Shimada Tomoo, Fuji Kentaro, Tamura Kentaro, Kondo Maki, Nishimura Mikio, Hara-Nishimura Ikuko
Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Proc Natl Acad Sci U S A. 2003 Dec 23;100(26):16095-100. doi: 10.1073/pnas.2530568100. Epub 2003 Dec 4.
The seeds of higher plants accumulate large quantities of storage protein. During seed maturation, storage protein precursors synthesized on rough endoplasmic reticulum are sorted to protein storage vacuoles, where they are converted into the mature forms and accumulated. Previous attempts to determine the sorting machinery for storage proteins have not been successful. Here we show that a type I membrane protein, AtVSR1/AtELP, of Arabidopsis functions as a sorting receptor for storage proteins. The atvsr1 mutant missorts storage proteins by secreting them from cells, resulting in an enlarged and electron-dense extracellular space in the seeds. The atvsr1 seeds have distorted cells and smaller protein storage vacuoles than do WT seeds, and atvsr1 seeds abnormally accumulate the precursors of two major storage proteins, 12S globulin and 2S albumin, together with the mature forms of these proteins. AtVSR1 was found to bind to the C-terminal peptide of 12S globulin in a Ca2+-dependent manner. These findings demonstrate a receptor-mediated transport of seed storage proteins to protein storage vacuoles in higher plants.
高等植物的种子积累了大量的贮藏蛋白。在种子成熟过程中，在内质网上合成的贮藏蛋白前体被分选到蛋白贮藏液泡中，在那里它们被转化为成熟形式并积累起来。以往确定贮藏蛋白分选机制的尝试均未成功。在此，我们表明拟南芥的一种I型膜蛋白AtVSR1/AtELP作为贮藏蛋白的分选受体发挥作用。atvsr1突变体通过将贮藏蛋白分泌到细胞外而导致分选错误，从而使种子中的细胞外空间增大且电子密度增加。与野生型种子相比，atvsr1种子的细胞变形，蛋白贮藏液泡更小，并且atvsr1种子异常积累了两种主要贮藏蛋白12S球蛋白和2S清蛋白的前体以及这些蛋白的成熟形式。研究发现AtVSR1以Ca2+依赖的方式与12S球蛋白的C末端肽结合。这些发现证明了高等植物中种子贮藏蛋白通过受体介导运输到蛋白贮藏液泡中。
