Department of Environmental Protection, Estación Experimental del Zaidín-Consejo Superior de Investigaciones Científicas, Granada, Spain; Section of Molecular Microbiology, Department of Molecular Cell Biology, VU University Amsterdam, Amsterdam, The Netherlands.
Environ Microbiol. 2014 Aug;16(8):2433-43. doi: 10.1111/1462-2920.12371. Epub 2014 Jan 21.
Extracytoplasmic function (ECF) sigma factors play a key role in the regulation of vital functions in the bacterial response to the environment. In Gram-negative bacteria, activity of these sigma factors is often controlled by cell-surface signalling (CSS), a regulatory system that also involves an outer membrane receptor and a transmembrane anti-sigma factor. To get more insight into the molecular mechanism behind CSS regulation, we have focused on the unique Iut system of Pseudomonas putida. This system contains a hybrid protein containing both a cytoplasmic ECF sigma domain and a periplasmic anti-sigma domain, apparently leading to a permanent interaction between the sigma and anti-sigma factor. We show that the Iut ECF sigma factor regulates the response to aerobactin under iron deficiency conditions and is activated by a proteolytic pathway that involves the sequential action of two proteases: Prc, which removes the periplasmic anti-sigma domain, and RseP, which subsequently removes the transmembrane domain and thereby generates the ECF active transcriptional form. We furthermore demonstrate the role of these proteases in the regulation of classical CSS systems in which the sigma and anti-sigma factors are two different proteins.
细胞外功能（ECF）σ因子在细菌对环境的反应中对重要功能的调节中起着关键作用。在革兰氏阴性细菌中，这些σ因子的活性通常受细胞表面信号（CSS）控制，这是一个调节系统，还涉及外膜受体和跨膜抗σ因子。为了更深入地了解 CSS 调节背后的分子机制，我们专注于假单胞菌属的独特 Iut 系统。该系统包含一种含有细胞质 ECF σ结构域和周质抗σ结构域的混合蛋白，显然导致σ因子和抗σ因子之间的永久相互作用。我们表明，Iut ECF σ因子调节缺铁条件下对铁载体的反应，并被涉及两种蛋白酶的顺序作用的蛋白水解途径激活：Prc，其去除周质抗σ结构域，然后 RseP 去除跨膜结构域，从而产生 ECF 活性转录形式。我们还证明了这些蛋白酶在调节经典 CSS 系统中的作用，其中σ因子和抗σ因子是两种不同的蛋白质。
