Instituto de Biología Molecular y Celular de Rosario (IBR-CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, 2000 Rosario, Argentina.
Biochemistry. 2010 Apr 13;49(14):3161-7. doi: 10.1021/bi100136n.
The FapR protein of Bacillus subtilis has been shown to play an important role in membrane lipid homeostasis. FapR acts as a repressor of many genes involved in fatty acid and phospholipid metabolism (the fap regulon). FapR binding to DNA is antagonized by malonyl-CoA, and thus FapR acts as a sensor of the status of fatty acid biosynthesis. However, malonyl-CoA is utilized for fatty acid synthesis only following its conversion to malonyl-ACP, which plays a central role in the initiation and elongation cycles carried out by the type II fatty acid synthase. Using in vitro transcription studies and isothermal titration calorimetry, we show here that malonyl-ACP binds FapR, disrupting the repressor-operator complex with an affinity similar to that of its precursor malonyl-CoA. NMR experiments reveal that there is no protein-protein recognition between ACP and FapR. These findings are consistent with the crystal structure of malonyl-ACP, which shows that the malonyl-phosphopantetheine moiety protrudes away from the protein core and thus can act as an effector ligand. Therefore, FapR regulates the expression of the fap regulon in response to the composition of the malonyl-phosphopantetheine pool. This mechanism ensures that fatty acid biosynthesis in B. subtilis is finely regulated at the transcriptional level by sensing the concentrations of the two first intermediates (malonyl-CoA and malonyl-ACP) in order to balance the production of membrane phospholipids.
枯草芽孢杆菌的 FapR 蛋白被证明在膜脂动态平衡中发挥重要作用。FapR 作为许多参与脂肪酸和磷脂代谢的基因（fap 调控子）的抑制剂发挥作用。FapR 与 DNA 的结合受到丙二酰辅酶 A 的拮抗，因此 FapR 作为脂肪酸合成状态的传感器发挥作用。然而，只有在丙二酰-CoA 转化为丙二酰-ACP 后，丙二酰-CoA 才被用于脂肪酸合成，丙二酰-ACP 在由 II 型脂肪酸合酶进行的起始和延伸循环中发挥核心作用。通过体外转录研究和等温滴定量热法，我们在这里表明丙二酰-ACP 结合 FapR，通过与其前体丙二酰-CoA 相似的亲和力破坏抑制物-操纵子复合物。NMR 实验表明 ACP 和 FapR 之间没有蛋白质-蛋白质识别。这些发现与丙二酰-ACP 的晶体结构一致，该结构表明丙二酰-磷酸泛酰巯基乙胺部分从蛋白质核心伸出，因此可以作为效应配体发挥作用。因此，FapR 调节 fap 调控子的表达，以响应丙二酰-磷酸泛酰巯基乙胺池的组成。这种机制确保了枯草芽孢杆菌中脂肪酸生物合成在转录水平上受到精细调节，通过感知两种前体（丙二酰-CoA 和丙二酰-ACP）的浓度来平衡膜磷脂的产生。
