Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, China.
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo 113-8657, Japan.
J Biochem. 2018 Apr 1;163(4):293-304. doi: 10.1093/jb/mvx082.
OSW2 is a meiotically-induced gene required for spore wall formation. osw2Δ spores are sensitive to ether treatment. Except for this phenotype, the mutants do not show obvious sporulation defects; thus, its function remains elusive. We found that deletion of both OSW2 and CHS3 results in a synthetic sporulation defect. The spore wall is composed of four layers, and chs3Δ spores lack the outer two (chitosan and dityrosine) layers. Thus, Osw2 is involved in the assembly of the inner (glucan and mannan) layers. In agreement with this notion, a glycosylphosphatidylinositol-anchored protein reporter mislocalizes in osw2Δ spores. The osw2Δ mutation also exhibited a severe synthetic sporulation defect when combined with the deletion of a ß-1,6-glucan synthesis-related gene, BIG1. Osw2 is localized to the prospore membrane during sporulation. However, it disappears in mature spores, indicating that it is not a structural component of the spore wall. Given that Osw2 contains a probable 2-dehydropantoate 2-reductase domain, it may mediate an enzymatic reaction. Osw2 shows a weak similarity to other 2-dehydropantoate 2-reductase domain-containing proteins, Svl3 and Pam1. A pam1Δsvl3Δ mutant exhibits vegetative cell and spore wall defects. Thus, the 2-dehydropantoate 2-reductase domain-containing proteins may have a similar function in glucan and/or mannan layer assembly.
OSW2 是一个减数分裂诱导的基因，对于孢子壁的形成是必需的。osw2Δ 孢子对乙醚处理敏感。除了这个表型外，突变体没有明显的孢子形成缺陷；因此，其功能仍然难以捉摸。我们发现，OSW2 和 CHS3 的缺失都导致了孢子形成的合成缺陷。孢子壁由四层组成，chs3Δ 孢子缺乏外层的两层（几丁质和二酪氨酸）。因此，Osw2 参与了内层（葡聚糖和甘露聚糖）层的组装。这一观点与 Osw2 缺失导致糖基磷脂酰肌醇锚定蛋白报告基因错误定位在 osw2Δ 孢子中的结果一致。osw2Δ 突变与 β-1,6-葡聚糖合成相关基因 BIG1 的缺失结合时，也表现出严重的合成孢子形成缺陷。Osw2 在孢子形成过程中定位于前孢子膜。然而，在成熟的孢子中它消失了，表明它不是孢子壁的结构成分。鉴于 Osw2 包含一个可能的 2-脱水葡萄糖酸 2-还原酶结构域，它可能介导一个酶反应。Osw2 与其他含有 2-脱水葡萄糖酸 2-还原酶结构域的蛋白质，Svl3 和 Pam1，显示出较弱的相似性。一个 pam1Δsvl3Δ 突变体表现出营养细胞和孢子壁缺陷。因此，2-脱水葡萄糖酸 2-还原酶结构域蛋白可能在葡聚糖和/或甘露聚糖层组装中具有相似的功能。
