部分革兰氏阴性菌胞外功能sigma因子结构与调控铁离子的利用机制

The Structure and Regulation of ECF Sigma Factor in Iron Acquisition of Some Gram-negative Bacteria

铁离子是大多数细菌生存所必需的一种营养物质,但摄入过多的铁离子也会对细菌造成损伤。因此,细菌对铁离子的摄取受到严格调控。革兰氏阴性菌对铁离子的摄取主要受Fur(ferric uptake regulator)蛋白和σ(sigma)因子的调控。σ因子是RNA聚合酶的可解离亚基,能使RNA聚合酶结合到基因的启动子区域,从而引起基因转录。因此,σ因子在原核生物转录起始过程中必不可少。细菌中存在多种σ因子,参与铁离子调控的σ因子即是胞外功能σ因子(extra-cytoplasmic function sigma factor,ECF sigma factor)。通常,胞外功能σ因子活性可被抗σ因子(anti-sigma factor)抑制。当受到外界环境信号的刺激,σ因子与抗σ因子解离,从而使σ因子活化并结合RNA聚合酶核心酶形成全酶,引起目的基因的转录。本文将就胞外功能σ因子在σ因子家族中的分类地位、结构特点以及对3价铁离子和血红素的转运调控机制作一综述。

Iron is an essential nutrient for the most of bacteria. However, excessive iron is also potential toxic to the bacteria. Therefore, iron levels within the cell are tightly regulated. For most bacteria, iron uptake is regulated by fur （ferric up-take regulator） protein. Additionally, iron uptake is also regulated by sigma factors. Sigma factors are subunits of the RNA polymerase, which was able to bind to the respective promoter recognition sites. Hence, sigma factors are essential for prokaryotic transcription initiation. Bacteria harbor many kinds of sigma factors. Among them, the sigma factors involved in iron regulation were called extracytoplasmic function （ECF） sigma factors. Usually. ECF sigma factor was inactive, since it was bound by anti-sigma factors. When bacteria is subject to stimulation of appropriate environmental signals, ECF sigma factor will be released and interact with core RNA polymerase to form holo-enzyme, thereby resulting in transcription of target genes. This review described the taxonomic status and structure features of ECF sigma factors as well as its regulation mechanism in iron and heine utilization in some gram-negative bacteria.