Two TonB-dependent outer membrane transporters involved in heme uptake in Anabaena sp. PCC 7120.

IF 4.1 3区 生物学 Q2 CELL BIOLOGY Microbial Cell Pub Date : 2024-01-09 eCollection Date: 2024-01-01 DOI:10.15698/mic2024.01.812
Julia Graf, Martin Schöpperle, Rafael Pernil, Enrico Schleiff
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Abstract

Low availability of micronutrients such as iron has enforced the evolution of uptake systems in all kingdoms of life. In Gram-negative bacteria, outer membrane, periplasmatic and plasma membrane localized proteins facilitate the uptake of iron-loaded chelators, which are energized by TonB proteins. The specificity of different uptake systems likely depends either on the endogenously produced siderophore or on the bioavailability of iron-chelator complexes in the environment. Hence, an uptake system for schizokinen produced by the model cyanobacterium Anabaena sp. PCC 7120 exists, while bioinformatics analysis suggests the existence of additional systems, likely for uptake of xenosiderophores. Consistently, proteins encoded by alr2153 (hutA1) and alr3242 (hutA2) are assigned as outer membrane heme transporters. Indeed, Anabaena sp. PCC 7120 can utilize external heme as an iron source. The addition of heme resulted in an induction of genes involved in heme degradation and chlorophyll a synthesis and in an increase of the chlorophyll a content. Moreover, iron starvation induced the expression of hutA1, while the addition of heme led to its repression. Remarkably, the addition of a high concentration of heme but not iron starvation resulted in hutA2 induction. Plasmid insertion mutants of both genes exhibited a reduced capacity to recover from iron starvation by heme addition, which indicates a dependence of heme uptake on functional HutA1 and HutA2 proteins. The structural model generated by bioinformatics methods is further in agreement with a role in heme uptake. Thus, we provide evidence that Anabaena sp. PCC 7120 uses a heme uptake system in parallel to other iron acquisition systems.

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Anabaena sp. PCC 7120 中参与血红素吸收的两个依赖于 TonB 的外膜转运体。
由于铁等微量营养元素的供应量较低,所有生物界都在不断进化吸收系统。在革兰氏阴性细菌中,外膜、质粒周围和质粒膜定位蛋白促进了铁螯合剂的吸收,TonB 蛋白则为其提供能量。不同摄取系统的特异性可能取决于内源产生的铁螯合剂或环境中铁螯合剂复合物的生物利用率。因此,模式蓝藻 Anabaena sp. PCC 7120 产生的裂殖素的摄取系统是存在的,而生物信息学分析表明还存在其他系统,可能用于摄取异苷酸。同样,alr2153(hutA1)和 alr3242(hutA2)编码的蛋白质被认为是外膜血红素转运体。事实上,Anabaena sp.添加血红素会诱导参与血红素降解和叶绿素 a 合成的基因,并增加叶绿素 a 的含量。此外,铁饥饿会诱导 hutA1 的表达,而添加血红素则会抑制其表达。值得注意的是,添加高浓度血红素而不是铁饥饿会诱导 hutA2 的表达。这两个基因的质粒插入突变体通过添加血红素从铁饥饿中恢复的能力都有所下降,这表明血红素吸收依赖于功能性 HutA1 和 HutA2 蛋白。通过生物信息学方法生成的结构模型进一步证实了其在血红素吸收中的作用。因此,我们提供的证据表明,Anabaena sp.
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来源期刊
Microbial Cell
Microbial Cell Multiple-
CiteScore
6.40
自引率
0.00%
发文量
32
审稿时长
12 weeks
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