Carlsberg Laboratory, DK-2500 Valby, Denmark.
J Cell Biochem. 2010 Jul 1;110(4):920-5. doi: 10.1002/jcb.22605.
Gene expression in micro-organisms is regulated according to extracellular conditions and nutrient concentrations. In Saccharomyces cerevisiae, non-transporting sensors with high sequence similarity to transporters, that is, transporter-like sensors, have been identified for sugars as well as for amino acids. An alternating-access model of the function of transporter-like sensors has been previously suggested based on amino acid sensing, where intracellular ligand inhibits binding of extracellular ligand. Here we studied the effect of intracellular glucose on sensing of extracellular glucose through the transporter-like sensor Snf3 in yeast. Sensing through Snf3 was determined by measuring degradation of Mth1 protein. High intracellular glucose concentrations were achieved by using yeast strains lacking monohexose transporters which were grown on maltose. The apparent affinity of extracellular glucose to Snf3 was measured for cells grown in non-fermentative medium or on maltose. The apparent affinity for glucose was lowest when the intracellular glucose concentration was high. The results conform to an alternating-access model for transporter-like sensors.
微生物中的基因表达是根据细胞外条件和营养浓度来调节的。在酿酒酵母中，已经鉴定出了与转运体具有高度序列相似性的非转运传感器，即转运体样传感器，这些传感器可用于检测糖和氨基酸。先前基于氨基酸感应提出了转运体样传感器功能的交替访问模型，其中细胞内配体抑制细胞外配体的结合。在这里，我们通过研究酵母中通过转运体样传感器 Snf3 感应细胞外葡萄糖的过程来研究细胞内葡萄糖的影响。通过测量 Mth1 蛋白的降解来确定通过 Snf3 的感应。通过使用缺乏单糖转运体的酵母菌株在麦芽糖上生长来实现高细胞内葡萄糖浓度。在非发酵培养基或麦芽糖上生长的细胞中测量了细胞外葡萄糖对 Snf3 的表观亲和力。当细胞内葡萄糖浓度高时，葡萄糖对 Snf3 的表观亲和力最低。结果符合转运体样传感器的交替访问模型。
