Abstract：
Nitric oxide (·NO) is a prevalent antimicrobial that is known to damage iron-containing enzymes in amino acid (AA) biosynthesis pathways. With Escherichia coli, ·NO is detoxified in aerobic environments by Hmp, which is an enzyme that is synthesized de novo in response to ·NO. With this knowledgebase, it is expected that the availability of AAs in the extracellular environment would enhance ·NO detoxification, because AAs would foster translation of Hmp. However, we observed that ·NO detoxification by E. coli was far slower in populations grown and treated in the presence of AAs (AA+) in comparison to those grown and stressed in the absence of AAs (AA-). Further experiments revealed that AA+ populations had difficulty translating proteins under ·NO stress, and that ·NO activated the stringent response in AA+ populations. Additional work revealed significant ATP depletion in ·NO-stressed AA+ cultures that far exceeded that of ·NO-stressed AA- populations. Transcription, translation, and RelA were not found to be significant contributors to the ATP depletion observed, whereas AA import was implicated as a significant ATP consumption pathway. Alleviating ATP depletion while maintaining access to AAs partially restored ·NO detoxification, which suggested that ATP depletion contributed to the translational difficulties observed in ·NO-stressed AA+ populations. These data reveal an unexpected interaction within the ·NO response network of E. coli that stimulates a stringent response by RelA in conditions where AAs are plentiful.
摘要：
一氧化氮（·NO）是一种常见的抗微生物剂，已知会破坏氨基酸（AA）生物合成途径中的含铁酶。用大肠杆菌，·NO在有氧环境中被Hmp解毒，这是一种响应·NO从头合成的酶。有了这个知识库，预计在细胞外环境中AAs的可用性将增强·NO解毒，因为AA会促进HMP的翻译。然而,我们观察到，在存在AA（AA）的情况下生长和处理的种群中，与在不存在AA（AA-）的情况下生长和应激的种群相比，大肠杆菌的·NO解毒要慢得多。进一步的实验表明，AA+群体在·NO胁迫下难以翻译蛋白质，并且·NO激活了AA+群体中的严格反应。其他工作显示，在·NO胁迫的AA培养物中，ATP的消耗显着，远远超过了·NO胁迫的AA-种群。转录,翻译,和RelA没有发现是观察到的ATP耗竭的重要贡献者，而AA进口被认为是一个重要的ATP消耗途径。缓解ATP消耗，同时保持获得部分恢复的AA·NO解毒，这表明ATP耗竭导致了在·NO胁迫的AA种群中观察到的翻译困难。这些数据揭示了大肠杆菌的·NO响应网络内的意外相互作用，该相互作用在AA丰富的条件下刺激RelA的严格响应。
