Active transport of an antibiotic rifamycin derivative by the outer-membrane protein FhuA
Active transport of an antibiotic rifamycin derivative by the outer-membrane protein FhuA
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DOI：
10.1016/s0969-2126(01)00631-1
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发表时间：
2001-08-01
期刊：
影响因子：
5.7
通讯作者：
Welte, W
中科院分区：
文献类型：
--
作者：
Ferguson, AD;Ködding, J;Welte, W
背景资料：FhuA是大肠杆菌的一种完整膜蛋白，积极转运铁色素和结构相关的抗生素白霉素穿过外膜。这种转运与质子动力相耦合，质子动力通过内膜蛋白TonB为FhuA提供能量。FhuA还运输半合成利福霉素衍生物CGP 4832，虽然这种抗生素的化学结构显着不同，从铁hydroxamates.Results：X-射线晶体学显示，利福霉素CGP 4832占据相同的配体结合位点的铁色素和白霉素，从而表现出令人惊讶的缺乏选择性。然而，利福霉素CGP 4832的结合与FhuA与异羟肟酸盐型配体的复合物不同，因为它不导致开关螺旋的解旋，而仅导致其不稳定，如增加的B因子所反映的。解开的开关螺旋被提出是需要有效的结合TonB的FhuA和耦合的质子动力的细胞质膜与能量依赖性的配体运输。从细胞表达突变体FhuA蛋白的运输数据表明保守的结构和机械的要求，运输这两种类型的compounds.Conclusions：我们得出结论，利福霉素CGP 4832的结合不稳定的开关螺旋，促进形成一个运输主管FhuA-TonB复合物，虽然与铁色素的效率较低。这种利福霉素衍生物的主动转运解释了与利福霉素相比效力增加200倍，利福霉素不是FhuA特异性配体，仅通过被动扩散渗透穿过细胞包膜。
Background: FhuA, an integral membrane protein of Escherichia coli, actively transports ferrichrome and the structurally related antibiotic albomycin across the outer membrane. The transport is coupled to the proton motive force, which energizes FhuA through the inner-membrane protein TonB. FhuA also transports the semisynthetic rifamycin derivative CGP 4832, although the chemical structure of this antibiotic differs markedly from that of ferric hydroxamates.Results: X-ray crystallography revealed that rifamycin CGP 4832 occupies the same ligand binding site as ferrichrome and albomycin, thus demonstrating a surprising lack of selectivity. However, the binding of rifamycin CGP 4832 is deviant from the complexes of FhuA with hydroxamate-type ligands in that it does not result in the unwinding of the switch helix but only in its destabilization, as reflected by increased B factors. Unwinding of the switch helix is proposed to be required for efficient binding of TonB to FhuA and for coupling the proton motive force of the cytoplasmic membrane with energy-dependent ligand transport. The transport data from cells expressing mutant FhuA proteins indicated conserved structural and mechanistic requirements for the transport of both types of compounds.Conclusions: We conclude that the binding of rifamycin CGP 4832 destabilizes the switch helix and promotes the formation of a transport-competent FhuA-TonB complex, albeit with lower efficiency than ferrichrome. Active transport of this rifamycin derivative explains the 200-fold increase in potency as compared to rifamycin, which is not a FhuA-specific ligand and permeates across the cell envelope by passive diffusion only.