Department of Microbiology/Organismic Interactions, IMIT - Institute of Microbiology and Infection Medicine Tübingen, University of Tübingen, 72076 Tübingen, Germany.
Microbiology (Reading). 2012 Oct;158(Pt 10):2537-2545. doi: 10.1099/mic.0.058909-0. Epub 2012 Aug 2.
Efflux pumps export a wide variety of proteinaceous and non-proteinaceous substrates across the Gram-negative cell wall. For the filamentous cyanobacterium Anabaena sp. strain PCC 7120, the ATP-driven glycolipid efflux pump DevBCA-TolC has been shown to be crucial for the differentiation of N(2)-fixing heterocysts from photosynthetically active vegetative cells. In this study, a homologous system was described. All0809/8/7-TolC form a typical ATP-driven efflux pump as shown by surface plasmon resonance. This putative exporter is also involved in diazotrophic growth of Anabaena sp. PCC 7120. A mutant in all0809 encoding the periplasmic membrane fusion protein of the pump was not able to grow without combined nitrogen. Although heterocysts of this mutant were not distinguishable from those of the wild-type in light and electron micrographs, they were impaired in providing the microoxic environment necessary for N(2) fixation. RT-PCR of all0809 transcripts and localization studies on All0807-GFP revealed that All0809/8/7 was initially downregulated during heterocyst maturation and upregulated at later stages of heterocyst formation in all cells of the filament. A substrate of the efflux pump could not be identified in ATP hydrolysis assays. We discuss a role for All0809/8/7-TolC in maintaining the continuous periplasm and how this would be of special importance for heterocyst differentiation.
外排泵将各种蛋白质和非蛋白质底物输出革兰氏阴性细胞壁。对于丝状蓝藻鱼腥藻 PCC 7120，已证明 ATP 驱动的糖脂外排泵 DevBCA-TolC 对于从光合作用活性营养细胞分化 N(2)-固定异形胞至关重要。在这项研究中，描述了一个同源系统。All0809/8/7-TolC 形成了典型的 ATP 驱动的外排泵，如表面等离子体共振所示。这种假定的外排泵还参与鱼腥藻 PCC 7120 的固氮生长。编码泵周质膜融合蛋白的 all0809 突变体在没有结合氮的情况下无法生长。尽管该突变体的异形胞在光和电子显微镜下与野生型异形胞无法区分，但它们在提供 N(2)固定所需的微氧环境方面存在缺陷。All0809 转录物的 RT-PCR 和 All0807-GFP 的定位研究表明，All0809/8/7 在异形胞成熟过程中最初下调，在丝状藻所有细胞的异形胞形成的后期上调。在 ATP 水解测定中未鉴定出外排泵的底物。我们讨论了 All0809/8/7-TolC 在维持连续周质中的作用，以及这对异形胞分化的特殊重要性。
