NhaD type sodium/proton-antiporter of Halomonas elongata: a salt stress response mechanism in marine habitats?
NhaD type sodium/proton-antiporter of Halomonas elongata: a salt stress response mechanism in marine habitats?
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DOI：
10.1186/1746-1448-2-10
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发表时间：
2006-07-27
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影响因子：
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通讯作者：
Galinski EA
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作者：
Kurz M;Brünig AN;Galinski EA
钠/质子反向转运蛋白（Nha）在pH和Na+稳态中起重要作用。在微生物中存在对Na+和Li+具有不同能力、亲和力和选择性的几种类型。E.大肠杆菌NhaA和NhaB的Na+/H+反向转运蛋白已得到充分研究，但其他类型的Na+/H+反向转运蛋白（如NhaD）的功能尚未完全了解。由于几种反向转运蛋白在高等生物的生理学中的不同点发挥着重要作用，因此可以推测其中一些原核反向转运蛋白的主要功能不同于pH-和Na+-稳态。本研究探讨了在嗜盐真杆菌长盐单胞菌中发现的编码NhaD型反向转运蛋白的基因的功能和调控。该基因的一级氨基酸序列与已知的解淀粉Alkalimonasamylolytica、Shewanellaoneidensis等海洋生物的NhaD型反向转运蛋白的同源性均在60%以上。发现了H. elongata NhaD表达。克隆了该基因，并在E.杆菌反向转运蛋白缺陷型NaCl和LiCl敏感型E.大肠杆菌突变体EP 432和KNabc被携带H. nhaD基因。令人惊讶的是，E.大肠杆菌DH 5 α具有完整的内稳态系统，共表达NhaD后，其内稳态系统的稳定性提高。由于NhaD是迄今为止只从嗜盐或嗜盐嗜碱变形菌中发现的反向转运蛋白，因此可以推测这种类型的反向转运蛋白提供了一种适应海洋生境的特殊机制。正如已经推测的那样（尽管没有支持性数据），并在本研究中得到证实，这可能是出于药物监管目的的主动Na+输入。
Sodium/proton-antiporters (Nha) are known to play an important role in pH- and Na+-homeostasis. In microorganisms several types with different capacity, affinity and selectivity for Na+ and Li+ exist. The homeostasis system of E. coli, NhaA and NhaB, is well researched, but the function of other types of Na+/H+-antiporters like NhaD is yet to be fully understood. Since several antiporters play an important role at various points in the physiology of higher organisms, one can speculate that the main functions of some of those procaryotic antiporters differ from pH- and Na+-homeostasis. This study investigates the function and regulation of a gene encoding for a NhaD type antiporter which was discovered in the halophilic eubacterium Halomonas elongata. The deduced primary amino acid sequence of the abovementioned gene showed more than 60% identity to known antiporters of the NhaD type from Alkalimonas amylolytica, Shewanella oneidensis and several other marine organisms of the γ-Proteobacteria. Evidence was found for a dual regulation of H. elongata NhaD expression. The gene was cloned and expressed in E. coli. Antiporter deficient NaCl and LiCl sensitive E. coli mutants EP432 and KNabc were partially complemented by a plasmid carrying the H. elongata nhaD gene. Surprisingly the LiCl sensitivity of E. coli strain DH5α having a complete homeostasis system was increased when NhaD was co-expressed. Since NhaD is an antiporter known so far only from halophilic or haloalcaliphilic Proteobacteria one can speculate that this type of antiporter provides a special mechanism for adaptation to marine habitats. As was already speculated – though without supporting data – and substantiated in this study this might be active Na+-import for osmoregulatory purposes.