The rice mutant esp2 greatly accumulates the glutelin precursor and deletes the protein disulfide isomerase
The rice mutant esp2 greatly accumulates the glutelin precursor and deletes the protein disulfide isomerase
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DOI：
10.1104/pp.010624
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发表时间：
2002-04-01
期刊：
影响因子：
7.4
通讯作者：
Kumamaru, T
中科院分区：
文献类型：
--
作者：
Takemoto, Y;Coughlan, SJ;Kumamaru, T
水稻（Oryza sativa）积累醇溶蛋白和谷蛋白作为贮藏蛋白。后一种贮藏蛋白在内质网（ER）上合成为57 kD的前谷蛋白，然后在蛋白质贮藏泡中加工成酸性和碱性亚基。三个esp 2突变体CM 1787、EM 44和EM 747含有比正常更大量的57-kD多肽和相应更低水平的酸性和碱性谷蛋白亚基。电子显微镜观察显示，esp 2含有正常外观的含谷蛋白的蛋白体（PB-II），但缺乏正常的含醇溶谷蛋白的PB（PB-I）。相反，许多小的ER衍生的PB的均匀大小（0.5 μ m的直径）和低电子密度很容易观察到。纯化的亚细胞组分和免疫细胞化学在电子显微镜水平的免疫印迹分析表明，这些新的PB含有57-kD的前谷蛋白前体和醇溶谷蛋白多肽。57-kD的谷蛋白原提取与1%（v/v）的乳酸溶液后，仅去除富含半胱氨酸的醇溶谷蛋白多肽，这表明这些蛋白质形成谷蛋白-醇溶谷蛋白聚集体通过ER内腔内的链间二硫键。esp 2突变体的胚乳含有内腔分子伴侣、结合蛋白和钙连接蛋白，但在蛋白质和RNA水平上缺乏蛋白质二硫键异构酶（PDI）。PDI的转录本仅在野生型种子发育的早期阶段在种子中表达。这些结果表明，PDI起着至关重要的作用，在ER腔内的谷蛋白和醇溶谷蛋白多肽的隔离。
Rice (Oryza sativa) accumulates prolamins and glutelins as storage proteins. The latter storage protein is synthesized on the endoplasmic reticulum (ER) as a 57-kD proglutelin precursor, which is then processed into acidic and basic subunits in the protein storage vacuole. Three esp2 mutants CM1787, EM44, and EM747, contain larger amounts of the 57-kD polypeptide and corresponding lower levels of acidic and basic glutelin subunits than normal. Electron microscopic observation revealed that esp2 contained normal-appearing glutelin-containing protein bodies (PB-II), but lacked the normal prolamin-containing PB (PB-I). Instead, numerous small ER-derived PBs of uniform size (0.5 mum in diameter) and low electron density were readily observed. Immunoblot analysis of purified subcellular fractions and immunocytochemistry at the electron microscopy level showed that these new PBs contained the 57-kD proglutelin precursor and prolamin polypeptides. The 57-kD proglutelin was extracted with 1% (v/v) lactic acid solution only after removal of cysteine-rich prolamin polypeptides, suggesting that these proteins form glutelin-prolamin aggregates via interchain disulfide bonds within the ER lumen. The endosperm of esp2 mutants contains the lumenal chaperones, binding protein and calnexin, but lacks protein disulfide isomerase (PDI) at the protein and RNA levels. The transcript of PDI was expressed in the seed only during the early stage of seed development in the wild type. These results suggest that PDI plays an essential role in the segregation of proglutelin and prolamin polypeptides within the ER lumen.