ABSTRACT Iron is one of the most abundant elements on Earth, and it is essential for life. Despite the abundance of iron, its chemistry leads to very limited bioavailability, which has resulted in the evolution of a wide range of proteins involved in uptake and scavenging. However, because high intracellular concentrations of iron are toxic, iron homeostasis is essential for every organism. Approximately 30–40% of the ocean’s surface is characterized by very low chlorophyll concentrations and high concentrations of nitrate and phosphate. These High Nutrient-Low Chlorophyll (HNLC) regions are also characterized by low concentrations of iron, and studies on low-iron adapted diatom strains revealed the presence of iron starvation-induced proteins (ISIP), a group of unrelated novel proteins that are strongly up-regulated under iron limitation. First functional characterizations show that some of these ISIP proteins are involved in iron uptake. Here, we compare iron-uptake/storage proteins from 15 different algal species demonstrating that some well-characterized uptake proteins such as Natural Resistance Associated Macrophage Proteins (NRAMP) or the iron transporter1 (FTR1)-like permease show high similarities throughout the 15 algal species, while others such as Zinc-Regulated Transporter (ZRT)- and Iron-Regulated Transporter (IRT)-like proteins (ZIP) have a higher diversity amongst the algae analysed here. The focus of this review is ISIP proteins, which are distinct from ZIP, NRAMP and FTR1 permeases. ISIP2 proteins are transferrin-like proteins involved in Fe3+ uptake and ISIP1 is responsible for endocytosis of siderophore-bound iron. Additionally, in-silico analysis, combined with our localization study in a marine diatom, suggests that ISIP3 acts as an iron storage protein. Overall, our analysis concludes that marine algae combine iron uptake strategies widespread in other organisms, with algal-specific ISIPs as additional proteins for the utilization of diverse iron pools, thereby securing their success in iron-poor regions.

中文翻译：

---

藻类中的铁吸收蛋白和铁饥饿诱导蛋白 (ISIP) 的作用

摘要 铁是地球上最丰富的元素之一，对生命至关重要。尽管铁含量丰富，但其化学性质导致生物利用度非常有限，这导致了大量参与摄取和清除的蛋白质的进化。然而，因为细胞内高浓度的铁是有毒的，所以铁稳态对每个生物都是必不可少的。大约 30-40% 的海洋表面的特点是叶绿素浓度非常低，而硝酸盐和磷酸盐浓度很高。这些高营养-低叶绿素 (HNLC) 区域的特征还在于铁浓度低，对低铁适应硅藻菌株的研究表明存在铁饥饿诱导蛋白 (ISIP)，这是一组不相关的新型蛋白质在铁限制下上调。第一个功能特征表明这些 ISIP 蛋白中的一些与铁吸收有关。在这里，我们比较了 15 种不同藻类的铁吸收/储存蛋白，证明一些特征明确的吸收蛋白，如天然抗性相关巨噬细胞蛋白 (NRAMP) 或铁转运蛋白 1 (FTR1) 样通透酶在 15 种藻类中表现出高度相似性物种，而其他如锌调节转运蛋白 (ZRT) 和铁调节转运蛋白 (IRT) 样蛋白 (ZIP) 在此处分析的藻类中具有更高的多样性。本综述的重点是 ISIP 蛋白，它们不同于 ZIP、NRAMP 和 FTR1 通透酶。ISIP2 蛋白是参与 Fe3+ 摄取的转铁蛋白样蛋白，ISIP1 负责铁载体结合铁的内吞作用。此外，在硅片分析中，结合我们在海洋硅藻中的定位研究，表明 ISIP3 充当铁储存蛋白。总体而言，我们的分析得出的结论是，海藻将其他生物中普遍存在的铁吸收策略与藻类特异性 ISIP 作为额外蛋白质结合使用，以利用不同的铁库，从而确保它们在缺铁地区取得成功。