Activity of Spore-Specific Respiratory Nitrate Reductase 1 of Streptomyces coelicolor A3(2) Requires a Functional Cytochrome bcc-aa3 Oxidase Supercomplex
Activity of Spore-Specific Respiratory Nitrate Reductase 1 of Streptomyces coelicolor A3(2) Requires a Functional Cytochrome bcc-aa3 Oxidase Supercomplex
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DOI：
10.1128/jb.00104-19
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发表时间：
2019-06-01
影响因子：
3.2
通讯作者：
Sawers, R. Gary
中科院分区：
文献类型：
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作者：
Falke, Doerte;Biefel, Bianca;Sawers, R. Gary
孢子的代谢活性大大降低，是在放线菌的复杂发育周期中产生的。休眠的孢子可以存活数十年，但人们对它们如何保存能量知之甚少。然而，已知它们可以利用内源性电子源还原氧或硝酸盐。S. coelicolor使用细胞色素bd氧化酶或细胞色素bcc-aa(3)氧化酶超络合物还原氧，而硝酸通过na型硝酸还原酶还原，通常直接氧化喹啉。在这里，我们发现在休眠孢子中，Nar1硝酸盐还原酶需要一个功能性的bcc-aa(3)超络合物来还原硝酸盐。缺乏编码bcc-aa(3)超复合体的完整qcr-cta遗传位点的突变体没有表现出nar1依赖性的硝酸盐还原。Nar1活性的恢复是通过遗传互补实现的，但只有在将完整的qcr-cta位点重新引入突变菌株时才能实现。我们可以排除超络合物对硝酸盐还原的依赖是通过调节硝酸盐的运输。此外，在qcr-cta突变体中合成了Nar1的催化亚基NarG1，排除了转录控制的可能性。在菌丝体中组成性合成Nar1表明该酶在该室中活性较低，表明Nar1酶不能作为典型的喹啉氧化酶。值得注意的是，在菌丝生长过程中具有活性的Nar2酶对硝酸盐的还原并不完全依赖于bcc-aa(3)超络合物的活性。总之，我们的数据表明，Nar1与质子转移的bcc-aa(3)超复合体一起起作用，以提高休眠孢子的能量保存效率。重要性：青色链霉菌形成孢子，仅使用内源性电子供体与氧气或硝酸盐呼吸。这有助于维持膜电位，从而维持膜的生存能力。呼吸硝酸还原酶（Nar）通常直接从被还原的醌类中接受电子；然而，我们发现孢子中的硝酸盐呼吸需要一个由细胞色素BCC氧化还原酶和aa(3)氧化酶组成的呼吸超复合体。我们的研究结果表明，nnal酶与质子易位的bcc-aa(3)超复合体一起作用，有助于更有效地维持膜电位。剖析这种生存策略背后的机制对于我们了解细菌在感染过程中的持久性以及细菌如何应对自然环境中的营养限制非常重要。
Spores have strongly reduced metabolic activity and are produced during the complex developmental cycle of the actinobacterium Streptomyces coelicolor. Resting spores can remain viable for decades, yet little is known about how they conserve energy. It is known, however, that they can reduce either oxygen or nitrate using endogenous electron sources. S. coelicolor uses either a cytochrome bd oxidase or a cytochrome bcc-aa(3) oxidase supercomplex to reduce oxygen, while nitrate is reduced by Nar-type nitrate reductases, which typically oxidize quinol directly. Here, we show that in resting spores the Nar1 nitrate reductase requires a functional bcc-aa(3) supercomplex to reduce nitrate. Mutants lacking the complete qcr-cta genetic locus encoding the bcc-aa(3) supercomplex showed no Nar1-dependent nitrate reduction. Recovery of Nar1 activity was achieved by genetic complementation but only when the complete qcr-cta locus was reintroduced to the mutant strain. We could exclude that the dependence on the supercomplex for nitrate reduction was via regulation of nitrate transport. Moreover, the catalytic subunit, NarG1, of Nar1 was synthesized in the qcr-cta mutant, ruling out transcriptional control. Constitutive synthesis of Nar1 in mycelium revealed that the enzyme was poorly active in this compartment, suggesting that the Nar1 enzyme cannot act as a typical quinol oxidase. Notably, nitrate reduction by the Nar2 enzyme, which is active in growing mycelium, was not wholly dependent on the bcc-aa(3) supercomplex for activity. Together, our data suggest that Nar1 functions together with the proton-translocating bcc-aa(3) supercomplex to increase the efficiency of energy conservation in resting spores.IMPORTANCE Streptomyces coelicolor forms spores that respire with either oxygen or nitrate, using only endogenous electron donors. This helps maintain a membrane potential and, thus, viability. Respiratory nitrate reductase (Nar) usually receives electrons directly from reduced quinone species; however, we show that nitrate respiration in spores requires a respiratory supercomplex comprising cytochrome bcc oxidoreductase and aa(3) oxidase. Our findings suggest that the Narl enzyme in the S. coelicolor spore functions together with the proton-translocating bcc-aa(3) supercomplex to help maintain the membrane potential more efficiently. Dissecting the mechanisms underlying this survival strategy is important for our general understanding of bacterial persistence during infection processes and of how bacteria might deal with nutrient limitation in the natural environment.