Department of Cellular and Molecular Physiology, Penn State College of Medicine, 500 University Drive, Hershey, PA 17033, USA.
Membranes (Basel). 2014 Sep 3;4(3):608-29. doi: 10.3390/membranes4030608.
When Saccharomyces cerevisiae is starved of glucose, the gluconeogenic enzymes fructose-1,6-bisphosphatase (FBPase), phosphoenolpyruvate carboxykinase, isocitrate lyase, and malate dehydrogenase, as well as the non-gluconeogenic enzymes glyceraldehyde-3-phosphate dehydrogenase and cyclophilin A, are secreted into the periplasm. In the extracellular fraction, these secreted proteins are associated with small vesicles that account for more than 90% of the total number of extracellular structures observed. When glucose is added to glucose-starved cells, FBPase is internalized and associated with clusters of small vesicles in the cytoplasm. Specifically, the internalization of FBPase results in the decline of FBPase and vesicles in the extracellular fraction and their appearance in the cytoplasm. The clearance of extracellular vesicles and vesicle-associated proteins from the extracellular fraction is dependent on the endocytosis gene END3. This internalization is regulated when cells are transferred from low to high glucose. It is rapidly occurring and is a high capacity process, as clusters of vesicles occupy 10%-20% of the total volume in the cytoplasm in glucose re-fed cells. FBPase internalization also requires the VPS34 gene encoding PI3K. Following internalization, FBPase is delivered to the vacuole for degradation, whereas proteins that are not degraded may be recycled.
当酿酒酵母耗尽葡萄糖时，糖异生酶果糖-1,6-二磷酸酶 (FBPase)、磷酸烯醇丙酮酸羧激酶、异柠檬酸裂合酶、苹果酸脱氢酶以及非糖异生酶甘油醛-3-磷酸脱氢酶和亲环蛋白 A 会被分泌到周质中。在细胞外部分，这些分泌蛋白与小泡相关联，这些小泡占观察到的总细胞外结构的 90%以上。当向葡萄糖饥饿的细胞中添加葡萄糖时，FBPase 被内化并与细胞质中的小泡簇相关联。具体来说，FBPase 的内化导致细胞外部分的 FBPase 和小泡减少，而在细胞质中出现。细胞外小泡和小泡相关蛋白从细胞外部分的清除依赖于内吞基因 END3。当细胞从低葡萄糖转移至高葡萄糖时，这种内化受到调节。它是快速发生的，并且是一个高容量的过程，因为在重新喂食葡萄糖的细胞中，小泡簇占据细胞质总容积的 10%-20%。FBPase 的内化还需要编码 PI3K 的 VPS34 基因。内化后，FBPase 被递送到液泡进行降解，而未降解的蛋白质可能被回收。
