Center for Advanced Biotechnology and Medicine, Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, 679 Hoes Lane West, Piscataway, NJ 08854, USA.
J Mol Biol. 2013 May 27;425(10):1612-26. doi: 10.1016/j.jmb.2013.02.003. Epub 2013 Feb 8.
The OmpR/PhoB family of response regulators (RRs) is the largest class of two-component system signal transduction proteins. Extensive biochemical and structural characterization of these transcription factors has provided insights into their activation and DNA-binding mechanisms. For the most part, OmpR/PhoB family proteins are thought to become activated through phosphorylation from their cognate histidine kinase partners, which in turn facilitates an allosteric change in the RR, enabling homodimerization and subsequently enhanced DNA binding. Incongruently, it has been suggested that OmpR, the eponymous member of this RR family, becomes activated via different mechanisms, whereby DNA binding plays a central role in facilitating dimerization and phosphorylation. Characterization of the rate and extent of the phosphorylation of OmpR and OmpR DNA-binding mutants following activation of the EnvZ/OmpR two-component system shows that DNA binding is not essential for phosphorylation of OmpR in vivo. In addition, detailed analyses of the energetics of DNA binding and dimerization of OmpR in both its unphosphorylated and phosphorylated state indicate that phosphorylation enhances OmpR dimerization and that this dimerization enhancement is the energetic driving force for phosphorylation-mediated regulation of OmpR-DNA binding. These findings suggest that OmpR phosphorylation-mediated activation follows the same paradigm as the other members of the OmpR/PhoB family of RRs in contrast to previously proposed models of OmpR activation.
OmpR/PhoB 家族的反应调节蛋白 (RRs) 是双组分系统信号转导蛋白中最大的一类。对这些转录因子的广泛生化和结构特征分析为其激活和 DNA 结合机制提供了深入了解。在大多数情况下，OmpR/PhoB 家族蛋白被认为通过其同源组氨酸激酶伴侣的磷酸化而被激活，这反过来又促进 RR 的变构，从而实现同源二聚化并随后增强 DNA 结合。不一致的是，有人提出 OmpR（该 RR 家族的同名成员）通过不同的机制被激活，其中 DNA 结合在促进二聚化和磷酸化方面起着核心作用。对 EnvZ/OmpR 双组分系统激活后 OmpR 和 OmpR DNA 结合突变体的磷酸化速率和程度的表征表明，DNA 结合对于体内 OmpR 的磷酸化不是必需的。此外，对 OmpR 在其未磷酸化和磷酸化状态下的 DNA 结合和二聚化的能量学的详细分析表明，磷酸化增强了 OmpR 的二聚化，并且这种二聚化增强是磷酸化介导的 OmpR-DNA 结合调控的能量驱动力。这些发现表明，OmpR 磷酸化介导的激活遵循与 OmpR/PhoB 家族的其他 RR 成员相同的范例，与之前提出的 OmpR 激活模型相反。
