1fi1

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Revision as of 12:49, 20 November 2007

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spinqualitylabelsall models 1fi1, resolution 2.90Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

FhuA in complex with lipopolysaccharide and rifamycin CGP4832

Overview

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.

About this Structure

1FI1 is a Single protein structure of sequence from Escherichia coli with PO4, NI, NA, MG, FTT, DPO, RIF and DDQ as ligands. Full crystallographic information is available from OCA.

Reference

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

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