Uccelletti D, Pacelli V, Mancini P, Palleschi C
Fondation Institut Pasteur-Fondazione Cenci-Bolognetti, Department of Developmental and Cell Biology, University of Rome La Sapienza, Rome, Italy.
Yeast. 2000 Sep 15;16(12):1161-71. doi: 10.1002/1097-0061(20000915)16:12<1161::AID-YEA612>3.0.CO;2-W.
We studied the cell wall alterations that occur in mutants of Kluyveromyces lactis impaired in glycosylation. The mutants belong to four complementation groups named vga1 to vga4 (vanadate glycosylation affected), characterized by sodium orthovanadate resistance and alteration of the glycosylation profile of native invertase. A drastic reduction of the alkali-soluble fraction of the beta-D-glucan was observed in vga1, vga2 and vga3 cells, accompanied by an increase in the chitin content of the cell wall. In vga4 cells, both beta-D-glucan fractions (alkali-soluble and alkali-insoluble) were reduced to about half of the corresponding wild-type value but the chitin content was normal. A protein related to Fks1p, the catalytic subunit of the major 1,3-beta-D-glucan synthase of S. cerevisiae, was detected in K. lactis. The amount of this Fks1p-like protein increased 7-10 times in vga1, vga2 and vga3 mutants as compared to wild-type cells; the same strains released significant amounts of beta-D-glucan in the culture supernatant. These mutations also resulted in abnormally thick cell walls with conspicuous irregularities in the structure, as revealed by electron microscopy and by an altered resistance to Zymolyase. The observed high responsiveness of cell wall phenotypes to alterations of glycosylation make K. lactis an attractive system for studying the interconnections between these processes.
我们研究了在糖基化方面存在缺陷的乳酸克鲁维酵母突变体中发生的细胞壁改变。这些突变体属于四个互补群，命名为vga1至vga4（钒酸盐糖基化受影响），其特征是对原钒酸钠具有抗性且天然转化酶的糖基化谱发生改变。在vga1、vga2和vga3细胞中，观察到β-D-葡聚糖的碱溶性部分急剧减少，同时细胞壁中几丁质含量增加。在vga4细胞中，β-D-葡聚糖的两个部分（碱溶性和碱不溶性）均降至相应野生型值的约一半，但几丁质含量正常。在乳酸克鲁维酵母中检测到一种与酿酒酵母主要1,3-β-D-葡聚糖合酶的催化亚基Fks1p相关的蛋白质。与野生型细胞相比，vga1、vga2和vga3突变体中这种Fks1p样蛋白的量增加了7至10倍；相同菌株在培养上清液中释放出大量的β-D-葡聚糖。这些突变还导致细胞壁异常增厚，结构明显不规则，这通过电子显微镜和对溶菌酶的抗性改变得以揭示。观察到的细胞壁表型对糖基化改变的高反应性使乳酸克鲁维酵母成为研究这些过程之间相互联系的有吸引力的系统。
