Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana 47405, USA.
J Biol Chem. 2012 Apr 20;287(17):13850-8. doi: 10.1074/jbc.M112.346494. Epub 2012 Feb 29.
Heme-mediated regulation, presented in many biological processes, is achieved in part with proteins containing heme regulatory motif. In this study, we demonstrate that FLAG-tagged PpsR isolated from Rhodobacter sphaeroides cells contains bound heme. In vitro heme binding studies with tagless apo-PpsR show that PpsR binds heme at a near one-to-one ratio with a micromolar binding constant. Mutational and spectral assays suggest that both the second Per-Arnt-Sim (PAS) and DNA binding domains of PpsR are involved in the heme binding. Furthermore, we show that heme changes the DNA binding patterns of PpsR and induces different responses of photosystem genes expression. Thus, PpsR functions as both a redox and heme sensor to coordinate the amount of heme, bacteriochlorophyll, and photosystem apoprotein synthesis thereby providing fine tune control to avoid excess free tetrapyrrole accumulation.
血红素介导的调节存在于许多生物过程中，部分是通过含有血红素调节基序的蛋白质来实现的。在这项研究中，我们证明了从球形红杆菌细胞中分离的带有 FLAG 标签的 PpsR 含有结合的血红素。用无标签的脱辅基 apo-PpsR 进行体外血红素结合研究表明，PpsR 以近一比一的比例与微摩尔结合常数结合血红素。突变和光谱分析表明，PpsR 的第二个 Per-Arnt-Sim（PAS）和 DNA 结合结构域都参与了血红素结合。此外，我们还表明，血红素改变了 PpsR 的 DNA 结合模式，并诱导了光合系统基因表达的不同反应。因此，PpsR 作为一种氧化还原和血红素传感器，调节血红素、细菌叶绿素和光合系统脱辅基蛋白的合成量，从而提供精细的调控，以避免过量的游离四吡咯积累。
