CBAA, Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Lisbon, Portugal.
PLoS One. 2013 Jul 2;8(7):e68165. doi: 10.1371/journal.pone.0068165. Print 2013.
Zygosaccharomyces rouxii is a fructophilic yeast than can grow at very high sugar concentrations. We have identified an ORF encoding a putative fructose/H(+) symporter in the Z. rouxii CBS 732 genome database. Heterologous expression of this ORF in a S. cerevisiae strain lacking its own hexose transporters (hxt-null) and subsequent kinetic characterization of its sugar transport activity showed it is a high-affinity low-capacity fructose/H(+) symporter, with Km 0.45 ± 0.07 mM and Vmax 0.57 ± 0.02 mmol h(-1) (gdw)(-1). We named it ZrFsy1. This protein also weakly transports xylitol and sorbose, but not glucose or other hexoses. The expression of ZrFSY1 in Z. rouxii is higher when the cells are cultivated at extremely low fructose concentrations (<0.2%) and on non-fermentable carbon sources such as mannitol and xylitol, where the cells have a prolonged lag phase, longer duplication times and change their microscopic morphology. A clear phenotype was determined for the first time for the deletion of a fructose/H(+) symporter in the genome where it occurs naturally. The effect of the deletion of ZrFSY1 in Z. rouxii cells is only evident when the cells are cultivated at very low fructose concentrations, when the ZrFsy1 fructose symporter is the main active fructose transporter system.
鲁氏接合酵母是一种嗜果糖酵母，能够在非常高的糖浓度下生长。我们在鲁氏接合酵母 CBS 732 基因组数据库中鉴定出一个编码假定果糖/H(+)同向转运蛋白的 ORF。在缺乏自身己糖转运蛋白（hxt-null）的酿酒酵母菌株中异源表达该 ORF，并对其糖转运活性进行动力学表征，结果表明它是一种高亲和力低容量的果糖/H(+)同向转运蛋白，Km 为 0.45 ± 0.07 mM，Vmax 为 0.57 ± 0.02 mmol h(-1) (gdw)(-1)。我们将其命名为 ZrFsy1。该蛋白还较弱地转运木糖醇和山梨醇，但不转运葡萄糖或其他己糖。当细胞在极低的果糖浓度（<0.2%）和非发酵性碳源（如甘露醇和木糖醇）下培养时，ZrFSY1 在鲁氏接合酵母中的表达更高，此时细胞具有延长的迟滞期、更长的复制时间并改变其微观形态。这是首次在天然存在果糖/H(+)同向转运蛋白的基因组中删除该蛋白，确定了一个明确的表型。只有在细胞在非常低的果糖浓度下培养时，ZrFSY1 的缺失才会对鲁氏接合酵母细胞产生影响，此时 ZrFsy1 果糖转运蛋白是主要的活性果糖转运系统。
