TolC is involved in enterobactin efflux across the outer membrane of Escherichia coli
TolC is involved in enterobactin efflux across the outer membrane of Escherichia coli
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DOI：
10.1128/jb.187.19.6701-6707.2005
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发表时间：
2005-10-01
影响因子：
3.2
通讯作者：
Grass, G
中科院分区：
文献类型：
--
作者：
Bleuel, C;Grosse, C;Grass, G
大肠杆菌在缺铁条件下分泌儿茶酚类铁载体肠杆菌素。虽然肠obactin生物合成和铁肠obactin摄取和利用的机制已被广泛了解，但肠obactin如何从细胞输出却几乎一无所知。突变体和高效色谱分析表明，外膜通道通道蛋白TolC，而各自的7种抗性结瘤细胞分裂（RND）蛋白CusA、AcrB、AcrD、AcrF、MdtF （YhiV）或双RND MdtBC （YegNO）都不是肠obactin通过外膜输出所必需的。另外缺失tolC或主要促进剂entS的突变型大肠杆菌菌株在缺铁培养基中生长不足。缺失tolC或entS的菌株，而不缺失RND转运蛋白编码基因的菌株，在生长培养基中分泌的肠杆菌素很少。因此，肠杆菌素在大肠杆菌中的排泄可能是一个两步过程，涉及主要促进剂EntS和外膜通道通道蛋白TolC。基因特异性转录物的定量逆转录pcr分析显示，铁缺失后tolC的表达没有显著变化。然而，缺铁导致RND基因mdtF的表达增加，acrD的表达减少。
Escherichia coli excretes the catecholate siderophore enterobactin in response to iron deprivation. While the mechanisms underlying enterobactin biosynthesis and ferric enterobactin uptake and utilization are widely understood, nearly nothing is known about how enterobactin is exported from the cell. Mutant and high-performance liquid chromatography analyses demonstrated that the outer membrane channel tunnel protein TolC but none of the respective seven resistance nodulation cell division (RND) proteins CusA, AcrB, AcrD, AcrF, MdtF (YhiV), or the twin RND MdtBC (YegNO) was essential for enterobactin export across the outer membrane. Mutant E. coli strains with additional deletion of tolC or the major facilitator entS were growth deficient in iron-depleted medium. Strains with deletion of tolC or entS, but not with deletion of genes encoding RND transporters, excreted very little enterobactin into the growth medium. Enterobactin excretion in E. coli is thus probably a two-step process involving the major facilitator EntS and the outer membrane channel tunnel protein TolC. Quantitative reverse transcription-PCR analysis of gene-specific transcripts showed no significant changes in tolC expression upon iron depletion. However, iron starvation led to increased expression of the RND gene mdtF and a decrease in acrD.