Stauff Devin L, Torres Victor J, Skaar Eric P
Department of Microbiology and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA.
J Biol Chem. 2007 Sep 7;282(36):26111-21. doi: 10.1074/jbc.M703797200. Epub 2007 Jul 16.
For the important human pathogen Staphylococcus aureus, host heme is a vital source of nutrient iron during infection. Paradoxically, heme is also toxic at high concentrations and is capable of killing S. aureus. To maintain cellular heme homeostasis, S. aureus employs the coordinated actions of the heme sensing two-component system (HssRS) and the heme regulated transporter efflux pump (HrtAB). HssRS-dependent expression of HrtAB results in the alleviation of heme toxicity and tempered staphylococcal virulence. Although genetic experiments have defined the role of HssRS in the heme-dependent activation of hrtAB, the mechanism of this activation is not known. Furthermore, the global effect of HssRS on S. aureus gene expression has not been evaluated. Herein, we combine multivariable difference gel electrophoresis with mass spectrometry to identify the heme-induced cytoplasmic HssRS regulon. These experiments establish hrtAB as the major target of activation by HssRS in S. aureus. In addition, we show that signaling between the sensor histidine kinase HssS and the response regulator HssR is necessary for growth of S. aureus in high concentrations of heme. Finally, we show that a direct repeat DNA sequence within the hrtAB promoter is required for heme-induced, HssR-dependent expression driven by this promoter and that phosphorylated HssR binds to this direct repeat upon exposure of S. aureus to high concentrations of heme. Taken together, these data establish the mechanism for HssRS-dependent expression of HrtAB and, in turn, provide a functional understanding for how S. aureus avoids heme-mediated toxicity.
对于重要的人类病原体金黄色葡萄球菌而言，宿主血红素是感染期间营养性铁的重要来源。矛盾的是，血红素在高浓度时也是有毒的，能够杀死金黄色葡萄球菌。为维持细胞血红素稳态，金黄色葡萄球菌利用血红素感应双组分系统（HssRS）和血红素调节转运体流出泵（HrtAB）的协同作用。HrtAB依赖HssRS的表达可减轻血红素毒性并减弱葡萄球菌的毒力。尽管遗传学实验已明确HssRS在hrtAB血红素依赖性激活中的作用，但这种激活的机制尚不清楚。此外，尚未评估HssRS对金黄色葡萄球菌基因表达的整体影响。在此，我们将多变量差异凝胶电泳与质谱相结合，以鉴定血红素诱导的细胞质HssRS调控子。这些实验确定hrtAB是金黄色葡萄球菌中HssRS激活的主要靶点。此外，我们表明传感器组氨酸激酶HssS与反应调节因子HssR之间的信号传导对于金黄色葡萄球菌在高浓度血红素中的生长是必需的。最后，我们表明hrtAB启动子内的一个直接重复DNA序列是该启动子驱动的血红素诱导的、依赖HssR的表达所必需的，并且在金黄色葡萄球菌暴露于高浓度血红素时，磷酸化的HssR会结合到这个直接重复序列上。综上所述，这些数据确立了HrtAB依赖HssRS表达的机制，进而为金黄色葡萄球菌如何避免血红素介导的毒性提供了功能上的理解。
