Utilization and cell-surface binding of hemin by Histoplasma capsulatum
Utilization and cell-surface binding of hemin by Histoplasma capsulatum
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DOI：
10.1139/w02-037
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发表时间：
2002-05-01
影响因子：
2.8
通讯作者：
Foster, LAA
中科院分区：
文献类型：
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作者：
Foster, LAA
荚膜组织胞浆菌是一种二形性真菌，能够在免疫功能低下的个体中引起严重的呼吸道疾病，在哺乳动物感染期间存在于巨噬细胞中。先前的研究表明，当生物体驻留在巨噬细胞中时，铁载体介导的铁转运对于从转铁蛋白获取铁可能很重要。然而，铁也以氯高铁血红素的形式存在于巨噬细胞的细胞内环境中，并且可能作为感染期间铁的主要来源。因此检查了荚膜梭菌利用血红素和含血红素的化合物的能力。通过向培养物中添加铁螯合剂甲磺酸去铁胺，使荚膜组织胞浆菌 G217B 缺铁。在甲磺酸去铁胺存在下添加 10 muM 氯高铁血红素可将生长恢复至不存在螯合剂时的水平。荚膜组织胞浆菌也在不添加螯合剂的铁限制、化学成分确定的培养基中培养，并且确定该生物体也可以使用血红蛋白作为铁的唯一来源。通过测量血红素与酵母细胞表面的结合来检查铁从血红素内化的方法。荚膜梭菌结合血红素的能力与细胞的营养状况有关。与在不含螯合剂的培养基中生长的细胞相比，在铁限制条件下生长的细胞将更多的血红素结合到细胞表面。用蛋白酶 K 预处理缺铁细胞，消除了生物体结合氯化血红素的能力。此外，将缺铁的荚膜梭菌与氯化血红素预孵育消除了这些细胞从溶液中去除氯化血红素的能力，尽管将细胞与无铁形式的氯化血红素、原卟啉IX预孵育仅适度影响生物体结合氯化血红素的能力。这些结果表明，荚膜梭菌使用血红素作为铁的唯一来源，并且铁获取的一种机制涉及血红素的细胞表面受体。
Histoplasma capsulatum, a dimorphic fungus capable of causing severe respiratory illness in immunocompromised individuals, resides in macrophages during mammalian infection. Previous studies suggest that siderophore-mediated iron transport may be important for the acquisition of iron from transferrin while the organism resides in macrophages. However, iron is also present as hemin in the intracellular environment of the macrophage and may serve as a major source of iron during infection. Thus the ability of H. capsulatum to use hemin and heme-containing compounds was examined. Histoplasma capsulatum G217B was iron-starved by adding the iron chelator deferoxamine mesylate to the culture. The addition of 10 muM hemin in the presence of deferoxamine mesylate restored growth to the levels seen in the absence of the chelator. Histoplasma capsulatum was also cultivated in an iron-limited, chemically defined medium without the addition of chelators and it was determined that the organism could also use hemoglobin as a sole source of iron. The method of iron internalization from heme was examined by measuring hemin binding to the yeast-cell surface. The ability of H. capsulatum to bind hemin was related to the nutritional status of the cells. Cells grown under iron-limited conditions bound more heme to the cell surface than did cells grown in medium without chelator. Pretreatment of iron-starved cells with proteinase K eliminated the ability of the organism to bind hemin. Additionally, the pre-incubation of iron-starved H. capsulatum with hemin eliminated the ability of these cells to remove hemin from the solution, although pre-incubation of cells with the iron-free form of hemin, protoporphyrin IX, only modestly affected the ability of the organism to bind hemin. These results suggest that H. capsulatum uses hemin as a sole source of iron and that one mechanism of iron acquisition involves a cell-surface receptor for hemin.