Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, People's Republic of China.
Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA.
Appl Environ Microbiol. 2018 May 1;84(10). doi: 10.1128/AEM.00110-18. Print 2018 May 15.
is generally regarded as a moderately salt- and alkali-tolerant industrial organism. However, relatively little is known about the molecular mechanisms underlying these specific adaptations. Here, we found that the Mrp1 antiporter played crucial roles in conferring both environmental Na resistance and alkali tolerance whereas the Mrp2 antiporter was necessary in coping with high-KCl stress at alkaline pH. Furthermore, the Δ Δ double mutant showed the most-severe growth retardation and failed to grow under high-salt or alkaline conditions. Consistent with growth properties, the Na/H antiporters of were differentially expressed in response to specific salt or alkaline stress, and an alkaline stimulus particularly induced transcript levels of the Mrp-type antiporters. When the major Mrp1 antiporter was overwhelmed, might employ alternative coordinate strategies to regulate antiport activities. Site-directed mutagenesis demonstrated that several conserved residues were required for optimal Na resistance, such as Mrp1A K, Mrp1C I, Mrp1A H, and Mrp1D E Moreover, the chromosomal replacement of lysine 299 in the Mrp1A subunit resulted in a higher intracellular Na level and a more alkaline intracellular pH value, thereby causing a remarkable growth attenuation. Homology modeling of the Mrp1 subcomplex suggested two possible ion translocation pathways, and lysine 299 might exert its effect by affecting the stability and flexibility of the cytoplasm-facing channel in the Mrp1A subunit. Overall, these findings will provide new clues to the understanding of salt-alkali adaptation during stress acclimatization. The capacity to adapt to harsh environments is crucial for bacterial survival and product yields, including industrially useful Although exhibits a marked resistance to salt-alkaline stress, the possible mechanism for these adaptations is still unclear. Here, we present the physiological functions and expression patterns of putative Na/H antiporters and conserved residues of Mrp1 subunits, which respond to different salt and alkaline stresses. We found that the Mrp-type antiporters, particularly the Mrp1 antiporter, played a predominant role in maintaining intracellular nontoxic Na levels and alkaline pH homeostasis. Loss of the major Mrp1 antiporter had a profound effect on gene expression of other antiporters under salt or alkaline conditions. The lysine 299 residue may play its essential roles in conferring salt and alkaline tolerance by affecting the ion translocation channel of the Mrp1A subunit. These findings will contribute to a better understanding of Na/H antiporters in sodium antiport and pH regulation.
被普遍认为是一种中度耐盐和耐碱的工业生物。然而，对于这些特定适应的分子机制，我们知之甚少。在这里，我们发现 Mrp1 反向转运蛋白在赋予环境 Na 抗性和耐碱能力方面发挥了关键作用，而 Mrp2 反向转运蛋白在碱性 pH 下应对高 KCl 应激是必要的。此外，ΔΔ双突变体表现出最严重的生长迟缓，无法在高盐或碱性条件下生长。与生长特性一致，的 Na/H 反向转运蛋白在响应特定盐或碱性应激时表现出不同的表达，而碱性刺激特别诱导了 Mrp 型反向转运蛋白的转录水平。当主要的 Mrp1 反向转运蛋白过载时，可能会采用替代的协调策略来调节反向转运活性。定点突变表明，几个保守残基对于最佳的 Na 抗性是必需的，如 Mrp1A K、Mrp1C I、Mrp1A H 和 Mrp1D E。此外，Mrp1A 亚基中赖氨酸 299 的染色体替换导致细胞内 Na 水平升高和细胞内 pH 值升高，从而导致显著的生长衰减。Mrp1 亚复合物的同源建模表明了两种可能的离子转运途径，赖氨酸 299 可能通过影响 Mrp1A 亚基细胞质面向通道的稳定性和灵活性来发挥作用。总的来说，这些发现将为理解 在胁迫适应过程中的盐碱性适应提供新的线索。适应恶劣环境的能力对细菌的生存和产品产量至关重要，包括工业上有用的。尽管 表现出对盐碱性胁迫的显著抗性，但这些适应的可能机制仍不清楚。在这里，我们介绍了 假定的 Na/H 反向转运蛋白和 Mrp1 亚基保守残基的生理功能和表达模式，它们对不同的盐和碱性应激做出响应。我们发现，Mrp 型反向转运蛋白，特别是 Mrp1 反向转运蛋白，在维持细胞内无毒 Na 水平和碱性 pH 稳态方面发挥着主要作用。在盐或碱性条件下，主要 Mrp1 反向转运蛋白的缺失对其他反向转运蛋白的基因表达有深远的影响。赖氨酸 299 残基可能通过影响 Mrp1A 亚基的离子转运通道，在赋予耐盐和耐碱性方面发挥着重要作用。这些发现将有助于更好地理解 Na/H 反向转运蛋白在钠反向转运和 pH 调节中的作用。
