Sensory adaptation in bacterial chemotaxis is mediated by posttranslational modifications of methyl-accepting chemotaxis proteins (MCPs). In Escherichia coli, the adaptation proteins CheR and CheB tether to a conserved C-terminal receptor pentapeptide. Here,we investigated the function of the pentapeptide motif (N/D)WE(E/N)F in Sinorhizobium meliloti chemotaxis. Isothermal titration calorimetry revealed stronger affinity of the pentapeptides to CheR and activated CheB relative to unmodified CheB. Strains with mutations of the conserved tryptophan in one or all four MCP pentapeptides resulted in a significant decrease or loss of chemotaxis to glycine betaine, lysine, and acetate, chemoattractants sensed by pentapeptide-bearing McpX and pentapeptide-lacking McpU and McpV, respectively. Importantly, we discovered that the pentapeptide mediates chemotaxis when fused to the C-terminus of pentapeptide-lacking chemoreceptors via a flexible linker. We propose that adaptational assistance and a threshold number of available sites enable the efficient docking of adaptation proteins to the chemosensory array. Altogether, these results demonstrate that S. meliloti effectively utilizes a pentapeptide-dependent adaptation system with a minimal number of tethering units to assist pentapeptide-lacking chemoreceptors and hypothesize that the higher abundance of CheR and CheB in S. meliloti compared to E. coli allows for ample recruitment of adaptation proteins to the chemosensory array.

中文翻译：

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苜蓿中华根瘤菌中的化学感受器需要最少的五肽系链来提供适应帮助


细菌趋化中的感觉适应是由甲基接受趋化蛋白（MCP）的翻译后修饰介导的。在大肠杆菌中，适应蛋白 CheR 和 CheB 与保守的 C 末端受体五肽相连。在这里，我们研究了五肽基序(N/D)WE(E/N)F在苜蓿中华根瘤菌趋化性中的功能。等温滴定量热法显示，相对于未修饰的 CheB，五肽对 CheR 和活化的 CheB 的亲和力更强。一种或全部四种 MCP 五肽中保守色氨酸突变的菌株导致对甘氨酸甜菜碱、赖氨酸和乙酸盐的趋化性显着降低或丧失，这些趋化剂分别由带有五肽的 McpX 和缺乏五肽的 McpU 和 McpV 感知。重要的是，我们发现当五肽通过柔性连接体融合到缺乏五肽的化学感受器的C端时，会介导趋化性。我们提出，适应辅助和可用位点的阈值数量能够使适应蛋白与化学感应阵列有效对接。总而言之，这些结果表明，苜蓿中华根瘤菌有效地利用了具有最少数量束缚单元的五肽依赖性适应系统来辅助缺乏五肽的化学感受器，并假设苜蓿中华根瘤菌中的 CheR 和 CheB 丰度高于大肠杆菌，从而允许用于将适应蛋白充分招募到化学感应阵列中。