Enterobactin (ENT) is a siderophore (iron-chelating compound) produced by Escherichia coli to gain access to iron, an indispensable nutrient for bacterial growth. ENT is used as an exosiderophore by Pseudomonas aeruginosa with transport of ferri-ENT across the outer membrane by the PfeA transporter. Next to the pfeA gene on the chromosome is localized a gene encoding for an esterase, PfeE, whose transcription is regulated, as for pfeA, by the presence of ENT in bacterial environment. Purified PfeE hydrolyzed ferri-ENT into three molecules of 2,3-DHBS (2,3-dihydroxybenzoylserine) still complexed with ferric iron, and complete dissociation of iron from ENT chelating groups was only possible in the presence of both PfeE and an iron reducer, such as DTT. The crystal structure of PfeE and an inactive PfeE mutant complexed with ferri-ENT or a nonhydrolyzable ferri-catechol complex allowed identification of the enzyme binding site and the catalytic triad. Finally, cell fractionation and fluorescence microscopy showed periplasmic localization of PfeE in P. aeruginosa cells. Thus, the molecular mechanism of iron dissociation from ENT in P. aeruginosa differs from that previously described in E. coli. In P. aeruginosa, siderophore hydrolysis occurs in the periplasm, with ENT never reaching the bacterial cytoplasm. In E. coli, ferri-ENT crosses the inner membrane via the ABC transporter FepBCD and ferri-ENT is hydrolyzed by the esterase Fes only once it is in the cytoplasm.

中文翻译：

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在铜绿假单胞菌中通过铁载体肠杆菌素获得铁的过程中，周质PfeE酯酶的关键作用

肠杆菌素（ENT）是由大肠杆菌产生的铁载体（铁螯合化合物），可用于获取铁（铁是细菌生长必不可少的营养素）。ENT被铜绿假单胞菌用作外鞘膜，而PfeA转运蛋白将Ferri-ENT转运通过外膜。在染色体上pfeA基因的旁边是一个编码酯酶PfeE的基因，该酶的转录受pfeA的调节，是由于细菌环境中存在耳鼻喉科。将PfeE纯化的Ferent-ENT水解成三个仍与三价铁络合的2,3-DHBS（2,3-二羟基苯甲酰基丝氨酸）分子，只有在同时存在PfeE和铁还原剂的情况下，铁才可能从ENT螯合基团上完全解离，例如DTT。PfeE的晶体结构和与亚铁-ENT或不可水解的亚铁-儿茶酚复合物复合的无活性PfeE突变体可以鉴定酶结合位点和催化三联体。最后，细胞分级分离和荧光显微镜检查显示了铜绿假单胞菌细胞中PfeE的周质定位。因此，铜绿假单胞菌中铁从耳鼻喉科解离的分子机制与以前在大肠杆菌中描述的不同。。在铜绿假单胞菌中，铁载体水解发生在周质中，而ENT从未到达细菌的细胞质。在大肠杆菌中， ferri-ENT通过ABC转运蛋白FepBCD穿过内膜，并且只有在其进入细胞质后，酯酶Fes才会水解ferri-ENT。