Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan, Republic of China.
J Bacteriol. 2012 Dec;194(23):6518-26. doi: 10.1128/JB.01228-12. Epub 2012 Sep 28.
Feo is a transport system commonly used by bacteria to acquire environmental Fe(2+). It consists of three proteins: FeoA, FeoB, and FeoC. FeoB is a large protein with a cytosolic N-terminal domain (NFeoB) that contains a regulatory G protein domain and a helical S domain. The C-terminal region of FeoB is a transmembrane domain that likely acts as the Fe(2+) permease. NFeoB has been shown to form a trimer pore that may function as an Fe(2+) gate. FeoC is a small winged-helix protein that possesses four conserved cysteine residues with a consensus sequence that likely provides binding sites for the [Fe-S] cluster. Therefore, FeoC is presumed to be an [Fe-S] cluster-dependent regulator that directly controls transcription of the feo operon. Despite the apparent significance of the Feo system, however, the function of FeoC has not been experimentally demonstrated. Here, we show that Klebsiella pneumoniae FeoC (KpFeoC) forms a tight complex with the intracellular N-terminal domain of FeoB (KpNFeoB). The crystal structure of the complex reveals that KpFeoC binds to KpNFeoB between the switch II region of the G protein domain and the effector S domain and that the long KpFeoC W1 loop lies above the KpNFeoB nucleotide-binding site. These interactions suggest that KpFeoC modulates the guanine nucleotide-mediated signal transduction process. Moreover, we showed that binding of KpFeoC disrupts pore formation by interfering with KpNFeoB trimerization. These results provide strong evidence suggesting that KpFeoC plays a crucial role in regulating Fe(2+) transport in Klebsiella pneumonia in addition to the presumed gene regulator role.
铁载体是一种细菌普遍用来获取环境中 Fe(2+)的运输系统。它由三种蛋白质组成：FeoA、FeoB 和 FeoC。FeoB 是一种具有细胞质 N 端结构域（NFeoB）的大型蛋白质，其中包含一个调节 G 蛋白结构域和一个螺旋 S 结构域。FeoB 的 C 端区域是一个跨膜结构域，可能充当 Fe(2+) 通透酶。已证明 NFeoB 形成一个可能作为 Fe(2+) 门的三聚体孔。FeoC 是一种带有四个保守半胱氨酸残基的小翼螺旋蛋白，其保守序列可能为 [Fe-S] 簇提供结合位点。因此，FeoC 被认为是一种直接控制 feo 操纵子转录的 [Fe-S] 簇依赖性调节剂。尽管铁载体系统具有明显的重要性，然而，FeoC 的功能尚未通过实验证明。在这里，我们表明肺炎克雷伯氏菌 FeoC（KpFeoC）与 FeoB 的胞内 N 端结构域（KpNFeoB）形成紧密复合物。该复合物的晶体结构揭示，KpFeoC 结合到 KpNFeoB 位于 G 蛋白结构域的开关 II 区域和效应 S 结构域之间，并且长的 KpFeoC W1 环位于 KpNFeoB 核苷酸结合位点上方。这些相互作用表明，KpFeoC 调节鸟嘌呤核苷酸介导的信号转导过程。此外，我们表明 KpFeoC 通过干扰 KpNFeoB 的三聚化来破坏孔形成，从而结合。这些结果提供了有力的证据，表明 KpFeoC 除了被认为的基因调节作用外，还在调节肺炎克雷伯氏菌中的 Fe(2+) 转运中起着关键作用。
