Molybdate transport and its effect on nitrogen utilization in the cyanobacterium Anabaena variabilis ATCC 29413
Molybdate transport and its effect on nitrogen utilization in the cyanobacterium Anabaena variabilis ATCC 29413
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DOI：
10.1046/j.1365-2958.2003.03851.x
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发表时间：
2004-01
影响因子：
3.6
通讯作者：
M. Zahalak;Brenda S. Pratte;Kelly Werth;T. Thiel
中科院分区：
文献类型：
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作者：
M. Zahalak;Brenda S. Pratte;Kelly Werth;T. Thiel
钼是许多金属酶（包括硝酸还原酶和钼固氮酶）的辅因子的重要组成部分。蓝藻Anabaena variabilis ATCC 29413使用硝酸盐和大气N2作为生长的氮源。该菌株中的三种固氮酶中有两种是钼依赖性酶，硝酸还原酶也是如此;因此，钼的运输对该菌株的生长很重要。高亲和力转运的黑曲霉素A。variabilis是由modA和modBC产物编码的ABC型转运系统介导的。modBC基因包含融合的orf，其包括对应于大肠杆菌的modB和modC的组分。融合基因的推导出的ModC部分缺乏可识别的结合结构域。通过饥饿诱导modA和modBC的表达。modA或modBC中的突变体不能使用硝酸盐或钼固氮酶生长。在突变体中，使用替代性V-固氮酶的生长没有受损。使用Nif 1 Mo-固氮酶，高浓度的β-内酰胺酶（10 µM）支持modBC突变体的正常生长，表明该菌株中存在低亲和力β-内酰胺酶转运系统。modBC突变体不能检测到运输低浓度的99 Mo（Mo），但运输高浓度。然而，只有在细胞缺乏硫酸盐后才观察到这种转运，这表明诱导型硫酸盐转运系统也可能在该菌株中充当低亲和力的硫酸盐转运系统。
Molybdenum is an essential component of the cofactors of many metalloenzymes including nitrate reductase and Mo‐nitrogenase. The cyanobacterium Anabaena variabilis ATCC 29413 uses nitrate and atmospheric N2 as sources of nitrogen for growth. Two of the three nitrogenases in this strain are Mo‐dependent enzymes, as is nitrate reductase; thus, transport of molybdate is important for growth of this strain. High‐affinity transport of molybdate in A. variabilis was mediated by an ABC‐type transport system encoded by the products of modA and modBC. The modBC gene comprised a fused orf including components corresponding to modB and modC of Escherichia coli. The deduced ModC part of the fused gene lacked a recognizable molybdate‐binding domain. Expression of modA and modBC was induced by starvation for molybdate. Mutants in modA or modBC were unable to grow using nitrate or Mo‐nitrogenase. Growth using the alternative V‐nitrogenase was not impaired in the mutants. A high concentration of molybdate (10 µM) supported normal growth of the modBC mutant using the Nif1 Mo‐nitrogenase, indicating that there was a low‐affinity molybdate transport system in this strain. The modBC mutant did not detectably transport low concentrations of 99Mo (molybdate), but did transport high concentrations. However, such transport was observed only after cells were starved for sulphate, suggesting that an inducible sulphate transport system might also serve as a low‐affinity molybdate transport system in this strain.