Department of Biochemistry, Kansas State University, Manhattan, KS 66506, USA.
Proc Natl Acad Sci U S A. 2012 Aug 14;109(33):13337-42. doi: 10.1073/pnas.1208703109. Epub 2012 Jul 30.
Multicopper ferroxidases catalyze the oxidation of ferrous iron to ferric iron. In yeast and algae, they participate in cellular uptake of iron; in mammals, they facilitate cellular efflux. The mechanisms of iron metabolism in insects are still poorly understood, and insect multicopper ferroxidases have not been identified. In this paper, we present evidence that Drosophila melanogaster multicopper oxidase-1 (MCO1) is a functional ferroxidase. We identified candidate iron-binding residues in the MCO1 sequence and found that purified recombinant MCO1 oxidizes ferrous iron. An association between MCO1 function and iron homeostasis was confirmed by two observations: RNAi-mediated knockdown of MCO1 resulted in decreased iron accumulation in midguts and whole insects, and weak knockdown increased the longevity of flies fed a toxic concentration of iron. Strong knockdown of MCO1 resulted in pupal lethality, indicating that MCO1 is an essential gene. Immunohistochemistry experiments demonstrated that MCO1 is located on the basal surfaces of the digestive system and Malpighian tubules. We propose that MCO1 oxidizes ferrous iron in the hemolymph and that the resulting ferric iron is bound by transferrin or melanotransferrin, leading to iron storage, iron withholding from pathogens, regulation of oxidative stress, and/or epithelial maturation. These proposed functions are distinct from those of other known ferroxidases. Given that MCO1 orthologues are present in all insect genomes analyzed to date, this discovery is an important step toward understanding iron metabolism in insects.
多铜氧化酶催化二价铁氧化为三价铁。在酵母和藻类中，它们参与细胞对铁的摄取；在哺乳动物中，它们促进细胞铁的外排。昆虫的铁代谢机制仍知之甚少，昆虫的多铜氧化酶也尚未被鉴定。本文我们提出证据表明果蝇多铜氧化酶-1（MCO1）是一种功能性的亚铁氧化酶。我们鉴定了 MCO1 序列中的候选铁结合残基，并发现纯化的重组 MCO1 能氧化二价铁。MCO1 功能与铁稳态之间的联系通过两个观察结果得到证实：RNAi 介导的 MCO1 敲低导致中肠和整只昆虫铁积累减少，而弱敲低则增加了摄入有毒浓度铁的果蝇的寿命。MCO1 的强敲低导致蛹死亡，表明 MCO1 是必需基因。免疫组织化学实验表明 MCO1 位于消化系统和马氏管的基底表面。我们提出 MCO1 氧化血淋巴中的二价铁，生成的三价铁被转铁蛋白或黑素转铁蛋白结合，从而导致铁储存、阻止铁进入病原体、调节氧化应激和/或上皮成熟。这些提出的功能与其他已知的亚铁氧化酶不同。鉴于迄今分析的所有昆虫基因组中都存在 MCO1 同源物，这一发现是理解昆虫铁代谢的重要一步。
