Biochemistry and molecular physiology of the protein ABA3

本项目的目的是研究拟南芥调控蛋白ABA3的详细功能。在我们之前的工作中，我们已经证明ABA3催化一种新型的翻译后蛋白质修饰：硫化激活。ABA3是一种钼辅酶硫化酶，它能激活两种含钼的酶：醛氧化酶(AO)和黄嘌呤脱氢酶(XDH)。AO催化脱落酸(ABA)生物合成的最后一步，而AO和XDH都产生ROS。在ABA3蛋白的催化下，通过改变ABA和ROS分子的活性和失活比例，可以迅速提高ABA和ROS的浓度。-这个项目的目的有两个：在第一部分，我们想要描述ABA3催化的调节性硫转移的详细反应机理。这种分子内和分子间硫转移的反应步骤是新的，没有先例。因此，它将成为其他团队破译这种翻译后激活反应的原型，在哺乳动物、低等真核生物和细菌中，对此一无所知。在第二部分中，我们打算阐明ABA3的生理作用，同时我们课题组已经开发了一些工具和分析方法来研究低丰度蛋白ABA3的表达和活性。我们想要说明ABA3的哪些功能与AO和XDH的激活有关，哪些功能与AO/XDH的激活无关。在此背景下，我们将分析ABA3的选择性剪接和核定位的重要性，我们已经有了第一个实验适应症。

It is the aim of this project to study the detailed function of the Arabidopsis regulatory protein ABA3. In our previous work, we have shown that ABA3 catalyzes a novel type of posttranslational protein modification: activation by sulfuration. ABA3 is a molybdenum cofactorsulfurase that activates the two Mo-containing enzymes aldehyde oxidase (AO) and xanthine dehydrogenase (XDH). AO catalyzes that last step of abscisic acid (ABA) biosynthesis, and both AO and XDH produce ROS. The concentration of ABA and ROS can be rapidly increased by changing the ratio between inactive and active XDH and AO molecules, as catalyzed by the ABA3 protein. - The aim of this project is twofold: In the first part we want to delineate the detailed reaction mechanism of regulatory sulfur transfer catalyzed by ABA3. This sequence of reaction steps of intra- and intermolecular sulfur-transfer is novel and has no precedent. Thus it will constitute the prototype for other groups to decipher this kind of post-translational activation reactions in mammals, lower eukaryotes and bacteria where nothing is known about it. In the second part, we intend to clarify the physiological role of ABA3 as meanwhile a number of tools and assays has been worked out in our group for studying expression and activity of the low-abundant protein ABA3. We want to show which functions of ABA3 are related to the activation of AO and XDH and which functions are not connected to the activation of AO/XDH. In this context, we will analyze the importance of alternative splicing and of nuclear localization of ABA3 for which we have first experimental indications.