Department of Genomic and Proteomic, Instituto de Biomedicina de Valencia (IBV-CSIC), Jaume Roig 11, 46010, Valencia, Spain.
Departamento de Bioquímica, Universitat de València, Dr Moliner 50, 46100, Burjassot, Spain.
Sci Rep. 2017 Jun 2;7(1):2708. doi: 10.1038/s41598-017-02900-z.
Microbial colonization of different environments is enabled to a great extent by the plasticity of their sensory mechanisms, among them, the two-component signal transduction systems (TCS). Here, an example of TCS plasticity is presented: the regulation of L-malate catabolism via malic enzyme by MaeRK in Lactobacillales. MaeKR belongs to the citrate family of TCS as the Escherichia coli DcuSR system. We show that the Lactobacillus casei histidine-kinase MaeK is defective in autophosphorylation activity as it lacks a functional catalytic and ATP binding domain. The cognate response regulator MaeR was poorly phosphorylated at its phosphoacceptor Asp in vitro. This phosphorylation, however, enhanced MaeR binding in vitro to its target sites and it was required for induction of regulated genes in vivo. Elucidation of the MaeR structure revealed that response regulator dimerization is accomplished by the swapping of α4-β5-α5 elements between two monomers, generating a phosphoacceptor competent conformation. Sequence and phylogenetic analyses showed that the MaeKR peculiarities are not exclusive to L. casei as they are shared by the rest of orthologous systems of Lactobacillales. Our results reveal MaeKR as a non-canonical TCS displaying distinctive features: a swapped response regulator and a sensor histidine kinase lacking ATP-dependent kinase activity.
不同环境中的微生物定植在很大程度上取决于其感觉机制的可塑性，其中包括双组分信号转导系统（TCS）。这里介绍了 TCS 可塑性的一个例子：通过 MaeRK 在乳杆菌目中调节苹果酸酶的 L-苹果酸分解代谢。MaeKR 属于 TCS 的柠檬酸家族，就像大肠杆菌 DcuSR 系统一样。我们表明，由于缺乏功能催化和 ATP 结合域，乳酸乳球菌组氨酸激酶 MaeK 在自身磷酸化活性方面存在缺陷。在体外，天冬氨酸残基磷酸化的效应物调节剂 MaeR 磷酸化程度很差。然而，这种磷酸化增强了 MaeR 与靶位的结合，并且对于体内调节基因的诱导是必需的。阐明 MaeR 的结构表明，响应调节剂二聚体通过两个单体之间的α4-β5-α5 元件的交换来完成，从而产生磷酸化接受体功能的构象。序列和系统发育分析表明，MaeKR 的特殊性不仅限于 L. casei，因为它们也存在于乳杆菌目其余的同源系统中。我们的研究结果揭示了 MaeKR 作为一种非典型 TCS 具有独特的特征：交换的响应调节剂和缺乏 ATP 依赖性激酶活性的传感器组氨酸激酶。
