Distinct Domains of CheA Confer Unique Functions in Chemotaxis and Cell Length in Azospirillum brasilense Sp7
Distinct Domains of CheA Confer Unique Functions in Chemotaxis and Cell Length in Azospirillum brasilense Sp7
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DOI：
10.1128/jb.00189-17
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发表时间：
2017-07-01
影响因子：
3.2
通讯作者：
Alexandre, Gladys
中科院分区：
文献类型：
--
作者：
Gullett, Jessica M.;Bible, Amber;Alexandre, Gladys
趋化性是细胞响应不同化学信号梯度的运动。运动细菌利用保守的趋化信号转导系统来偏置它们的运动并通过梯度导航。趋化性的核心调节因子是组氨酸激酶 CheA。这种细胞质蛋白与膜结合受体相互作用，后者组装成大型极性阵列，以传播信号。在巴西固氮螺菌α变形菌中，Che1控制趋化过程中游动速度的短暂增加，但它也会使分裂时的细胞长度产生偏差。然而，Che1 依赖性控制多种细胞行为的确切潜在分子机制尚不清楚。在这里，我们确定了参与调节这些功能的 CheA1 组氨酸激酶的特定结构域。我们发现 CheA1 产生两种同种型：一种是膜锚定同种型，是与 N 端功能未知的保守七跨膜结构域 (TMX) 融合而产生的，另一种是与原型 CheA 类似的可溶性同种型。定点突变和缺失突变与行为分析相结合，证实了 CheA1 在趋化性中的作用，并表明 TMX 结构域在介导细胞长度变化中发挥着重要作用。荧光显微镜进一步揭示膜锚定亚型分布在细胞表面周围，而可溶性亚型位于细胞两极。总之，这些数据提供了一种机制，说明 Che1 通过获取 CheA1 中的新结构域并产生不同的功能亚型来控制多种不相关的细胞行为。 重要性 趋化性为环境中的细菌提供了显着的竞争优势，并且该功能已横向转移多次，有证据表明不同基因组环境中存在功能差异。在不同基因组背景下趋化功能多样化的分子原理尚不清楚。在这里，我们提供了一种分子机制，单个 CheA 蛋白通过该机制控制两个不相关的功能：趋化性和细胞长度。这种多功能性的获得似乎是最近的一个进化事件。这些发现说明了一种机制，通过该机制可以选择趋化功能来调节其他细胞功能。
Chemotaxis is the movement of cells in response to gradients of diverse chemical cues. Motile bacteria utilize a conserved chemotaxis signal transduction system to bias their motility and navigate through a gradient. A central regulator of chemotaxis is the histidine kinase CheA. This cytoplasmic protein interacts with membrane-bound receptors, which assemble into large polar arrays, to propagate the signal. In the alphaproteobacterium Azospirillum brasilense, Che1 controls transient increases in swimming speed during chemotaxis, but it also biases the cell length at division. However, the exact underlying molecular mechanisms for Che1-dependent control of multiple cellular behaviors are not known. Here, we identify specific domains of the CheA1 histidine kinase implicated in modulating each of these functions. We show that CheA1 is produced in two isoforms: a membraneanchored isoform produced as a fusion with a conserved seven-transmembrane domain of unknown function (TMX) at the N terminus and a soluble isoform similar to prototypical CheA. Site-directed and deletion mutagenesis combined with behavioral assays confirm the role of CheA1 in chemotaxis and implicate the TMX domain in mediating changes in cell length. Fluorescence microscopy further reveals that the membrane-anchored isoform is distributed around the cell surface while the soluble isoform localizes at the cell poles. Together, the data provide a mechanism for the role of Che1 in controlling multiple unrelated cellular behaviors via acquisition of a new domain in CheA1 and production of distinct functional isoforms.IMPORTANCE Chemotaxis provides a significant competitive advantage to bacteria in the environment, and this function has been transferred laterally multiple times, with evidence of functional divergence in different genomic contexts. The molecular principles that underlie functional diversification of chemotaxis in various genomic contexts are unknown. Here, we provide a molecular mechanism by which a single CheA protein controls two unrelated functions: chemotaxis and cell length. Acquisition of this multifunctionality is seemingly a recent evolutionary event. The findings illustrate a mechanism by which chemotaxis function may be co-opted to regulate additional cellular functions.