GLUCOSE SENSING AND SIGNALLING IN YEAST

葡萄糖是几乎所有细胞的主要碳和能量来源，因此它们感知葡萄糖并对其做出适当反应至关重要。这一点在哺乳动物中尤为重要，如果哺乳动物在葡萄糖感知方面存在微小缺陷，就会表现出严重的多效性表型，称为糖尿病。葡萄糖传感和信号传导对酵母具有特殊意义，因为它在很大程度上决定了生物体的新型发酵生活方式。我们的长期目标是了解酵母细胞如何感知葡萄糖并产生细胞内信号，以及这些信号如何被转导到影响细胞功能的靶蛋白。葡萄糖对酵母细胞的主要影响是基因表达的改变。葡萄糖抑制对葡萄糖生长的细胞不重要的基因的表达，并激活在葡萄糖上生长的细胞中需要的基因的表达。两个葡萄糖信号转导通路负责这些影响最近成为焦点。葡萄糖阻遏途径包括负责葡萄糖激活Mig 1阻遏物的蛋白激酶（Snf 1-Snf 4）和蛋白磷酸酶（Reg 1-Glc 7）。葡萄糖诱导途径包括膜中的两个葡萄糖传感器（Snf 3和Rgt 2），其结合葡萄糖并产生影响泛素连接酶蛋白复合物（SCFGrr 1）抑制Rgt 1阻遏物功能的能力的细胞内信号。为了理解葡萄糖诱导的机制（目标1），我们需要了解a）葡萄糖如何调节Rgt 1功能，B）SCFGrr 1蛋白复合物是否以及如何响应葡萄糖，c）葡萄糖传感器如何产生细胞内信号，以及d）作用于HXT 1的额外的新型葡萄糖信号转导途径的性质。为了理解葡萄糖阻遏（Aim 2）的机制，我们需要知道a）Mig 1是如何受葡萄糖调节的，B）Reg 1-Glc 7蛋白磷酸酶在调节Mig 1功能中的作用，以及c）Mig 2阻遏物的葡萄糖调节的新的、Snf 1非依赖性机制的性质。我们还将利用葡萄糖传感器和葡萄糖转运蛋白之间的结构和功能差异，以了解葡萄糖跨膜转运的机制（目标3）。

Glucose is the primary carbon and energy source for nearly all cells, so it is critical that they sense glucose and respond to it appropriately. The importance of this is especially apparent in mammals, which exhibit the severe pleiotropic phenotype called diabetes if they have even minor defects in glucose sensing. Glucose sensing and signaling is of special significance to yeast, because it largely determines the novel fermentative lifestyle of the organism. Our long-term goals are to understand how yeast cells sense glucose and generate intracellular signals, and how those signals are transduced to target proteins that affect cellular function. A major effect glucose has on yeast cells is alteration of gene expression. Glucose represses expression of genes not important to glucose-grown cells, and activates expression of genes in demand in cells growing on glucose. Two glucose signal transduction pathways responsible for these effects have recently come into focus. The glucose repression pathway includes a protein kinase (Snf1-Snf4) and a protein phosphatase (Reg1- Glc7) responsible for glucose activation of the Mig1 repressor. The glucose-induction pathway includes two glucose sensors in the membrane (Snf3 & Rgt2) that bind glucose and generate an intracellular signal that affects the ability of a ubiquitin ligase protein complex (SCFGrr1) to inhibit function of the Rgt1 repressor. To understand the mechanism of glucose induction (Aim 1), we need to learn a) how Rgt1 function is regulated by glucose, b) if and how the SCFGrr1 protein complex responds to glucose, c) how the glucose sensors generate an intracellular signal, and d) the nature of an additional, novel glucose signal transduction pathway that acts on HXT1. To understand the mechanism of glucose repression (Aim2), we need to know a) how Mig1 is regulated by glucose, b) the role of the Reg1-Glc7 protein phosphatase in regulating Mig1 function, and c) the nature of the novel, Snf1-independent mechanism for glucose regulation of the Mig2 repressor. We will also take advantage of structural and functional differences between the glucose sensors and glucose transporters to inform the mechanism of glucose transport across the membrane (Aim 3).