Biology Department, University of Utah, Salt Lake City, UT 84112, USA.
J Bacteriol. 2011 Dec;193(23):6597-604. doi: 10.1128/JB.05987-11. Epub 2011 Sep 30.
The four transmembrane chemoreceptors of Escherichia coli sense phenol as either an attractant (Tar) or a repellent (Tap, Trg, and Tsr). In this study, we investigated the Tar determinants that mediate its attractant response to phenol and the Tsr determinants that mediate its repellent response to phenol. Tar molecules with lesions in the aspartate-binding pocket of the periplasmic domain, with a foreign periplasmic domain (from Tsr or from several Pseudomonas chemoreceptors), or lacking nearly the entire periplasmic domain still mediated attractant responses to phenol. Similarly, Tar molecules with the cytoplasmic methylation and kinase control domains of Tsr still sensed phenol as an attractant. Additional hybrid receptors with signaling elements from both Tar and Tsr indicated that the transmembrane (TM) helices and HAMP domain determined the sign of the phenol-sensing response. Several amino acid replacements in the HAMP domain of Tsr, particularly attractant-mimic signaling lesions at residue E248, converted Tsr to an attractant sensor of phenol. These findings suggest that phenol may elicit chemotactic responses by diffusing into the cytoplasmic membrane and perturbing the structural stability or position of the TM bundle helices, in conjunction with structural input from the HAMP domain. We conclude that behavioral responses to phenol, and perhaps to temperature, cytoplasmic pH, and glycerol, as well, occur through a general sensing mechanism in chemoreceptors that detects changes in the structural stability or dynamic behavior of a receptor signaling element. The structurally sensitive target for phenol is probably the TM bundle, but other behaviors could target other receptor elements.
大肠杆菌的四个跨膜化学感受器感知苯酚为吸引剂（Tar）或排斥剂（Tap、Trg 和 Tsr）。在这项研究中，我们研究了介导 Tar 对苯酚的吸引反应的决定因素，以及介导 Tsr 对苯酚的排斥反应的决定因素。在 Tar 分子的周质域的天冬氨酸结合口袋中有损伤、有外来的周质域（来自 Tsr 或几个假单胞菌的化学感受器）、或几乎缺乏整个周质域的 Tar 分子仍介导对苯酚的吸引反应。同样，具有 Tsr 的细胞质甲基化和激酶控制结构域的 Tar 分子仍然感知苯酚为吸引剂。来自 Tar 和 Tsr 的信号元件的额外混合受体表明，跨膜（TM）螺旋和 HAMP 结构域决定了苯酚感应反应的信号。Tsr 的 HAMP 结构域中的几个氨基酸替换，特别是在残基 E248 处的吸引剂模拟信号损伤，将 Tsr 转化为苯酚的吸引剂传感器。这些发现表明，苯酚可能通过扩散到细胞质膜并扰乱 TM 束螺旋的结构稳定性或位置，与 HAMP 结构域的结构输入一起，引发趋化反应。我们得出结论，对苯酚以及对温度、细胞质 pH 和甘油的行为反应可能通过化学感受器中的一般感应机制发生，该机制检测受体信号元件的结构稳定性或动态行为的变化。苯酚的结构敏感靶标可能是 TM 束，但其他行为可能针对其他受体元件。
