Heinzinger N K, Fujimoto S Y, Clark M A, Moreno M S, Barrett E L
Department of Food Science and Technology, University of California, Davis 95616, USA.
J Bacteriol. 1995 May;177(10):2813-20. doi: 10.1128/jb.177.10.2813-2820.1995.
The phs chromosomal locus of Salmonella typhimurium is essential for the dissimilatory anaerobic reduction of thiosulfate to hydrogen sulfide. Sequence analysis of the phs region revealed a functional operon with three open reading frames, designated phsA, phsB, and phsC, which encode peptides of 82.7, 21.3, and 28.5 kDa, respectively. The predicted products of phsA and phsB exhibited significant homology with the catalytic and electron transfer subunits of several other anaerobic molybdoprotein oxidoreductases, including Escherichia coli dimethyl sulfoxide reductase, nitrate reductase, and formate dehydrogenase. Simultaneous comparison of PhsA to seven homologous molybdoproteins revealed numerous similarities among all eight throughout the entire frame, hence, significant amino acid conservation among molybdoprotein oxidoreductases. Comparison of PhsB to six other homologous sequences revealed four highly conserved iron-sulfur clusters. The predicted phsC product was highly hydrophobic and similar in size to the hydrophobic subunits of the molybdoprotein oxidoreductases containing subunits homologous to phsA and phsB. Thus, phsABC appears to encode thiosulfate reductase. Single-copy phs-lac translational fusions required both anaerobiosis and thiosulfate for full expression, whereas multicopy phs-lac translational fusions responded to either thiosulfate or anaerobiosis, suggesting that oxygen and thiosulfate control of phs involves negative regulation. A possible role for thiosulfate reduction in anaerobic respiration was examined. Thiosulfate did not significantly augment the final densities of anaerobic cultures grown on any of the 18 carbon sources tested. on the other hand, washed stationary-phase cells depleted of ATP were shown to synthesize small amounts of ATP on the addition of the formate and thiosulfate, suggesting that the thiosulfate reduction plays a unique role in anaerobic energy conservation by S typhimurium.
鼠伤寒沙门氏菌的phs染色体位点对于将硫代硫酸盐异化厌氧还原为硫化氢至关重要。phs区域的序列分析揭示了一个功能性操纵子，其中有三个开放阅读框，分别命名为phsA、phsB和phsC，它们分别编码82.7 kDa、21.3 kDa和28.5 kDa的肽。phsA和phsB的预测产物与其他几种厌氧钼辅蛋白氧化还原酶的催化和电子传递亚基具有显著同源性，包括大肠杆菌二甲基亚砜还原酶、硝酸盐还原酶和甲酸脱氢酶。将PhsA与七种同源钼辅蛋白同时进行比较，发现在整个框架中所有八种蛋白之间有许多相似之处，因此，钼辅蛋白氧化还原酶之间存在显著的氨基酸保守性。将PhsB与其他六个同源序列进行比较，发现了四个高度保守的铁硫簇。预测的phsC产物具有高度疏水性，大小与含有与phsA和phsB同源亚基的钼辅蛋白氧化还原酶的疏水亚基相似。因此，phsABC似乎编码硫代硫酸盐还原酶。单拷贝phs-lac翻译融合体需要厌氧和硫代硫酸盐才能完全表达，而多拷贝phs-lac翻译融合体对硫代硫酸盐或厌氧均有反应，这表明phs的氧气和硫代硫酸盐控制涉及负调控。研究了硫代硫酸盐还原在厌氧呼吸中的可能作用。硫代硫酸盐并未显著提高在测试的18种碳源中的任何一种上生长的厌氧培养物的最终密度。另一方面，耗尽ATP的洗涤过的稳定期细胞在添加甲酸和硫代硫酸盐后显示能合成少量ATP，这表明硫代硫酸盐还原在鼠伤寒沙门氏菌的厌氧能量守恒中起独特作用。
