Thiosulfate dehydrogenase: an unusual acidophilic c-type cytochrome

有证据表明，具有不寻常的轴向组氨酸-半胱氨酸血红素铁协调的c型细胞色素在硫基能量代谢中起着关键作用。二血红素细胞色素c TsdA，作为硫代硫酸脱氢酶或连四硫酸还原酶在体内取决于宿主生物体和生长条件，最近被确定为这一令人兴奋的蛋白质组的另一个成员。虽然广泛传播，不仅在变形菌，而且在其他细菌门，详细的知识，反应机制，生物物理和结构特性，以及确切的生理作用的TsdA是不可用的。该项目旨在通过专注于两种酶的原型来填补这一空白：[1]来自紫色硫细菌Allochromatium vinosum的硫代硫酸盐脱氢酶不仅携带一个具有不寻常的轴向His/Cys配位的血红素，而且第二个血红素在还原时表现出前所未有的His/Lys到His/Met连接的血红素2。[2]来自人类肠道病原体空肠弯曲菌的双功能连四硫酸还原酶/硫代硫酸脱氢酶。这种酶似乎特别适于催化连四硫酸盐还原。结构比较表明一个血红素组的缺失/不同轴向结扎是导致这两个TsdA原型的不同性质的一个因素。与源生物体和tsdA空以及互补突变体的分子遗传学工作结合详细的生物物理学，电化学和结构表征以及两个TsdA原型的比较将回答以下问题[1]哪些是TsdA蛋白质适应的分子细节，以优先在硫代硫酸盐氧化或连四硫酸盐还原中发挥作用？[2]硫代硫酸盐脱氢酶/连四硫酸盐还原酶的生理功能和优点是什么？这些问题的答案将有助于对这种新颖而不寻常的细胞色素类型的透彻理解。此外，该项目的结果将揭示硫代硫酸盐不仅在致力于产生能量的硫代谢的细菌中，而且在与人类健康相关的硫代硫酸盐/连四硫酸盐代谢有机异养生物中的相关性。

Evidence is emerging that c-type cytochromes with an unusual axial histidine-cysteine coordination of the heme iron play a pivotal role in sulfur-based energy metabolism. The diheme cytochrome c TsdA that acts as thiosulfate dehydrogenase or tetrathionate reductase in vivo depending on the host organism and growth conditions, was recently identified as another member of this exciting group of proteins. Although wide spread not only in Proteobacteria but also in other bacterial phyla, detailed knowledge about the reaction mechanism, the biophysical and structural properties as well as the exact physiological role of TsdA is not available. This project is intended to fill this gap by focussing on two prototypes of the enzyme: [1] Thiosulfate dehydrogenase from the purple sulfur bacterium Allochromatium vinosum that does not only carry one heme with unusual axial His/Cys coordination but a second heme exhibiting an unprecedented switch of a His/Lys to His/Met ligation of heme 2 upon reduction. [2] The bifunctional tetrathionate reductase/thiosulfate dehydrogenase from the human gut pathogen Campylobacter jejuni. This enzyme appears to be especially adapted to catalyzing tetrathionate reduction. Structural comparisons indicate missing/different axial ligation of one heme group as one factor contributing to the different properties of these two TsdA prototypes. Molecular genetic work with the source organisms and tsdA null as well as complementation mutants in combination with detailed biophysical, electrochemical and structural characterization and comparison of the two TsdA prototypes will answer the following questions[1] Which are the molecular details that underlie the adaptation of TsdA proteins to function preferentially either in thiosulfate oxidation or tetrathionate reduction?[2] Which are the physiological functions and advantages of thiosulfate dehydrogenase/tetrathionate reductase? Answers to these questions will contribute to a thorough understanding of this novel and unusual type of cytochromes. Furthermore, the results of this project will shed light on the relevance of thiosulfate not only in bacteria dedicated to energy-generating sulfur metabolism but also in thiosulfate/tetrathionate metabolizing organoheterotrophs relevant to human health.