Purification and characterization of an extracellular heme-binding protein, HasA, involved in heme iron acquisition
Purification and characterization of an extracellular heme-binding protein, HasA, involved in heme iron acquisition
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DOI：
10.1021/bi962577s
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发表时间：
1997-06-10
期刊：
影响因子：
2.9
通讯作者：
Lecroisey, A
中科院分区：
文献类型：
--
作者：
Izadi, N;Henry, Y;Lecroisey, A
最近已分离出许多参与血红素获取的细菌血红素蛋白，包括外膜受体和细胞外血红素结合蛋白。迄今为止，这些蛋白质提取血红素的机制尚未被描述。其中一种蛋白质 HasA 可以结合游离血红素并从血红蛋白中捕获它，它是由革兰氏阴性菌粘质沙雷氏菌在缺铁条件下分泌的。 HasA 与其他已知血红素蛋白不存在序列相似性，这一事实表明它拥有一种新型血红素结合位点。这项工作描述了 HasA 的主要理化特性，这对于理解其功能至关重要。 HasA 是一种 19 kDa 的单体，每个分子以高亲和力结合一个 b 血红素。电子顺磁共振谱表明血红素铁处于低自旋三价铁态，两个铁轴向配体是His和His(-)。与 HasA 结合的血红素的低氧化还原电位值（-550 mV 相对于标准氢电极）表明血红素可能暴露于溶剂中。根据圆二色性数据，血红素的结合似乎没有改变HasA的构象。
Many bacterial hemoproteins involved in heme acquisition have been isolated recently, comprising outer membrane receptors and extracellular heme-binding protein. The mechanisms by which these proteins extract heme have not been described up to now. One such protein, HasA, which can bind free heme as well as capture it from hemoglobin, is secreted by the Gram-negative bacteria Serratia marcescens under iron deficiency conditions. The fact that HasA does not present sequence similarities with other known hemoproteins suggests that it posseses a new type of heme binding site. This work describes the main physicochemical properties of HasA, essential for understanding its function. HasA is a monomer of 19 kDa that binds one b heme per molecule with high affinity. The electron paramagnetic resonance spectra indicate that the heme iron is in a low-spin ferric state and that the two iron axial ligands are His and His(-). The low oxidation-reduction potential value (-550 mV vs standard hydrogen electrode) of the heme bound to HasA suggests that heme could be exposed to the solvent. According to circular dichroism data, the binding of heme does not seem to modify the conformation of HasA.