Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan.
Department of Frontier Bioscience, Hosei University, Koganei, Tokyo, Japan.
J Bacteriol. 2019 Apr 9;201(9). doi: 10.1128/JB.00779-18. Print 2019 May 1.
Bacteria sense environmental chemicals using chemosensor proteins, most of which are present in the cytoplasmic membrane. Canonical chemoreceptors bind their specific ligands in their periplasmic domain, and the ligand binding creates a molecular stimulus that is transmitted into the cytoplasm, leading to various cellular responses, such as chemotaxis and specific gene expression. , the causative agent of cholera, contains about 44 putative sensor proteins, which are homologous to methyl-accepting chemotaxis proteins involved in chemotaxis. Two of them, Mlp24 and Mlp37, have been identified as chemoreceptors that mediate chemotactic responses to various amino acids. Although most of the residues of Mlp37 involved in ligand binding are conserved in Mlp24, these chemoreceptors bind the same ligands with different affinities. Moreover, they have distinct cellular roles. Here we determined a series of ligand complex structures of the periplasmic domains of Mlp24 (Mlp24p). The structures revealed that Ca binds to the loop that forms the upper wall of the ligand-binding pocket. Ca does not bind to the corresponding loop of Mlp37, implying that the structural difference of the loop may cause the ligand affinity difference. Isothermal titration calorimetry (ITC) measurements indicated that Ca changes the ligand binding affinity of Mlp24p. Furthermore, Ca affected chemotactic behaviors to various amino acids mediated by Mlp24. Thus, Ca is suggested to serve as a cosignal for the primary signal mediated by Mlp24p, and fine-tunes its chemotactic behavior depending on the Ca concentration by modulating the ligand sensitivity of Mlp24. Mlp24 and Mlp37 are homologous chemoreceptors of that bind various amino acids. Although most of the residues involved in ligand interaction are conserved, these chemoreceptors show different affinities for the same ligand and play different cellular roles. A series of ligand complex structures of the periplasmic region of Mlp24 (Mlp24p) and following ITC analysis revealed that Ca binds to the loop of Mlp24p and modulates the ligand binding affinity of Mlp24p. Moreover, Ca changes the chemotactic behaviors mediated by Mlp24. We propose that Ca acts as a cosignal that modulates the affinity of Mlp24 for the primary signal, thereby changing the chemotactic behavior of .
细菌利用化学感受器蛋白感知环境中的化学物质，这些化学感受器蛋白大多存在于细胞质膜中。经典的化学感受器在其周质域结合其特定的配体，配体结合产生的分子刺激被传递到细胞质中，导致各种细胞反应，如趋化作用和特定基因的表达。霍乱弧菌含有大约 44 个假定的传感器蛋白，这些蛋白与参与趋化作用的甲基受体趋化蛋白同源。其中两种，Mlp24 和 Mlp37，已被鉴定为介导向各种氨基酸的趋化反应的化学感受器。虽然 Mlp37 中参与配体结合的大多数残基在 Mlp24 中保守，但这些化学感受器以不同的亲和力结合相同的配体。此外，它们具有不同的细胞作用。在这里，我们确定了一系列 Mlp24（Mlp24p）周质域的配体复合物结构。这些结构表明 Ca 结合到形成配体结合口袋上壁的环上。Ca 不会结合到 Mlp37 的相应环上，这表明环的结构差异可能导致配体亲和力的差异。等温滴定量热法（ITC）测量表明，Ca 改变了 Mlp24p 的配体结合亲和力。此外，Ca 影响了由 Mlp24 介导的各种氨基酸的趋化行为。因此，Ca 被认为是 Mlp24p 介导的主要信号的辅助信号，并通过调节 Mlp24 的配体敏感性来根据 Ca 浓度微调其趋化行为。Mlp24 和 Mlp37 是霍乱弧菌的同源化学感受器，它们结合各种氨基酸。尽管参与配体相互作用的大多数残基都保守，但这些化学感受器对相同的配体表现出不同的亲和力，并且发挥不同的细胞作用。一系列 Mlp24（Mlp24p）的周质区配体复合物结构及其随后的 ITC 分析表明，Ca 结合到 Mlp24p 的环上并调节 Mlp24p 的配体结合亲和力。此外，Ca 改变了由 Mlp24 介导的趋化行为。我们提出，Ca 作为一种辅助信号，调节 Mlp24 对主要信号的亲和力，从而改变霍乱弧菌的趋化行为。
