Iwaki Tomoko, Iefuji Haruyuki, Hiraga Yoshikazu, Hosomi Akira, Morita Tomotake, Giga-Hama Yuko, Takegawa Kaoru
Research Center, Asahi Glass Co. Ltd, Yokohama, Kanagawa 221-8755, Japan.
Department of Life Sciences, Faculty of Agriculture, Kagawa University, Miki-cho, Kagawa 761-0795, Japan.
Microbiology (Reading). 2008 Mar;154(Pt 3):830-841. doi: 10.1099/mic.0.2007/011155-0.
Sterols are a major class of membrane lipids in eukaryotes. In Schizosaccharomyces pombe, sterol 24-C-methyltransferase (Erg6p), C-8 sterol isomerase (Erg2p), C-5 sterol desaturase (Erg31p, Erg32p), C-22 sterol desaturase (Erg5p) and C-24 (28) sterol reductase (Sts1p/Erg4p) have been predicted, but not yet determined, to catalyse a sequence of reactions from zymosterol to ergosterol. Disruption mutants of these genes were unable to synthesize ergosterol, and most were tolerant to the polyene drugs amphotericin B and nystatin. Disruption of erg31(+) or erg32(+) did not cause ergosterol deficiency or tolerance to polyene drugs, indicating that the two C-5 sterol desaturases have overlapping functions. GFP-tagged DRM (detergent-resistant membrane)-associated protein Pma1p localized to the plasma membrane in ergDelta mutants. DRM fractionation revealed that the association between Pma1-GFP and DRM was weakened in erg6Delta but not in other erg mutants. Several GFP-tagged plasma membrane proteins were tested, and an amino acid permease homologue, SPBC359.03c, was found to mislocalize to intracellular punctate structures in the ergDelta mutants. These results indicate that these proteins are responsible for ergosterol biosynthesis in fission yeast, similar to the situation in Saccharomyces cerevisiae. Furthermore, in fission yeast, ergosterol is important for plasma membrane structure and function and for localization of plasma membrane proteins.
甾醇是真核生物中一类主要的膜脂。在粟酒裂殖酵母中，甾醇24 - C - 甲基转移酶（Erg6p）、C - 8甾醇异构酶（Erg2p）、C - 5甾醇去饱和酶（Erg31p、Erg32p）、C - 22甾醇去饱和酶（Erg5p）和C - 24（28）甾醇还原酶（Sts1p/Erg4p）已被预测，但尚未确定，它们催化从酵母甾醇到麦角甾醇的一系列反应。这些基因的破坏突变体无法合成麦角甾醇，并且大多数对多烯药物两性霉素B和制霉菌素具有耐受性。erg31(+)或erg32(+)的破坏不会导致麦角甾醇缺乏或对多烯药物的耐受性，这表明这两种C - 5甾醇去饱和酶具有重叠功能。绿色荧光蛋白（GFP）标记的耐去污剂膜（DRM）相关蛋白Pma1p定位于ergDelta突变体的质膜。DRM分级分离显示，在erg6Delta中，Pma1 - GFP与DRM之间的关联减弱，但在其他erg突变体中未减弱。测试了几种GFP标记的质膜蛋白，发现一种氨基酸通透酶同源物SPBC359.03c在ergDelta突变体中错误定位于细胞内点状结构。这些结果表明，这些蛋白质与酿酒酵母中的情况类似，负责裂殖酵母中的麦角甾醇生物合成。此外，在裂殖酵母中，麦角甾醇对于质膜结构和功能以及质膜蛋白的定位很重要。
