From the Liver Diseases Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-1800, USA.
J Biol Chem. 2013 Jun 14;288(24):17791-802. doi: 10.1074/jbc.M113.460253. Epub 2013 May 2.
The mechanisms through which iron-dependent enzymes receive their metal cofactors are largely unknown. Poly r(C)-binding protein 1 (PCBP1) is an iron chaperone for ferritin; both PCBP1 and its paralog PCBP2 are required for iron delivery to the prolyl hydroxylase that regulates HIF1. Here we show that PCBP2 is also an iron chaperone for ferritin. Co-expression of PCBP2 and human ferritins in yeast activated the iron deficiency response and increased iron deposition into ferritin. Depletion of PCBP2 in Huh7 cells diminished iron incorporation into ferritin. Both PCBP1 and PCBP2 were co-immunoprecipitated with ferritin in HEK293 cells, and expression of both PCBPs was required for ferritin complex formation in cells. PCBP1 and -2 exhibited high affinity binding to ferritin in vitro. Mammalian genomes encode 4 PCBPs, including the minimally expressed PCBPs 3 and 4. Expression of PCBP3 and -4 in yeast activated the iron deficiency response, but only PCBP3 exhibited strong interactions with ferritin. Expression of PCBP1 and ferritin in an iron-sensitive, ccc1 yeast strain intensified the toxic effects of iron, whereas expression of PCBP4 protected the cells from iron toxicity. Thus, PCBP1 and -2 form a complex for iron delivery to ferritin, and all PCBPs may share iron chaperone activity.
铁依赖性酶获得其金属辅因子的机制在很大程度上是未知的。多聚 r(C)结合蛋白 1 (PCBP1) 是铁蛋白的铁伴侣；PCBP1 和其同源物 PCBP2 都需要向脯氨酰羟化酶输送铁，后者调节 HIF1。本文中，我们显示 PCBP2 也是铁蛋白的铁伴侣。PCBP2 与人类铁蛋白在酵母中的共表达激活了铁缺乏反应并增加了铁向铁蛋白的沉积。在 Huh7 细胞中耗尽 PCBP2 会减少铁向铁蛋白的掺入。PCBP1 和 PCBP2 都与 HEK293 细胞中的铁蛋白共免疫沉淀，并且两种 PCBP 的表达都是细胞中铁蛋白复合物形成所必需的。PCBP1 和 -2 在体外与铁蛋白表现出高亲和力结合。哺乳动物基因组编码 4 种 PCBP，包括表达水平最低的 PCBP3 和 -4。PCBP3 和 -4 在酵母中的表达激活了铁缺乏反应，但只有 PCBP3 与铁蛋白表现出强烈的相互作用。PCBP1 和铁蛋白在铁敏感的 ccc1 酵母菌株中的表达加剧了铁的毒性作用，而 PCBP4 的表达则保护细胞免受铁毒性。因此，PCBP1 和 -2 形成复合物将铁递送至铁蛋白，并且所有 PCBP 可能都具有铁伴侣活性。
