Ragland M, Briat J F, Gagnon J, Laulhere J P, Massenet O, Theil E C
Department of Biochemistry, North Carolina State University, Raleigh 27695-7622.
J Biol Chem. 1990 Oct 25;265(30):18339-44.
Ferritin is a large multisubunit protein that stores iron in plants, animals, and bacteria. In animals, the protein is mainly cytoplasmic and is highly conserved, while in plants ferritin is found in chloroplasts and other plastids. Ferritin is synthesized in plants as a larger precursor of the mature subunit. There is no sequence information for ferritin from plants, except an NH2-terminal peptide of 35 residues which shows little similarity to any known ferritin sequences or transit peptides (Laulhere, J. P., Laboure, A. M., and Briat, J. F. (1989) J. Biol. Chem. 264, 3629-3635). To understand the genetic origin and the location of ferritin synthesis in plant cells, as well as the structure of ferritin from plants, we have sequenced both CNBr peptides from pea seed ferritin and nucleotides of a soybean hypocotyl ferritin cDNA, identified using a frog ferritin cDNA as a probe. Comparison of pea and soybean sequences showed an identity of 89%. Alignment of the plant ferritin sequences with animal ferritins showed 55-65% sequence identity in the common regions. However, a peptide of 28 amino acids extended the NH2 terminus of the plant ferritins. Furthermore, the cDNA encoded additional amino acids which appear to be a transit peptide. None of the sequences in soybean ferritin were found in the tobacco chloroplast genome, suggesting, as does the transit peptide, a nuclear location of ferritin gene(s) in plants. Plant ferritin mRNA is 400-500 nucleotides longer than animal ferritin mRNAs, a difference accounted for in part by the extra peptides encoded. The size of soybean ferritin mRNA was constant in different tissues but expression varied in different tissues (leaf greater than hypocotyl). Thus, higher plants and animal ferritins display sequence homology and differential tissue expression. An ancient, common progenitor apparently gave rise to contemporary eukaryotic ferritins after specific modifications, e.g. transport to plasmids.
铁蛋白是一种大型多亚基蛋白，在植物、动物和细菌中储存铁。在动物中，该蛋白主要存在于细胞质中且高度保守，而在植物中，铁蛋白存在于叶绿体和其他质体中。植物中的铁蛋白是作为成熟亚基的更大前体合成的。除了一个35个残基的NH2末端肽外，没有来自植物铁蛋白的序列信息，该肽与任何已知的铁蛋白序列或转运肽几乎没有相似性（劳勒尔，J.P.，拉布尔，A.M.，和布里亚特，J.F.（1989年）《生物化学杂志》264，3629 - 3635）。为了了解植物细胞中铁蛋白的遗传起源、合成位置以及植物铁蛋白的结构，我们对豌豆种子铁蛋白的两个溴化氰肽段以及大豆下胚轴铁蛋白cDNA的核苷酸进行了测序，该cDNA是用青蛙铁蛋白cDNA作为探针鉴定出来的。豌豆和大豆序列的比较显示同一性为89%。植物铁蛋白序列与动物铁蛋白序列的比对显示，在共同区域序列同一性为55 - 65%。然而，一个28个氨基酸的肽段延伸了植物铁蛋白的NH2末端。此外，cDNA编码了额外的氨基酸，这些氨基酸似乎是一个转运肽。在烟草叶绿体基因组中未发现大豆铁蛋白中的任何序列，这与转运肽一样，表明植物中铁蛋白基因位于细胞核中。植物铁蛋白mRNA比动物铁蛋白mRNA长400 - 500个核苷酸，这种差异部分是由编码的额外肽段造成的。大豆铁蛋白mRNA的大小在不同组织中是恒定的，但在不同组织中的表达有所不同（叶片大于下胚轴）。因此，高等植物和动物铁蛋白显示出序列同源性和不同的组织表达。一个古老的共同祖先显然在经过特定修饰（例如转运到质体）后产生了当代真核生物铁蛋白。
