1fi1
FhuA in complex with lipopolysaccharide and rifamycin CGP4832
Structural highlights
FunctionFHUA_ECOLI This receptor binds the ferrichrome-iron ligand. It interacts with the TonB protein, which is responsible for energy coupling of the ferrichrome-promoted iron transport system. Acts as a receptor for bacteriophage T5 as well as T1, phi80 and colicin M. Binding of T5 triggers the opening of a high conductance ion channel. Can also transport the antibiotic albomycin.[1] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedBACKGROUND: 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. Active transport of an antibiotic rifamycin derivative by the outer-membrane protein FhuA.,Ferguson AD, Kodding J, Walker G, Bos C, Coulton JW, Diederichs K, Braun V, Welte W Structure. 2001 Aug;9(8):707-16. PMID:11587645[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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