Enzymes of the microbial catabolism of the thioether 3,3´-thiodipropionic acid

拟议的项目调查了有机硫化合物和硫醚3，3‘-硫代二丙酸(TDP)作为唯一碳源的罕见微生物降解。以前分离到的奇异变色杆菌菌株TBEA6是研究TDP分解代谢的最有利的候选菌株，它作为模式生物被应用于本项目。大多数基因及其翻译产物可能与TDP的分解代谢途径有关，这些基因及其翻译产物是我们实验室以前发现的。这一途径的关键酶--3-硫代丙酸双加氧酶(MDO)的详细生化特征已经完成。MDO催化上述途径的第二步，即3-巯基丙酸酯(3MP)的巯基氧化成亚磺基，从而生成3-磺酰丙酸酯。然而，重要的初始步骤，即TDP进入细胞并随后将TDP裂解成3-羟基丙酸和3MP，目前还只是推测。假设的运输系统属于TTT(三方三羧酸盐运输)家族。TDP裂解酶是一种新型的依赖FAD的氧化还原酶。这些反应是这个项目的主要焦点。此外，还将详细研究中间体3-磺基丙酸在辅酶A连接酶催化下活化为3-磺基丙酰-辅酶A，以及随后由酰基-辅酶A脱氢酶类脱硫酶进行的脱硫反应。因此，在该项目期间，将发展和优化体内和体外酶分析方法(I)。此外，Göttingen基因组实验室(G2L)已对反常弧菌TBEA6株的全基因组DNA进行了测序，并将对其进行加工和注释(II)。随后，将完成在TDP和替代碳源上生长过程中的蛋白质组研究(III)。这些发现将用于以无毒前体TDP为基础的多硫酯的强化生物技术生产。

The proposed project investigates the rare microbial degradation of the organic sulfur compound and thioether 3,3´-thiodipropionic acid (TDP) as sole carbon source. The previously isolated beta-proteobacterium Variovorax paradoxus strain TBEA6 is the most favourable candidate to elucidate TDP catabolism of TDP; it serves as a model organism and is employed in this project. Most genes and their translational products, which are putatively involved in the catabolic pathway of TDP, were previously identified by our laboratory. A detailed biochemical characterization of the key enzyme of this pathway, the 3-mercaptopropionate dioxygenase (Mdo), was already done. Mdo catalyzes the second step of the proposed pathway, the oxidation of the sulfhydryl group of 3-mercaptopropionate (3MP) into a sulfino group, thereby forming 3-sulfinopropionate. However, the important initial steps, i. e. the transport of TDP into the cell and its subsequent cleavage of TDP into 3-hydroxypropionic acid and 3MP, are only suppositions, yet. The assumed transport system belongs to the TTT (Tripartite Tricarboxylate Transport) family. The enzyme putatively responsible for the cleavage of TDP is a novel FAD-dependent oxidoreductase. These reactions are in the major focus of this project. In addition, the proposed activation of the intermediate 3-sulfinopropionic acid into 3-sulfinopropionyl-CoA, which is catalyzed by a CoA ligase, and the subsequent desulfination reaction performed by an acyl-CoA dehydrogenase-like desulfinase will be investigated in detail. Thus, during this project in vitro and in vivo enzyme assays will be developed and optimized (i). Moreover, the whole-genome DNA of V. paradoxus strain TBEA6 was sequenced by the Göttingen Genomics Laboratory (G2L), and will be processed and annotated (ii). Subsequently, proteome studies during growth on TDP and alternative carbon sources will be accomplished (iii). The findings will be used for the enhanced biotechnological production of polythioesters based on the nontoxic precursor TDP.