Sulfurtransferases as essential players during dissimilatory sulfur oxidation

过硫化物基团在化学上具有多种用途，并参与多种生化途径。虽然已有文献表明，过硫化蛋白为硫烷硫提供了许多重要而复杂的生物合成途径，但该项目的目的是探索硫磺转移酶催化的反应对硫磺氧化代谢的确切贡献。我们已经收集了有关硫氧化细菌细胞质中广泛存在的硫运输系统的基本信息，这些细菌追踪硫磺氧化的异化亚硫酸盐还原酶(DSR)途径。此外，我们收集了生化和生物信息学证据，指出在硫氧化原核生物中，所谓的异二硫化物还原酶(HDR)类系统是一种广泛存在的替代亚硫酸盐生成系统。硫的运输在进行这一途径的生物体中也是至关重要的，因此在异化硫氧化过程中成为一个中心和共同的元素。本项目将解决两个主要问题：(1)在通过DSR途径的蛋白质结合硫氧化过程中，确切的一系列事件是什么？类似HDR的系统真的是一个亚硫酸盐生成系统吗？硫转移反应到底是如何参与的？为了解决这些问题，蛋白质的生化特性(酶系统的体外重组、底物和产物的鉴定)、蛋白质相互作用研究和基因表达谱研究将与基因失活和互补研究(野生型、明确突变和互补突变菌株的生长实验)以及分子遗传技术相结合。遗传可及的紫色硫杆菌将作为通过DSR系统研究硫转移反应和蛋白结合硫氧化的模式生物，而硫代碱弧菌和硫螺旋体以及基因可及的脱氮α-变形杆菌将被用于阐明与HDR类系统相关的硫转移反应和蛋白结合硫的氧化。最终，我们的结果有望彻底解开发生在硫氧化原核生物中的硫转移反应网络，为过硫基生物化学增加新的反应和蛋白质，并阐明硫氧化的新途径。

Persulfide groups are chemically versatile and participate in a wide array of biochemical pathways. Whilst it is well documented that persulfurated proteins supply a number of important and elaborate biosynthetic pathways with sulfane sulfur, this project aims at exploring the exact contribution of sulfurtransferase-catalyzed reactions to oxidative sulfur metabolism. We already collected basic information on the extensive sulfur-trafficking system occurring in the cytoplasm of sulfur oxidizing bacteria pursuing the Dsr (dissimilatory sulfite reductase) pathway of sulfur oxidation. In addition, we gathered biochemical and bioinformatic evidence pointing at the so-called heterodisulfide-reductase (Hdr) -like system as a wide-spread alternative sulfite-generating system in sulfur-oxidizing prokaryotes. Sulfur-trafficking was established to also be of pivotal importance in organisms pursuing this pathway and thus emerges as a central and common element during dissimilatory sulfur oxidation. The present project will address two major questions: (1.) What is the exact series of events during protein-bound sulfur oxidation via the Dsr pathway? (2.) Does the Hdr-like system indeed work a sulfite-generating system and how exactly are sulfur transfer reactions involved? To solve these questions, biochemical characterization of proteins (reconstitution of enzyme systems in vitro, identification of substrates and products), protein interaction studies, and gene expression profiling will be combined with gene inactivation and complementation studies (growth experiments with wild type, defined mutant and complemented mutants strains) as well as with molecular genetic techniques. The genetically accessible purple sulfur bacterium Allochromatium vinosum will serve as the model organism for the studies on sulfur transfer reactions and oxidation of protein-bound sulfur via the Dsr system, while Thioalkalivibrio and Thiorhdospira species as well as the genetically accessible Alphaproteobacterium Hyphomicrobium denitrificans will be used for elucidating sulfur transfer reactions and oxidation of protein-bound sulfur associated with the Hdr-like system. Ultimately, our results are expected to completely unravel the networks of sulfur transfer reactions occurring in sulfur oxidizing prokaryotes, to add new reactions and proteins to persulfide group biochemistry and to clarify a new pathway of sulfur oxidation.