Regulation of vacuolar acidity by PtdIns3P and PtdIns(35)P2 in Saccharomyces cerevisiae.

酵母菌是单细胞生物，内部有一个称为液泡的隔间，它可以吸收不需要的蛋白质（有点像胃）并储存食物。为了正常的功能，空泡内部必须是酸性的（就像胃一样），这是由一个叫做空泡ATP酶（V-ATP酶）的微小泵介导的。V-ATP酶位于液泡表面，将质子（酸性是由过量的质子引起的）泵入液泡内部，这一过程需要相当大的能量消耗。液泡被一层由脂质组成的膜包裹着，这层膜将液泡与细胞的其余部分隔开。我们特别感兴趣的是两种脂质，它们是一组称为聚磷酸肌醇（PPin）的一部分。这两种PPIn虽然只占液泡膜中脂质的很小一部分，但负责介导多种功能，并且是液泡变酸所需的。我们试图找出这些PPin是如何改变液泡内部的酸度的。特别感兴趣的是PPIns如何影响V-ATP酶泵。我们将做的实验类型的一个例子是从酵母中纯化液泡并向其中添加PPIn;然后我们可以测量V-ATPase泵在不同PPIn存在下的活性。通过这样的实验，我们应该建立PPIn形成和液泡酸度之间的机械联系。为什么研究很重要？首先，酵母是造成世界上相当大一部分食品供应的污染和腐败的原因。弱酸是常用的具有抗真菌作用的食品添加剂。除了这样的弱酸酵母细胞PPIn水平和细胞内pH值的变化。我们的工作将调查PPIn功能和液泡酸化，并允许更好地了解酵母的应激反应。最终，酵母应激反应的知识将导致更好的抗真菌食品添加剂的设计。此外，PPIn调节pH的机制可能与其他具有液泡的生物（如植物）共享。植物，像酵母一样，必须科普各种压力，因此我们的工作很可能对农业产生广泛的影响。

Yeasts are single celled organisms and contain an internal compartment called the vacuole, which digests unwanted proteins (a bit like the stomach) and stores food. For proper function the inside of the vacuole must be made acidic (again like the stomach), and this is mediated by a tiny pump called the vacuolar ATPase (V-ATPase). The V-ATPase is on the surface of the vacuole and pumps protons (acidity is caused by an excess of protons) into the vacuole interior in a process that requires considerable expenditure of energy. The vacuole is encapsulated by a membrane consisting of lipids, which separates it from the rest of the cell. We are particularly interested in two lipids, which are part of a group called polyphosphoinositides (PPIn). These two PPIn, although comprising only a very small fraction of the lipids in the vacuole membrane, are responsible for mediating a wide variety of functions and are required for the vacuole to be come acidic. We are trying to find out how these PPIn are able to change the acidity of the interior of the vacuole. Of particular interest will be how the PPIns might affect the V-ATPase pump. An example of the type of experiments that we will do is to purifiy vacuoles from yeast and add PPIn to them; we can then measure how active the V-ATPase pump is in the presence of different PPIn. By doing such experiments we should establish a mechanistic link between PPIn formation and vacuole acidity. Why is the research important? Firstly, yeasts are responsible for contamination and spoilage of a significant proportion of the World's food supply. Weak acids are frequently used food additives that have anti-fungal action. Addition of such weak acids to yeast causes changes in cellular PPIn levels and intracellular pH. Our work will investigate PPIn function and vacuolar acidification, and allow greater understanding of yeast stress responses. Ultimately, knowledge of yeast stress responses will lead to the design of better anti-fungal food additives. Additionally it is likely that the mechanisms of pH regulation by PPIn will be shared other organisms that have a vacuole such as plants. Plants, like yeasts, have to cope with a variety of stresses, so our work may well have wide implications for agriculture.