Belouchi A, Cellier M, Kwan T, Saini H S, Leroux G, Gros P
Department of Biochemistry, McGill University, Montréal, Québec, Canada.
Plant Mol Biol. 1995 Dec;29(6):1181-96. doi: 10.1007/BF00020461.
In mice, natural resistance or susceptibility to infection with Mycobacteria, Salmonella, and Leishmania is controlled by a gene named Bcg. Bcg regulates the capacity of macrophages to limit intracellular replication of the ingested parasites, and is believed to regulate a key bactericidal mechanism of this cell. Recently, we have cloned the Bcg gene and shown that it encodes a novel macrophage-specific membrane protein designated Nramp. A routine search of the public databases for sequences homologous to Nramp identified 3 expressed sequence tags (EST) that show strong similarities to the mammalian protein. We report the identification and cloning of a full-length cDNA clone corresponding to a plant homologue (OsNramp1) of mammalian Nramp. Predicted amino acid sequence of the plant protein indicates a remarkable degree of similarity (60% homology) with its mammalian counterpart, including identical number, position, and composition of transmembrane domains, glycosylation signals, and consensus transport motif, suggesting an identical overall secondary structure and membrane organization for the two proteins. This high degree of structural similarity indicates that the two proteins may be functionally related, possibly through a common mechanism of transport. RNA hybridization studies and RT-PCR analyses indicate that OsNramp1 mRNA is expressed primarily in roots and only at very low levels in leaves/stem. DNA hybridization studies indicate that OsNramp1 is not a single gene, but rather forms part of a novel gene family which has several members in all plants tested including cereals such as rice, wheat, and corn, and also in common weed species. The striking degree of conservation between the macrophage-specific mammalian Nramp and its OsNramp1 plant homologue is discussed with respect to possible implications in the metabolism of nitrate in both organisms.
在小鼠中，对分枝杆菌、沙门氏菌和利什曼原虫感染的天然抗性或易感性由一个名为Bcg的基因控制。Bcg调节巨噬细胞限制摄入寄生虫细胞内复制的能力，并被认为调节该细胞的一种关键杀菌机制。最近，我们克隆了Bcg基因，并表明它编码一种名为Nramp的新型巨噬细胞特异性膜蛋白。在公共数据库中对与Nramp同源的序列进行常规搜索时，鉴定出3个表达序列标签（EST），它们与哺乳动物蛋白有很强的相似性。我们报告了与哺乳动物Nramp的植物同源物（OsNramp1）相对应的全长cDNA克隆的鉴定和克隆。预测的植物蛋白氨基酸序列表明，它与其哺乳动物对应物有显著程度的相似性（60%同源性），包括跨膜结构域、糖基化信号和共有转运基序的数量、位置和组成相同，这表明这两种蛋白具有相同的整体二级结构和膜组织。这种高度的结构相似性表明这两种蛋白可能在功能上相关，可能通过共同的转运机制。RNA杂交研究和RT-PCR分析表明，OsNramp1 mRNA主要在根中表达，在叶/茎中仅以极低水平表达。DNA杂交研究表明，OsNramp1不是一个单一基因，而是一个新基因家族的一部分，该家族在所有测试的植物中都有几个成员，包括水稻、小麦和玉米等谷物，以及常见的杂草物种。讨论了巨噬细胞特异性哺乳动物Nramp与其OsNramp1植物同源物之间显著的保守程度及其对两种生物体中硝酸盐代谢可能的影响。
