The beta-barrel domain of FhuADelta5-160 is sufficient for TonB-dependent FhuA activities of Escherichia coli.

Abstract

FhuA in the outer membrane of Escherichia coli serves as a transporter for ferrichrome, the antibiotics albomycin and rifamycin CGP4832, colicin M, and as receptor for phages T1, T5 and phi80. The previously determined crystal structure reveals that residues 160-714 of the mature protein form a beta-barrel that is closed from the periplasmic side by the globular N-proximal fragment, residues 1-159, designated the cork. In this study, deletion of the cork resulted in a stable protein, FhuADelta5-160, that was incorporated in the outer membrane. Cells that synthesized FhuADelta5-160 displayed a higher sensitivity to large antibiotics such as erythromycin, rifamycin, bacitracin and vancomycin, and grew on maltotetraose and maltopentaose in the absence of LamB. Higher concentrations of ferrichrome supported growth of a tonB mutant that synthesized FhuADelta5-160. These results demonstrate non-specific diffusion of compounds across the outer membrane of cells that synthesize FhuADelta5-160. However, growth of a FhuADelta5-160 tonB wild-type strain occurred at low ferrichrome concentrations, and ferrichrome was transported at about 45% of the FhuA wild-type rate despite the lack of ferrichrome binding sites provided by the cork. FhuADelta5-160 conferred sensitivity to the phages and colicin M at levels similar to that of wild-type FhuA, and to albomycin and rifamycin CGP 4832. The activity of FhuADelta5-160 depended on TonB, although the mutant lacks the TonB box (residues 7-11) previously implicated in the interaction of FhuA with TonB. CCCP inhibited tonB-dependent transport of ferrichrome through FhuADelta5-160. FhuADelta5-160 still functions as a specific transporter, and sites in addition to the TonB box are involved in the TonB-mediated response of FhuA to the proton gradient of the cytoplasmic membrane. It is proposed that TonB interacts with the TonB box of FhuA and with the beta-barrel to release ferrichrome from the FhuA binding sites and to open the channel in FhuA. For transport of ferrichrome through the open channel of FhuADelta5-160, interaction of TonB with the beta-barrel is sufficient to release ferrichrome from the residual binding sites at the beta-barrel and to induce the active conformation of the L4 loop at the cell surface for infection by the TonB-dependent phages T1 and phi80.

• Authors: M Braun, H Killmann, V Braun
• Journal: Molecular microbiology (Mol Microbiol) Vol. 33 Issue 5 Pg. 1037-49 (Sep 1999) ISSN: 0950-382X [Print] England
• PMID: 10476037 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Anti-Bacterial Agents
• Bacterial Outer Membrane Proteins
• Bacterial Proteins
• Bacteriocins
• Colicins
• Escherichia coli Proteins
• FhuA protein, E coli
• Membrane Proteins
• Receptors, Virus
• Rifamycins
• tonB protein, Bacteria
• tonB protein, E coli
• CGP 4832
• microcin
• Ferrichrome
• albomycin

Topics

• Anti-Bacterial Agents (pharmacology)
• Bacterial Outer Membrane Proteins (chemistry, genetics, metabolism)
• Bacterial Proteins (metabolism)
• Bacteriocins (pharmacology)
• Biological Transport
• Colicins (pharmacology)
• Coliphages (pathogenicity)
• Escherichia coli (drug effects, metabolism, virology)
• Escherichia coli Proteins
• Ferrichrome (analogs & derivatives, metabolism, pharmacology)
• Membrane Proteins (metabolism)
• Mutation
• Protein Conformation
• Receptors, Virus (chemistry, genetics, metabolism)
• Rifamycins (pharmacology)
• Sequence Deletion