Role of GPI anchor in plant cell wall construction

在缺磷条件下诱导合成的寡根Spirodela oligorrhiza紫色酸性磷酸酶（PAP）首次被证实是高等植物中发现的糖基磷脂酰肌醇（GPI）锚定蛋白。为了了解gpi锚定PAP的初级结构，我们通过cDNA文库筛选和从缺磷植物（-P植物）中快速扩增cDNA，获得了其cDNA克隆。寡根菌PAP cDNA开放阅读框全长1365 bp，编码455个氨基酸的蛋白。其氨基酸序列与拟南芥（Arabidopsis thaliana）和菜豆（Phaseolus vulgaris）的PAP序列相似性分别为82%和80%。氨基酸残基Ala-439和两个较小的氨基酸残基Asp和Ser被预测为gpi锚定ω-位点。在推定ω-位点上游缺少双基序表明PAP是一种细胞壁蛋白。这一假设得到了发现的支持，即PAP是通过纤维素酶消化细胞壁部分释放的。推测GPI锚点是将PAP运送到细胞壁的信号。利用- p植物根系的免疫组织化学结果表明，PAP优先分布在根最外层的皮质细胞中，而不是在表皮中，这表明它在缺磷条件下获取无机磷酸盐的作用。利用多形地藓培养细胞筛选了新的gpi锚定蛋白。放射性标记的乙醇胺和神秘酸都被显著地结合到一个47 kDa的蛋白中，该蛋白是苔藓唯一的主要分泌蛋白。该蛋白的n端氨基酸测序结果表明，该蛋白为47 kDa蛋白，与金车前草（cratererostigma plantagineum）中的干燥相关蛋白相似。苔藓蛋白将是一种新的gpi锚定蛋白。

The Spirodela oligorrhiza purple acid phosphatase (PAP) inducibly synthesized under phosphate-deficient conditions was at the first time proved to be a glycosylphosphatidylinositol (GPI)-anchored protein found in higher plants. To know the primary structure of the GPI-anchored PAP its cDNA clone has been obtained by a combination of cDNA library screening and 5' rapid amplification of cDNA from plants (-P plants) grown under phosphate-deficient conditions. The open reading frame of the S.oligorrhiza PAP cDNA consists of 1365 bp encoding a 455-amino acid protein. Its deduced amino acid sequence shows 82% and 80% similarity with that of PAP from Arabidopsis thaliana and Phaseolus vulgaris, respectively. The amino acid residue Ala-439 followed by two more small amino acid residues, Asp and Ser, is predicted to be the GPI-anchoring ω-site. The absence of a dibasic motif upstream of the putativeω-site suggests that the PAP is a cell wall protein. This presumption is supported by the finding that PAP was released by digestion of the cell wall fraction with cellulase. The GPI anchor is speculated to be a signal for transporting PAP to the cell wall. Immuno-histochemical results using-P plant roots demonstrate that PAP is preferentially distributed in the outer-most cortical cells of roots but not in the epidermis, suggesting its role for acquiring inorganic phosphate under phosphate-deficient conditions.Screening of new GPI-anchored proteins has beencarried out using cultured cells of the moss Marchantia polymorpha. Radio-labeled ethanolamine and mystic acid were both incorporated significantly into a 47 kDa protein which was the sole major secretory protein of the moss. The N-terminal amino acid sequencing of the protein indicates thatthe 47 kDa protein is a protein similar to the desiccation-related protein from Craterostigma plantagineum. The moss protein would be a new GPI-anchored protein.