Laboratoiro de Estudios Cristalográficos, Instituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas (CSIC)-Universidad de Granada, 18100 Armilla-Granada, Spain.
Proc Natl Acad Sci U S A. 2012 Nov 13;109(46):18926-31. doi: 10.1073/pnas.1201400109. Epub 2012 Oct 29.
Chemoreceptor-based signaling is a central mechanism in bacterial signal transduction. Receptors are classified according to the size of their ligand-binding region. The well-studied cluster I proteins have a 100- to 150-residue ligand-binding region that contains a single site for chemoattractant recognition. Cluster II receptors, which contain a 220- to 300-residue ligand-binding region and which are almost as abundant as cluster I receptors, remain largely uncharacterized. Here, we report high-resolution structures of the ligand-binding region of the cluster II McpS chemotaxis receptor (McpS-LBR) of Pseudomonas putida KT2440 in complex with different chemoattractants. The structure of McpS-LBR represents a small-molecule binding domain composed of two modules, each able to bind different signal molecules. Malate and succinate were found to bind to the membrane-proximal module, whereas acetate binds to the membrane-distal module. A structural alignment of the two modules revealed that the ligand-binding sites could be superimposed and that amino acids involved in ligand recognition are conserved in both binding sites. Ligand binding to both modules was shown to trigger chemotactic responses. Further analysis showed that McpS-like receptors were found in different classes of proteobacteria, indicating that this mode of response to different carbon sources may be universally distributed. The physiological relevance of the McpS architecture may lie in its capacity to respond with high sensitivity to the preferred carbon sources malate and succinate and, at the same time, mediate lower sensitivity responses to the less preferred but very abundant carbon source acetate.
基于化学感受器的信号转导是细菌信号转导的核心机制。受体根据其配体结合区域的大小进行分类。经过充分研究的第一类簇蛋白具有 100-150 个残基的配体结合区域，其中包含一个用于化学引诱剂识别的单一位点。第二类簇受体的配体结合区域含有 220-300 个残基，与第一类簇受体一样丰富，但仍在很大程度上未被表征。在这里，我们报告了 Pseudomonas putida KT2440 的第二类簇 McpS 趋化性受体（McpS-LBR）的配体结合区域与不同化学引诱剂复合物的高分辨率结构。McpS-LBR 的结构代表了由两个模块组成的小分子结合域，每个模块都能够结合不同的信号分子。发现苹果酸和琥珀酸结合在膜近端模块上，而乙酸结合在膜远端模块上。两个模块的结构比对表明，配体结合位点可以叠加，并且参与配体识别的氨基酸在两个结合位点中是保守的。配体与两个模块的结合都被证明可以引发趋化反应。进一步的分析表明，McpS 样受体存在于不同类别的变形菌中，这表明这种对不同碳源的反应模式可能普遍存在。McpS 结构的生理相关性可能在于它能够对首选碳源苹果酸和琥珀酸产生高灵敏度的响应，同时对不太受欢迎但非常丰富的碳源乙酸进行较低灵敏度的响应。
