Heme acquisition by hemophores
Heme acquisition by hemophores
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DOI：
10.1007/s10534-006-9050-y
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发表时间：
2007-06-01
期刊：
影响因子：
3.5
通讯作者：
Biville, F.
中科院分区：
文献类型：
--
作者：
Cescau, S.;Cwerman, H.;Biville, F.
细菌血球分泌到细胞外介质中，在那里它们从各种血红素蛋白中清除血红素，因为它们对这种化合物有更高的亲和力，并将其返回到它们特定的外膜受体。HasR是HasA血细胞的外膜受体，具有多种功能，需要不同的能量水平。血红素与不含或负载血红素的血球的结合是能量不依赖的。血红素从全息血细胞到外膜受体的转移也不依赖于能量。相比之下，血红素的运输和血球的释放分别需要基础或高水平的TonB和质子动力。此外，HASR是信号级联的一个组成部分，通过聚集在HAS操纵子上的基因编码的特定西格玛和抗西格玛因子来调节HAS操纵子的表达。信号是在血球以脱脂形式存在的情况下，血红素降落在HASR上。到目前为止，HAS系统是唯一具有特征的系统，在该系统中，反西格玛因子被提交给与靶操纵子相同的信号级联。HAS系统的特殊自动调节与毛皮蛋白的负调节相结合，使细菌能够适应可用的铁源。在含有血红素的血细胞中，不活跃的抗Sigma因子会积累起来，一旦血红素来源枯竭，就会被激活。因此，HAS系统不像其他受西格玛反西格玛因子调节的系统那样接受扩增，而是通过血红素可获得性触发的脉冲发挥作用。
Bacterial hemophores are secreted to the extracellular medium, where they scavenge heme from various hemoproteins due to their higher affinity for this compound, and return it to their specific outer membrane receptor. HasR, the outer membrane receptor of the HasA hemophore, assumes multiple functions which require various energy levels. Binding of heme and, of heme-free or heme-loaded hemophores is energy-independent. Heme transfer from the holo-hemophore to the outer membrane receptor is also energy-independent. In contrast, heme transport and hemophore release require basal or high levels of TonB and proton motive force, respectively. In addition, HasR is a component of a signaling cascade, regulating expression of the has operon via specific sigma and anti-sigma factors encoded by genes clustered at the has operon. The signal is the heme landing on HasR in the presence of the hemophore in its apo form. The has system is the only system thus far characterized in which the anti-sigma factor is submitted to the same signaling cascade as the target operon. Specific autoregulation of the has system, combined with negative regulation by the Fur protein, permits bacterial adaptation to the available iron source. In the presence of a heme-loaded hemophore, inactive anti-sigma factor is accumulated and can be activated as soon as the heme source dries up. Hence, the has system, instead of being submitted to amplification like other systems regulated by sigma anti-sigma factors, functions by pulses triggered by heme availability.