的运动终止于与在相关配体结合的MCP-LBD中观察到的构象密切相关的构象。
Chemotaxis is a fundamental process whereby bacteria seek out nutrient sources and avoid harmful chemicals. For the symbiotic soil bacteriumSinorhizobium meliloti, the chemotaxis system also plays an essential role in the interaction with its legume host. The chemotactic signaling cascade is initiated through interactions of an attractant or repellent compound with chemoreceptors or methyl‐accepting chemotaxis proteins (MCPs).S. melilotipossesses eight chemoreceptors to mediate chemotaxis. Six of these receptors are transmembrane proteins with periplasmic ligand‐binding domains (LBDs). The specific functions of McpW and McpZ are still unknown. Here, we report the crystal structure of the periplasmic domain of McpZ (McpZPD) at 2.7 Å resolution. McpZPD assumes a novel fold consisting of three concatenated four‐helix bundle modules. Through phylogenetic analyses, we discovered that this helical tri‐modular domain fold arose within the Rhizobiaceae family and is still evolving rapidly. The structure, offering a rare view of a ligand‐free dimeric MCP‐LBD, reveals a novel dimerization interface. Molecular dynamics calculations suggest ligand binding will induce conformational changes that result in large horizontal helix movements within the membrane‐proximal domains of the McpZPD dimer that are accompanied by a 5 Å vertical shift of the terminal helix toward the inner cell membrane. These results suggest a mechanism of transmembrane signaling for this family of MCPs that entails both piston‐type and scissoring movements. The predicted movements terminate in a conformation that closely mirrors those observed in related ligand‐bound MCP‐LBDs.