Collaborative signaling by mixed chemoreceptor teams in Escherichia coli
Collaborative signaling by mixed chemoreceptor teams in Escherichia coli
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DOI：
10.1073/pnas.092071899
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发表时间：
2002-05-14
影响因子：
11.1
通讯作者：
Parkinson, JS
中科院分区：
文献类型：
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作者：
Ames, P;Studdert, CA;Parkinson, JS
在细菌和古生物中，甲基趋化蛋白家族的化学受体形成簇，通常位于细胞极点(S)。为了阐明受体簇的结构和信号作用，我们研究了大肠杆菌中丝氨酸(TSR)和天冬氨酸(TAR)化学受体之间的相互作用，方法是在参与形成“二聚体三聚体”的6个疏水残基和5个极性残基上构建TSR突变。带有脯氨酸替换的TSR突变体不能介导丝氨酸趋化、受体聚集或顺时针鞭毛旋转。丙氨酸和色氨酸突变体，虽然也不趋化，但形成受体簇，一些产生顺时针方向的鞭毛旋转，表明信号Chea激酶的受体偶联激活。丙氨酸和色氨酸突变体明显地组装缺陷的受体复合体，该复合体不能调节CHEA的活性以响应丝氨酸刺激。在含有野生型TAR受体的细胞中，TSR中的色氨酸替代干扰了TAR的功能，而4个带有丙氨酸替代的TSR突变体恢复了TSR的功能。这些上位性和可挽救的表型暗示了TSR和Tar二聚体在更高级别的信号组中的相互作用。色氨酸突变体中庞大的侧链可能会阻止刺激诱导的构象变化，而丙氨酸突变体中的小侧链可能会在与功能受体分子结合时允许信号控制。通过体内化学交联观察到TSR和TAR分子之间的直接物理相互作用。野生型TSR与Tar发生交联，而簇缺陷的Pro替换突变体则没有。这些发现表明，细菌化学感受器簇由似乎基于二聚体三聚体的信号团队组成，这些信号团队包含不同类型的受体协同作用。
Chemoreceptors of the methyl-accepting chemotaxis protein family form clusters, typically at the cell pole(s), in both Bacteria and Archaea. To elucidate the architecture and signaling role of receptor clusters, we investigated interactions between the serine (Tsr) and aspartate (Tar) chemoreceptors in Escherichia coli by constructing Tsr mutations at the six hydrophobic and five polar residues implicated in "trimer of dimers" formation. Tsr mutants with proline replacements could not mediate serine chemotaxis, receptor clustering, or clockwise flagellar rotation. Alanine and tryptophan mutants, although also nonchemotactic, formed receptor clusters, and some produced clockwise flagellar rotation, indicating receptor-coupled activation of the signaling CheA kinase. The alanine and tryptophan mutants evidently assemble defective receptor complexes that cannot modulate CheA activity in response to serine stimuli. In cells containing wild-type Tar receptors, tryptophan replacements in Tsr interfered with Tar function, whereas four Tsr mutants with alanine replacements regained Tsr function. These epistatic and rescuable phenotypes imply interactions between Tsr and Tar dimers in higher-order signaling teams. The bulky side chain in tryptophan mutants may prevent stimulus-induced conformational changes in the team, whereas the small side chain in alanine mutants may permit signaling control when teamed with functional receptor molecules. Direct physical interactions between Tsr and Tar molecules were observed by in vivo chemical crosslinking. Wild-type Tsr crosslinked to Tar, whereas a clustering-defective proline replacement mutant did not. These findings indicate that bacterial chemoreceptor clusters are comprised of signaling teams, seemingly based on trimers of dimers, that ran contain different receptor types acting collaboratively.