Functional Dependence between Septal Protein SepJ from Anabaena sp. Strain PCC 7120 and an Amino Acid ABC-Type Uptake Transporter
Functional Dependence between Septal Protein SepJ from Anabaena sp. Strain PCC 7120 and an Amino Acid ABC-Type Uptake Transporter
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DOI：
10.1128/jb.00289-15
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发表时间：
2015-06
影响因子：
3.2
通讯作者：
L. Escudero;Vicente Mariscal;E. Flores
中科院分区：
文献类型：
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作者：
L. Escudero;Vicente Mariscal;E. Flores
在形成异形胞的蓝藻固氮丝状体中，两种不同的细胞类型，固定CO2的营养细胞和固定N2的异形胞，交换营养物质，包括一些氨基酸。在模式生物鱼腥藻属菌株PCC 7120中，由周质和完整膜（通透酶）部分组成的SepJ蛋白位于连接细丝中相邻细胞的细胞间隔膜处。单细胞蓝细菌细长聚球藻菌株PCC 7942具有编码与SepJ通透酶结构域同源的通透酶的基因Synpcc 7942_1024（此处指定为dmeA）。构建了缺乏dmeA或缺乏dmeA并表达鱼腥藻sepJ的聚球藻菌株。聚球藻dmeA突变体表现出一个显着的22%至32%的天冬氨酸，谷氨酸和谷氨酰胺的吸收，表型，可以部分补充鱼腥藻sepJ。聚球藻突变体的ATP结合盒（ABC）型转运蛋白的极性氨基酸显示>98%的谷氨酸的摄取减少，无论是否存在的dmeA或鱼腥藻sepJ在同一菌株。因此，需要聚球藻DmeA或鱼腥藻SepJ来观察ABC转运蛋白的完全（或接近完全）活性。鱼腥藻sepJ缺失突变体谷氨酸和天冬氨酸的摄取，这也需要在这个蓝藻的活性的ABC型转运蛋白的极性氨基酸显着受损。因此，SepJ似乎一般刺激活性的蓝藻ABC型转运蛋白的极性氨基酸。相反，鱼腥藻突变体的三个ABC型转运氨基酸受损的5-羧基荧光素，SepJ相关的属性的细胞间转移。我们的研究结果揭示了可能的功能相互作用的重要重氮营养生长的运输元素。膜转运蛋白对于细胞生命的许多方面都是必不可少的，从单细胞生物中物质的摄取和输出到多细胞生物中的细胞间分子交换。形成异型囊的蓝藻，如鱼腥藻，代表了一种独特的多细胞性，其中两种细胞类型交换营养物质和调节剂。SepJ蛋白位于鱼腥藻丝状体的细胞间隔膜处，含有药物/代谢物转运蛋白（DMT）超家族的通透酶结构域，该结构域以某种方式有助于细胞间分子转移。在这项工作中，我们发现SepJ刺激ATP结合盒（ABC）超家族的极性氨基酸摄取转运蛋白的活性，其本身可能影响与SepJ相关的细胞间转移活性，从而揭示这些不同转运蛋白之间可能的功能相互作用。
ABSTRACT In the diazotrophic filaments of heterocyst-forming cyanobacteria, two different cell types, the CO2-fixing vegetative cells and the N2-fixing heterocysts, exchange nutrients, including some amino acids. In the model organism Anabaena sp. strain PCC 7120, the SepJ protein, composed of periplasmic and integral membrane (permease) sections, is located at the intercellular septa joining adjacent cells in the filament. The unicellular cyanobacterium Synechococcus elongatus strain PCC 7942 bears a gene, Synpcc7942_1024 (here designated dmeA), encoding a permease homologous to the SepJ permease domain. Synechococcus strains lacking dmeA or lacking dmeA and expressing Anabaena sepJ were constructed. The Synechococcus dmeA mutant showed a significant 22 to 32% decrease in the uptake of aspartate, glutamate, and glutamine, a phenotype that could be partially complemented by Anabaena sepJ. Synechococcus mutants of an ATP-binding-cassette (ABC)-type transporter for polar amino acids showed >98% decreased uptake of glutamate irrespective of the presence of dmeA or Anabaena sepJ in the same strain. Thus, Synechococcus DmeA or Anabaena SepJ is needed to observe full (or close to full) activity of the ABC transporter. An Anabaena sepJ deletion mutant was significantly impaired in glutamate and aspartate uptake, which also in this cyanobacterium requires the activity of an ABC-type transporter for polar amino acids. SepJ appears therefore to generally stimulate the activity of cyanobacterial ABC-type transporters for polar amino acids. Conversely, an Anabaena mutant of three ABC-type transporters for amino acids was impaired in the intercellular transfer of 5-carboxyfluorescein, a SepJ-related property. Our results unravel possible functional interactions in transport elements important for diazotrophic growth. IMPORTANCE Membrane transporters are essential for many aspects of cellular life, from uptake and export of substances in unicellular organisms to intercellular molecular exchange in multicellular organisms. Heterocyst-forming cyanobacteria such as Anabaena represent a unique case of multicellularity, in which two cell types exchange nutrients and regulators. The SepJ protein located at the intercellular septa in the filaments of Anabaena contains a permease domain of the drug/metabolite transporter (DMT) superfamily that somehow contributes to intercellular molecular transfer. In this work, we have found that SepJ stimulates the activity of a polar amino acid uptake transporter of the ATP-binding-cassette (ABC) superfamily, which could itself affect an intercellular transfer activity related to SepJ, thus unraveling possible functional interactions between these different transporters.