金黄色葡萄球菌是健康个体皮肤和鼻孔的常见定植剂,也是人类严重感染的主要原因。在与主机交互期间,病原菌必须适应各种不利条件,包括营养剥夺。特别是,它们通过触珠蛋白和铁结合蛋白的铁螯合在哺乳动物宿主中遇到严重的铁限制,一种叫做“营养免疫”的现象。“在大多数细菌中,包括金黄色葡萄球菌,铁摄取调节剂(Fur)是铁稳态的关键调节剂,主要充当编码铁获取系统的基因的转录阻遏子。此外,Fur可以控制反式作用小调节RNA的表达,这些RNA在铁限制条件下涉及细胞代谢的主要变化的细胞铁保护反应中起重要作用。在金黄色葡萄球菌中,sRNAIsrR由Fur控制,其预测的大多数目标是含铁蛋白质和其他与铁代谢和铁依赖性途径相关的蛋白质。为了在全基因组范围内表征IsrR靶组,我们使用缺乏或组成型表达IsrR的金黄色葡萄球菌菌株,结合了基于蛋白质组学的潜在IsrR靶标鉴定与计算机靶标预测方法,从而暗示了21个IsrR目标,根据观察到的蛋白质模式,其中19受到IsrR的负面影响。其中包括几种含Fe-S簇和血红素的蛋白质,如KatA编码的TCA循环酶和过氧化氢酶。IsrR影响与TCA循环相关的多种代谢途径以及金黄色葡萄球菌的氧化应激反应,并将铁限制反应与代谢重塑联系起来。与大多数靶mRNA相反,IsrR-katAmRNA相互作用被预测在核糖体结合位点的上游,包括mRNA半衰期测量在内的进一步实验表明,IsrR,除了抑制翻译启动,可以通过影响mRNA稳定性下调靶蛋白水平。
Staphylococcus aureus is a common colonizer of the skin and nares of healthy individuals, but also a major cause of severe human infections. During interaction with the host, pathogenic bacteria must adapt to a variety of adverse conditions including nutrient deprivation. In particular, they encounter severe iron limitation in the mammalian host through iron sequestration by haptoglobin and iron-binding proteins, a phenomenon called \"nutritional immunity.\" In most bacteria, including S. aureus, the ferric uptake regulator (Fur) is the key regulator of iron homeostasis, which primarily acts as a transcriptional repressor of genes encoding iron acquisition systems. Moreover, Fur can control the expression of trans-acting small regulatory RNAs that play an important role in the cellular iron-sparing response involving major changes in cellular metabolism under iron-limiting conditions. In S. aureus, the sRNA
IsrR is controlled by Fur, and most of its predicted targets are iron-containing proteins and other proteins related to iron metabolism and iron-dependent pathways. To characterize the
IsrR targetome on a genome-wide scale, we combined proteomics-based identification of potential
IsrR targets using S. aureus strains either lacking or constitutively expressing
IsrR with an in silico target prediction approach, thereby suggesting 21 IsrR targets, of which 19 were negatively affected by
IsrR based on the observed protein patterns. These included several Fe-S cluster- and heme-containing proteins, such as TCA cycle enzymes and catalase encoded by katA. IsrR affects multiple metabolic pathways connected to the TCA cycle as well as the oxidative stress response of S. aureus and links the iron limitation response to metabolic remodeling. In contrast to the majority of target mRNAs, the
IsrR-katA mRNA interaction is predicted upstream of the ribosome binding site, and further experiments including mRNA half-life measurements demonstrated that IsrR, in addition to inhibiting translation initiation, can downregulate target protein levels by affecting mRNA stability.