Biology Centre, Institute of Parasitology, Czech Academy of Sciences and Faculty of Science, University of South Bohemia, 370 05 České Budějovice, Czech Republic.
Proc Natl Acad Sci U S A. 2012 Mar 6;109(10):3808-13. doi: 10.1073/pnas.1201089109. Epub 2012 Feb 21.
Heme is an iron-coordinated porphyrin that is universally essential as a protein cofactor for fundamental cellular processes, such as electron transport in the respiratory chain, oxidative stress response, or redox reactions in various metabolic pathways. Parasitic kinetoplastid flagellates represent a rare example of organisms that depend on oxidative metabolism but are heme auxotrophs. Here, we show that heme is fully dispensable for the survival of Phytomonas serpens, a plant parasite. Seeking to understand the metabolism of this heme-free eukaryote, we searched for heme-containing proteins in its de novo sequenced genome and examined several cellular processes for which heme has so far been considered indispensable. We found that P. serpens lacks most of the known hemoproteins and does not require heme for electron transport in the respiratory chain, protection against oxidative stress, or desaturation of fatty acids. Although heme is still required for the synthesis of ergosterol, its precursor, lanosterol, is instead incorporated into the membranes of P. serpens grown in the absence of heme. In conclusion, P. serpens is a flagellate with unique metabolic adaptations that allow it to bypass all requirements for heme.
血红素是一种铁配位的卟啉，作为一种蛋白质辅因子，普遍存在于基本的细胞过程中，如呼吸链中的电子传递、氧化应激反应或各种代谢途径中的氧化还原反应。寄生的动基体鞭毛虫代表了一种罕见的生物体，它们依赖氧化代谢，但却是血红素营养缺陷型。在这里，我们表明血红素对植物寄生虫 Phytomonas serpens 的生存是完全可有可无的。为了了解这种不含血红素的真核生物的代谢，我们在其从头测序的基因组中寻找含血红素的蛋白质，并检查了迄今为止被认为对血红素不可或缺的几个细胞过程。我们发现 P. serpens 缺乏大多数已知的血红素蛋白，并且不需要血红素来进行呼吸链中的电子传递、抵御氧化应激或脂肪酸去饱和。尽管血红素仍然是合成麦角固醇所必需的，但它的前体，羊毛甾醇，在没有血红素的情况下被掺入到 P. serpens 的膜中。总之，P. serpens 是一种具有独特代谢适应性的鞭毛虫，能够绕过对血红素的所有需求。
