Cheng Zhuo, Li Keran, Hammad Loubna A, Karty Jonathan A, Bauer Carl E
Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, IN, 47405, USA.
Mol Microbiol. 2014 Feb;91(4):649-64. doi: 10.1111/mmi.12491. Epub 2014 Jan 9.
The tetrapyrroles haem, bacteriochlorophyll and cobalamin (B12 ) exhibit a complex interrelationship regarding their synthesis. In this study, we demonstrate that AerR functions as an antirepressor of the tetrapyrrole regulator CrtJ. We show that purified AerR contains B12 that is bound to a conserved histidine (His145) in AerR. The interaction of AerR to CrtJ was further demonstrated in vitro by pull down experiments using AerR as bait and quantified using microscale thermophoresis. DNase I DNA footprint assays show that AerR containing B12 inhibits CrtJ binding to the bchC promoter. We further show that bchC expression is greatly repressed in a B12 auxotroph of Rhodobacter capsulatus and that B12 regulation of gene expression is mediated by AerR's ability to function as an antirepressor of CrtJ. This study thus provides a mechanism for how the essential tetrapyrrole, cobalamin controls the synthesis of bacteriochlorophyll, an essential component of the photosystem.
四吡咯血红素、细菌叶绿素和钴胺素（维生素B12）在其合成方面表现出复杂的相互关系。在本研究中，我们证明AerR作为四吡咯调节因子CrtJ的抗阻遏物发挥作用。我们发现纯化的AerR含有与AerR中保守组氨酸（His145）结合的维生素B12。通过以AerR为诱饵的下拉实验在体外进一步证明了AerR与CrtJ的相互作用，并使用微量热泳法进行了定量。DNase I DNA足迹分析表明，含有维生素B12的AerR抑制CrtJ与bchC启动子的结合。我们进一步表明，在荚膜红细菌的维生素B12营养缺陷型中，bchC表达受到极大抑制，并且维生素B12对基因表达的调控是由AerR作为CrtJ抗阻遏物的功能介导的。因此，本研究提供了一种机制，解释了必需四吡咯钴胺素如何控制细菌叶绿素（光系统的必需成分）的合成。
