Departments of Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, CA 94158, USA.
Proc Natl Acad Sci U S A. 2010 Mar 2;107(9):4170-5. doi: 10.1073/pnas.0914094107. Epub 2010 Feb 11.
Under mating conditions, yeast cells adopt a characteristic pear-shaped morphology, called a "shmoo," as they project a cell extension toward their mating partners. Mating partners make contact at their shmoo tips, dissolve the intervening cell wall, and fuse their plasma membranes. We identified mutations in ERG4, encoding the enzyme that catalyzes the last step of ergosterol biosynthesis, that impair both shmoo formation and cell fusion. Upon pheromone treatment, erg4Delta mutants polarized growth, lipids, and proteins involved in mating but did not form properly shaped shmoos and fused with low efficiency. Supplementation with ergosterol partially suppressed the shmooing defect but not the cell fusion defect. By contrast, removal of the Erg4 substrate ergosta-5,7,22,24(28)-tetraenol, which accumulates in erg4Delta mutant cells and contains an extra double bond in the aliphatic chain of the sterol, restored both shmooing and cell fusion to wild-type levels. Thus, a two-atom change in the aliphatic moiety of ergosterol is sufficient to obstruct cell shape remodeling and cell fusion.
在交配条件下，酵母细胞采用一种特征性的梨形形态，称为“shmoo”，因为它们向交配伙伴伸出一个细胞延伸。交配伙伴在 shmoo 尖端接触，溶解中间的细胞壁，并融合它们的质膜。我们鉴定出编码催化麦角固醇生物合成最后一步的酶的 ERG4 基因突变，该突变既损害了 shmoo 形成又损害了细胞融合。在交配信息素处理后，erg4Δ 突变体极化生长、与交配相关的脂质和蛋白质，但不能形成适当形状的 shmoos，融合效率低。添加麦角固醇部分抑制了 shmoo 缺陷，但不能抑制细胞融合缺陷。相比之下，去除 Erg4 底物麦角甾-5,7,22,24(28)-四烯醇，它在 erg4Δ 突变体细胞中积累，并且在固醇的脂链中含有一个额外的双键，将 shmoo 和细胞融合恢复到野生型水平。因此，麦角固醇脂族部分的两个原子变化足以阻碍细胞形状重塑和细胞融合。
