Finding the way: Sensory adaptation during bacterial mechanotransduction

摘要 感觉适应是一个短期记忆过程，通过这个过程，信号系统返回到其 尽管持续暴露于输入信号，但仍保持刺激前水平。尽管在 细菌的趋化性，很少有人知道如何适应在其他细菌的信号运作 系统.更好地了解适应如何在这些系统中运作将提供新的 基础知识，并可以确定新的治疗方法。我们专注于 机械传感，这是表面定殖和感染假单胞菌的关键 铜绿假单胞菌（PA）是多重耐药医院感染的主要原因， 健康威胁。PA使用Pil-Chp机械传感系统来识别机械信号， 驱动抽搐运动和cAMP产生，以调节表面上的毒力程序 contact.适应如何在这个系统中发挥作用，或者说一般的机械感知，还没有被探索过。 我们建议剖析Pil-Chp系统中适应的机制和作用，因为（i） 机械感觉适应系统的核心酶机制，甲基化 酶PilK和去甲基化酶ChpB是保守的，但其调节似乎是 与E.大肠杆菌趋化系统;（ii）该系统提供了了解 如何部署适应以应对地表接触;以及（iii）Pil-Chp系统 在急性肺炎的鼠模型中有助于毒力，证明其与 人PA感染。我们发现PilK作为甲基化酶，ChpB作为甲基化酶。 PilJ化学感受器的脱甲基酶来控制两个输出。与趋化性不同， 甲基化酶和去甲基化酶表现出相反的空间定位。我们的研究支持一个模型， PilK甲基化酶定位于后极，PilJ化学感受器将位于后极 甲基化并准备被激活。相比之下，ChpB脱甲基酶被募集到 通过与响应调节器PilG的相互作用来引导极点。需要PilG进行协调 TFP在前极的伸展和收缩。这种定位将导致时间和 在前导极点处的空间限制的PilJ去甲基化。PilJ的活动会受到抑制， 潜在地促进PilG重新定位到滞后极点和反转。因此，感官 Pil-Chp系统中的适应与E.大肠趋化性 因为它使用时间和空间线索。我们将测试这个假设如下：目标1.链路 PilJ甲基化与PilJ活性和输出有关。目标2.确定响应如何 调节因子PilG调节ChpB脱甲基酶。目标3。测试PilK甲基化酶是否 由MapZ（一种c-di-GMP结合蛋白）调节，以连接抽搐和鞭毛运动。

Abstract Sensory adaptation is a short-term memory process by which a signaling system returns to its pre-stimulus level despite ongoing exposure to the input signal. Although well-characterized in bacterial chemotaxis, little is known about how adaptation operates in the other bacterial signaling systems. A better understanding of how adaptation operates in these systems will provide new fundamental knowledge and could identify new therapeutic approaches. We focus on mechanosensing, which is critical for surface colonization and infection in Pseudomonas aeruginosa (PA), a leading cause of multi-drug resistant nosocomial infections and a significant health threat. PA uses the Pil-Chp mechanosensing system to transduce a mechanical signal that drives twitching motility and cAMP production to modulate a virulence program upon surface contact. How adaptation functions in this system, or mechanosensing in general, is unexplored. We propose to dissect the mechanism and role of adaptation in the Pil-Chp system because (i) The core enzymatic machinery of the mechanosensory adaptation system, the methylating enzyme PilK and demethylating enzyme ChpB, are conserved but its regulation appears to be distinct from the E. coli chemotaxis system; (ii) This system affords the opportunity to understand how adaptation is deployed in response to surface contact; and (iii) The Pil-Chp system contributes to virulence in a murine model of acute pneumonia, demonstrating its relevance to human PA infections. We discovered that PilK acts as a methylase and ChpB acts as a demethylase for the PilJ chemoreceptor to control the two outputs. Unlike in chemotaxis, the methylase and demethylase exhibit inverse spatial localization. Our studies support a model in which the PilK methylase localizes to the lagging pole, where the PilJ chemoreceptor would be methylated and poised to be activated. In contrast, the ChpB demethylase is recruited to the leading pole by interactions with the response regulator PilG. PilG is required for coordinating TFP extension and retraction at the leading pole. This localization would lead to temporally and spatially restricted PilJ demethylation at the leading pole. PilJ activity would be dampened, potentially facilitating PilG relocalization to the lagging pole and reversals. Thus, sensory adaptation in the Pil-Chp system is fundamentally different from adaptation in E. coli chemotaxis in that it uses temporal AND spatial cues. We will test this hypothesis as follows: Aim 1. Link PilJ methylation states to PilJ activity and outputs. Aim 2. Determine how the response regulator PilG regulates the ChpB demethylase. Aim 3. Test whether the PilK methylase is regulated by MapZ, a c-di-GMP binding protein, to link twitching and flagellar motility.