Iron is essential for nearly all aerobic organisms. One source of iron in nature is in the form of heme. Due to its critical physiological importance as a cofactor for several enzymes, organisms have evolved various means to secure heme for their needs. In the case of heme prototrophs, these organisms possess a highly conserved eight-step biosynthetic pathway. Another means used by many organisms is to acquire heme from external sources. As opposed to the knowledge of enzymes responsible for heme biosynthesis, the nature of the players and mechanisms involved in the acquisition of exogenous heme is limited. This review focuses on a description of newly discovered proteins that have novel functions in heme assimilation in the model organism Schizosaccharomyces pombe. This tractable model allows the use of the power of genetics to selectively block heme biosynthesis, setting conditions to investigate the mechanisms by which external heme is taken up by the cells. Studies have revealed that S. pombe possesses two independent heme uptake systems that require Shu1 and Str3, respectively. Heme-bound iron is captured by Shu1 at the cell surface, triggering its internalization to the vacuole with the aid of ubiquitinated proteins and the ESCRT machinery. In the case of the plasma membrane transporter Str3, it promotes cellular heme import in cells lacking Shu1. The discovery of these two pathways may contribute to gain novel insights into the mechanisms whereby fungi assimilate heme, which is an essentially biological process for their ability to invade and colonize new niches.

铁对几乎所有有氧生物都是必不可少的。自然界中铁的一种来源是血红素。由于其作为几种酶的辅助因子的至关重要的生理重要性，生物体已进化出各种方法来确保血红素满足其需求。就血红素原养生物而言，这些生物具有高度保守的八步生物合成途径。许多生物使用的另一种方法是从外部来源获取血红素。与负责血红素生物合成的酶的知识相反，参与获取外源血红素的参与者和机制的性质是有限的。这篇综述的重点是描述在模型生物Schizosaccharomyces pombe中具有新的在血红素吸收中具有新功能的蛋白质。这种易于处理的模型允许利用遗传学的力量选择性阻断血红素的生物合成，为研究细胞吸收外部血红素的机制设置条件。研究表明，粟酒裂殖酵母拥有两个独立的血红素摄取系统，分别需要Shu1和Str3。血红素结合的铁被Shu1捕获在细胞表面，借助泛素化蛋白和ESCRT机制触发其内化至液泡。就质膜转运蛋白Str3而言，它促进缺乏Shu1的细胞中血红素的导入。这两种途径的发现可能有助于获得对真菌吸收血红素的机制的新颖见解，而血红素是入侵和定居新能力的基本生物学过程。