Popolo L, Gilardelli D, Bonfante P, Vai M
Sezione di Biochimica Comparata, Dipartimento di Fisiologia e Biochimica Generali, Universitá degli Studi di Milano, Italy.
J Bacteriol. 1997 Jan;179(2):463-9. doi: 10.1128/jb.179.2.463-469.1997.
The GGP1/GAS1 gene codes for a glycosylphosphatidylinositol-anchored plasma membrane glycoprotein of Saccharomyces cerevisiae. The ggp1delta mutant shows morphogenetic defects which suggest changes in the cell wall matrix. In this work, we have investigated cell wall glucan levels and the increase of chitin in ggp1delta mutant cells. In these cells, the level of alkali-insoluble 1,6-beta-D-glucan was found to be 50% of that of wild-type cells and was responsible for the observed decrease in the total alkali-insoluble glucan. Moreover, the ratio of alkali-soluble to alkali-insoluble glucan almost doubled, suggesting a change in glucan solubility. The increase of chitin in ggp1delta cells was found to be essential since the chs3delta ggp1delta mutations determined a severe reduction in the growth rate and in cell viability. Electron microscopy analysis showed the loss of the typical structure of yeast cell walls. Furthermore, in the chs3delta ggp1delta cells, the level of alkali-insoluble glucan was 57% of that of wild-type cells and the alkali-soluble/alkali-insoluble glucan ratio was doubled. We tested the effect of inhibition of chitin synthesis also by a different approach. The ggp1delta cells were treated with nikkomycin Z, a well-known inhibitor of chitin synthesis, and showed a hypersensitivity to this drug. In addition, studies of genetic interactions with genes related to the construction of the cell wall indicate a synthetic lethal effect of the ggp1delta kre6delta and the ggp1delta pkc1delta combined mutations. Our data point to an involvement of the GGP1 gene product in the cross-links between cell wall glucans (1,3-beta-D-glucans with 1,6-beta-D-glucans and with chitin). Chitin is essential to compensate for the defects due to the lack of Ggp1p. Moreover, the activities of Ggp1p and Chs3p are essential to the formation of the organized structure of the cell wall in vegetative cells.
GGP1/GAS1基因编码酿酒酵母的一种糖基磷脂酰肌醇锚定的质膜糖蛋白。ggp1δ突变体表现出形态发生缺陷，这表明细胞壁基质发生了变化。在这项研究中，我们研究了ggp1δ突变体细胞中细胞壁葡聚糖水平和几丁质的增加情况。在这些细胞中，发现碱不溶性1,6-β-D-葡聚糖的水平是野生型细胞的50%，并且这是观察到的总碱不溶性葡聚糖减少的原因。此外，碱溶性与碱不溶性葡聚糖的比例几乎增加了一倍，表明葡聚糖溶解性发生了变化。发现ggp1δ细胞中几丁质的增加是必不可少的，因为chs3δ ggp1δ突变导致生长速率和细胞活力严重降低。电子显微镜分析显示酵母细胞壁典型结构的丧失。此外，在chs3δ ggp1δ细胞中，碱不溶性葡聚糖的水平是野生型细胞的57%，碱溶性/碱不溶性葡聚糖比例增加了一倍。我们还通过另一种方法测试了抑制几丁质合成的效果。用几丁质合成的著名抑制剂尼可霉素Z处理ggp1δ细胞，发现其对该药物过敏。此外，与细胞壁构建相关基因的遗传相互作用研究表明，ggp1δ kre6δ和ggp1δ pkc1δ联合突变具有合成致死效应。我们的数据表明GGP1基因产物参与了细胞壁葡聚糖（1,3-β-D-葡聚糖与1,6-β-D-葡聚糖以及与几丁质）之间的交联。几丁质对于弥补由于缺乏Ggp1p导致的缺陷至关重要。此外，Ggp1p和Chs3p的活性对于营养细胞中细胞壁有组织结构的形成至关重要。
