Pilpa Rosemarie M, Robson Scott A, Villareal Valerie A, Wong Melissa L, Phillips Martin, Clubb Robert T
Department of Chemistry and Biochemistry, UCLA-DOE Institute for Genomics and Proteomics, UCLA, Los Angeles, California 90095, USA.
J Biol Chem. 2009 Jan 9;284(2):1166-76. doi: 10.1074/jbc.M806007200. Epub 2008 Nov 3.
The pathogen Staphylococcus aureus uses iron-regulated surface determinant (Isd) proteins to scavenge the essential nutrient iron from host hemoproteins. The IsdH protein (also known as HarA) is a receptor for hemoglobin (Hb), haptoglobin (Hp), and the Hb-Hp complex. It contains three NEAT (NEAr Transporter) domains: IsdH(N1), IsdH(N2), and IsdH(N3). Here we show that they have different functions; IsdH(N1) binds Hb and Hp, whereas IsdH(N3) captures heme that is released from Hb. The staphylococcal IsdB protein also functions as an Hb receptor. Primary sequence homology to IsdH indicates that it will also employ functionally distinct NEAT domains to bind heme and Hb. We have used site-directed mutagenesis and surface plasmon resonance methods to localize the Hp and Hb binding surface on IsdH(N1). High affinity binding to these structurally unrelated proteins requires residues located within a conserved aromatic motif that is positioned at the end of the beta-barrel structure. Interestingly, this site is quite malleable, as other NEAT domains use it to bind heme. We also demonstrate that the IsdC NEAT domain can capture heme directly from Hb, suggesting that there are multiple pathways for heme transfer across the cell wall.
病原菌金黄色葡萄球菌利用铁调节表面决定簇（Isd）蛋白从宿主血红蛋白中获取必需营养物质铁。IsdH蛋白（也称为HarA）是血红蛋白（Hb）、触珠蛋白（Hp）以及Hb-Hp复合物的受体。它包含三个NEAT（近转运体）结构域：IsdH(N1)、IsdH(N2)和IsdH(N3)。在此我们表明它们具有不同功能；IsdH(N1)结合Hb和Hp，而IsdH(N3)捕获从Hb释放的血红素。葡萄球菌IsdB蛋白也作为Hb受体发挥作用。与IsdH的一级序列同源性表明它也将利用功能不同的NEAT结构域来结合血红素和Hb。我们已使用定点突变和表面等离子体共振方法来定位IsdH(N1)上的Hp和Hb结合表面。与这些结构不相关蛋白的高亲和力结合需要位于β桶状结构末端保守芳香基序内的残基。有趣的是，这个位点相当具有可塑性，因为其他NEAT结构域利用它来结合血红素。我们还证明IsdC NEAT结构域可以直接从Hb捕获血红素，这表明存在多条血红素跨细胞壁转移的途径。
