Evidence for siderophore-dependent iron acquisition in group B streptococcus
Evidence for siderophore-dependent iron acquisition in group B streptococcus
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DOI：
10.1111/j.1365-2958.2005.04974.x
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发表时间：
2006-01-01
影响因子：
3.6
通讯作者：
Rubens, CE
中科院分区：
文献类型：
--
作者：
Clancy, A;Loar, JW;Rubens, CE
用TnphoZ（一种设计用于鉴定分泌蛋白基因的转座子）诱变B组链球菌（GBS），鉴定出基因同源物fhuD和fhuG。编码的蛋白质参与铁载体（异羟肟酸盐）依赖的铁（III）在其他细菌物种的运输。基因组的序列分析确定fhuD和fhuG是由四个基因fhuCDBG组成的多顺反子操纵子的成员，fhuCDBG分别编码推定的ATP酶、细胞表面受体和两个跨膜蛋白。我们假设FhuD是一种铁载体受体。细胞提取物的Western分析将FhuD定位于细菌细胞膜。荧光猝灭实验确定纯化的FhuD结合异羟肟酸盐型铁载体。FhuD对铁（III）-去铁胺显示出最高的亲和力，K-D（μ M）= 0.05，与金黄色葡萄球菌中FhuD 2的描述相同。Fhu在铁载体-铁运输中的作用也被表征。一个fhu突变体，ACFhu 1，是同样敏感的铁依赖性抗生素链黑菌素的野生型菌株，表明ACFhu 1不减少细胞内铁浓度在没有外源性铁载体。然而，ACFhu 1运输显着减少铁载体结合铁在Fe-55积累试验。这些数据提供了铁载体介导的铁收购GBS的第一个证据。
Mutagenesis of group B streptococcus (GBS) with TnphoZ, a transposon designed to identify secreted protein genes, identified the gene homologues fhuD and fhuG. The encoded proteins participate in siderophore (hydroxamate)-dependent iron(III) transport in other bacterial species. Sequence analysis of the genome determined that fhuD and fhuG are members of a polycistronic operon comprised of four genes, fhuCDBG, that encode a putative ATPase, cell surface receptor and two transmembrane proteins respectively. We hypothesized that FhuD was a siderophore receptor. Western analysis of cell extracts localized FhuD to the bacterial cell membrane. Fluorescence quenching experiments determined that purified FhuD bound hydroxamate-type siderophores. FhuD displayed highest affinity for iron(III)-desferroxamine, with a K-D (mu M) = 0.05, identical to that described for FhuD2 from Staphylococcus aureus. The role of Fhu in siderophore-iron transport was also characterized. A fhu mutant, ACFhu1, was equally sensitive to the iron-dependent antibiotic streptonigrin as the wild-type strain, suggesting that ACFhu1 was not reduced for intracellular iron concentrations in the absence of exogenous siderophore. However, ACFhu1 transported significantly less siderophore-bound iron in Fe-55 accumulation assays. These data provide the first evidence of siderophore-mediated iron acquisition by GBS.