Structural and Fragment approaches to the modulation of O-GlcNAc in cells

许多控制细胞生物过程的大分子的功能可以通过一种叫做O-GlcNAc的糖的化学修饰而改变。有两种酶控制着这种化学修饰：一种是将糖添加到蛋白质中的转移酶（OGT），另一种是将糖去除的水解酶（OGA）。这种糖的添加类似于细胞中的其他控制机制，例如磷酸化，其中添加磷酸盐（与激酶一起）或去除磷酸盐（与磷酸酶一起）。关于磷酸化是如何发生的，以及它对细胞的影响，我们已经知道了很多——事实上，最近发现的许多药物都是对癌症等疾病有影响的激酶抑制剂。然而，O-GlcNAc修饰直到最近才被发现，我们现在才开始发现当修饰模式改变时细胞会发生什么。最近的一项发现是，O-GlcNAc修饰在维持健康的神经元中起作用，并且破坏对神经退行性疾病（如阿尔茨海默病）有一定影响。我们研究的目的是更多地了解这些酶，OGA和OGT，是什么样子的，以及它们是如何工作的。这些知识本身就很有趣，但它也提供了可用于设计可以与酶结合并改变其活性的小分子化合物的信息-有趣的是，我们可以增加或减少酶的工作速度。通过反复试验很难找到这么小的分子。最近发展起来的一种新技术是基于碎片的发现方法。这种方法不需要找到适合结合位点的完整分子，而是从识别结合的小分子片段开始。如果能够理解这些小片段结合的方式，那么化学家就可以设计改变，将这些片段合并或生长成具有正确性质的更大的化合物。我们将使用这些方法来发现改变OGA和OGT活性的小分子。然后将它们添加到细胞中，观察改变O-GlcNAc对细胞行为的影响。主要目的是了解对细胞生物学的影响，尽管这些化合物可能为药物设计提供一个起点。

The function of many of the large macromolecules that control biological processes in a cell can be changed by chemical modification with a sugar called O-GlcNAc. Two enzymes control this chemical modification: a transferase (OGT) that adds the sugar to the protein and a hydrolase (OGA) which removes it. This addition of a sugar is analogous to other mechanisms of control in the cell - such as phosphorylation where a phosphate is added (with a kinase) or removed (with a phosphatase). A great deal is known about how phosphorylation occurs and its consequences on the cell - indeed, many of the more recent drugs that have been discovered are kinase inhibitors that have an impact in conditions such as cancer. However, the O-GlcNAc modification has only recently been discovered and we are only now beginning to discover what happens to cells when the pattern of modification is changed. One recent discovery is that the O-GlcNAc modification has a role in maintaining healthy neurones, and disruption has some impact on neurodegenerative diseases such as Alzheimer's. The aim of our research is to understand more about what these enzymes, OGA and OGT, look like and how they work. This knowledge will be of interest in its own right, but it also provides information which can be used to design small molecule compounds that can bind to the enzymes and change their activity - interestingly, we can both increase and decrease how quickly the enzymes work. It is difficult to find such small molecules by trial and error. One new technique that has been developed recently is the method of fragment-based discovery. Instead of having to find the complete molecule that fits the binding site, this approach begins by identifying smaller pieces of molecule that bind. If the way in which these small fragments bind can be understood, then the chemist can design changes that merge or grow these fragments into the larger compound with the correct properties. We will use these methods to discover small molecules that change the activity of OGA and OGT. These can then be added to cells to see what effect changing the O-GlcNAc has on the way the cells behave. The principle aim is to understand the effect on cell biology, though the compounds may provide a starting place for drug design.