Analysis of the role of the ubiquitin system in the regulation of yeast carbohydrate metabolism

每一种生物，无论是人类还是单个细胞，都有能力在丰年和饥荒之间调整自己的新陈代谢。丰富的营养物质使能量储备得以储存，并在时间贫乏时释放出来。细胞和生物体通过快速和可逆的关键酶的激活来改变其代谢途径的操作，从而有效地响应营养丰富，这些酶在响应营养信号时被打开或关闭。哺乳动物中有一种这样的酶被称为AMP依赖性蛋白激酶（AMPK），它对细胞ATP/AMP水平作出反应，关闭或打开能量消耗代谢途径以保持恒定的能量水平。我们的研究集中在进化相关的酵母AMPK酶，SNF1激酶，它对葡萄糖水平有类似的反应，葡萄糖是它最喜欢的能量来源。这个简单的酵母系统将用于探索该酶家族的分子调控。我们发现SNF1激酶上附着一种叫做泛素（Ub）的小蛋白，这可能会影响它的稳定性、细胞位置和活性，所有这些过程都很容易有助于调节这种酶。SNF1激酶的磷酸化和核定位是其活性所必需的，但控制这些事件的分子机制尚不清楚。为了阐明导致Ub附着于SNF1激酶的酶和潜在触发因素，以及当葡萄糖供应改变时这种附着的结果，我们将研究SNF1激酶蛋白水平的变化，使用荧光蛋白标签和显微镜的核定位，以及当我们阻断SNF1激酶泛素化时对不同糖源的代谢适应。阐明Ub在SNF1激酶功能中的作用可能有助于了解人类代谢是如何被调节的。代谢效率低下会导致代谢综合征，包括糖尿病、肥胖和加速心脏病。在加拿大，这种情况越来越普遍，影响到越来越多的年轻人。两种增强AMPK活性的药物（运动和二甲双胍）可以提高代谢效率，这表明我们的发现有可能极大地有益于人类的代谢。

Every organism, whether a human or a single cell, has the ability to adapt its metabolism between times of feast and famine. Abundant nutrients enable energy stores to be laid down and later released when times are lean. Cells and organisms efficiently respond to nutrient abundance by altering the operation of their metabolic pathways through the rapid and reversible activation of key enzymes that are turned on or off in response to nutrient signals. One such enzyme in mammals is called AMP-dependent protein kinase (AMPK), that responds to cellular ATP/AMP levels, turning energy consuming metabolic pathways off or on to preserve a constant energy level. Our studies focus on the evolutionarily related yeast AMPK enzyme, SNF1 kinase, which responds similarly to glucose levels, its favorite energy source. This simple yeast system will be used to explore the molecular regulation of this enzyme family. We find that SNF1 kinase has a small protein called ubiquitin (Ub) attached to it, which may affect its stability, cellular location, and activity, all processes that could readily contribute to regulation of this enzyme. Phosphorylation of SNF1 kinase and nuclear localization are required for activity, but the molecular mechanisms controlling these events remain unknown. To shed light on the enzymes and potential triggers that cause attachment of Ub to SNF1 kinase, and the result of that attachment when the glucose supplies change, we will examine changes to SNF1 kinase protein levels, nuclear localization using fluorescent protein tags and microscopy, and metabolic adaptation to different sugar sources when we block SNF1 kinase ubiquitination. Elucidating the role of Ub in SNF1 kinase function may provide insight into how human metabolism is regulated. Inefficient metabolism contributes to metabolic syndrome, encompassing diabetes, obesity, and accelerated heart disease. This is rising in prevalence and affecting increasingly younger people in Canada. Two agents that enhance AMPK activity (exercise and Metformin) improve metabolic efficiency, suggesting that our findings have the potential to greatly benefit human metabolism.