Acid stress is an environmental problem for plants and fresh water cyanobacteria like the filamentous, heterocyst forming species Anabaena sp. PCC 7120 (hereafter Anabaena sp.). Heterocyst differentiation, cell–cell communication and nitrogen fixation has been deeply studied in this model organism, but little is known about the cellular response of Anabaena sp. to decreased pH values, causing acid stress. ATP-binding cassette (ABC) transporters are involved in acid stress response in other bacteria, by exporting proteins responsible for survival under acidification. The genome of Anabaena sp. encodes numerous ABC transporter components, whose function is not known yet. Here, we describe the function of the gene all5304 encoding a protein with homology to membrane fusion proteins of tripartite efflux pumps driven by ABC transporters like HlyBD-TolC of Escherichia coli. The all5304 mutant shows less resistance against low pH, even though the expression of the gene is independent from the pH of the medium. We compared the exoproteome of the wild type and mutant cultures and identified three proteins-candidate substrates of the putative transporter. Including the in silico analysis of All5304, our results suggest that All5304 functions as part of an efflux pump, secreting of a protein necessary for acid tolerance in Anabaena sp.

中文翻译：

---

类HlyD的膜融合蛋白All5304对于丝状蓝细菌鱼腥藻的酸胁迫存活至关重要。PCC 7120。

酸胁迫是植物和淡水蓝细菌（如丝状，形成异囊藻的物种Anabaena sp。）的环境问题。PCC 7120（以下称为Anabaena sp。）。在这种模式生物中，已经深入研究了异质囊分化，细胞间通讯和固氮作用，但对鱼腥藻的细胞反应了解甚少。降低pH值，引起酸胁迫。ATP结合盒（ABC）转运蛋白通过输出负责在酸化条件下存活的蛋白质，参与其他细菌的酸胁迫反应。鱼腥藻的基因组。编码许多ABC转运蛋白成分，其功能尚不清楚。在这里，我们描述了all5304基因的功能编码与ABC转运蛋白（如大肠杆菌HlyBD-TolC）驱动的三方外排泵的膜融合蛋白具有同源性的蛋白。所述all5304对低pH的突变体显示较小的阻力，即使基因的表达独立于介质的pH。我们比较了野生型和突变体培养的外蛋白质组，并确定了推定转运蛋白的三种蛋白质候选底物。包括在硅片All5304的分析，我们的研究结果表明，All5304用作外排泵的一部分，分泌必需的耐酸性蛋白质的鱼腥藻。