Publications

• Transport activity of FhuA, FhuC, FhuD, and FhuB derivatives in a system free of polar effects, and stoichiometry of components involved in ferrichrome uptake.

  Mademidis A., Koster W.

  The Escherichia coli fhu operon, composed of the fhuA, C, D, and B genes, is essential for the utilization of ferric siderophores of the hydroxamate type and for the uptake of the antibiotic albomycin. We have had difficulty studying the effects of missense mutations in individual plasmid-encoded ... >> More

  The Escherichia coli fhu operon, composed of the fhuA, C, D, and B genes, is essential for the utilization of ferric siderophores of the hydroxamate type and for the uptake of the antibiotic albomycin. We have had difficulty studying the effects of missense mutations in individual plasmid-encoded transport genes because appropriate test strains were not found: all isolated chromosomal mutations in either one of the fhu genes (with a complete loss of function) negatively influenced the expression of other fhu genes in the operon. In order to analyze Fhu mutant proteins in a system free of polar effects, we constructed a plasmid-encoded gene cassette system by introducing unique restriction sites that allowed precise cloning of individual fhu genes. The fhu cassette operon expressed in a chromosomal fhu deletion mutant enabled us to evaluate the transport activity of mutated FhuA, FhuC, FhuD or FhuB derivatives. In addition, we found that transport across the outer membrane (via FhuA, TonB, ExbB, D) rather than transport across the cytoplasmic membrane (via FhuC, D, B) was rate limiting. The stoichiometry of the components involved in the uptake of iron(III) hydroxamates seems to be important for proper functioning. << Less

  Mol Gen Genet 258:156-165(1998) [PubMed] [EuropePMC]

• Iron(III) hydroxamate transport in Escherichia coli K-12: FhuB-mediated membrane association of the FhuC protein and negative complementation of fhuC mutants.

  Schultz-Hauser G., Koester W., Schwarz H., Braun V.

  Iron(III) hydroxamate transport across the cytoplasmic membrane is catalyzed by the very hydrophobic FhuB protein and the membrane-associated FhuC protein, which contains typical ATP-binding domains. Interaction between the two proteins was demonstrated by immunoelectron microscopy with anti-FhuC ... >> More

  Iron(III) hydroxamate transport across the cytoplasmic membrane is catalyzed by the very hydrophobic FhuB protein and the membrane-associated FhuC protein, which contains typical ATP-binding domains. Interaction between the two proteins was demonstrated by immunoelectron microscopy with anti-FhuC antibodies, which showed FhuB-mediated association of FhuC with the cytoplasmic membrane. In addition, inactive FhuC derivatives carrying single amino acid replacements in the ATP-binding domains suppressed wild-type FhuC transport activity, which arose either from displacement of active FhuC from FhuB by the mutated FhuC derivatives or from the formation of mixed inactive FhuC multimers between wild-type and mutated FhuC proteins. Inactive FhuC derivatives containing internal deletions and insertions showed no phenotypic suppression, indicating conformational alterations that rendered the FhuC derivatives unable to displace wild-type FhuC. It is concluded that the physical interaction between FhuC and FhuB implies a coordinate activity of both proteins in the transport of iron(III) hydroxamates through the cytoplasmic membrane. << Less

  J. Bacteriol. 174:2305-2311(1992) [PubMed] [EuropePMC]

• Point mutations in two conserved glycine residues within the integral membrane protein FhuB affect iron(III) hydroxamate transport.

  Koster W., Bohm B.

  A region of substantial homology, comprising 32 amino acids around a highly conserved glycine residue, is located near the C-terminal ends of the hydrophobic Fhu, Fec, Fep, Fat, and Btu transport proteins involved in the uptake of ferrisiderophores and vitamin B12 into Escherichia coli and Vibrio ... >> More

  A region of substantial homology, comprising 32 amino acids around a highly conserved glycine residue, is located near the C-terminal ends of the hydrophobic Fhu, Fec, Fep, Fat, and Btu transport proteins involved in the uptake of ferrisiderophores and vitamin B12 into Escherichia coli and Vibrio anguillarum. Furthermore, a region similar in location and sequence containing an invariant glycine at an equivalent position was identified in the hydrophobic component of all other periplasmic binding protein-dependent (PBT) systems. In the FhuB protein, which is twice the size of the other PBT-related inner membrane proteins and which displays an internal homology, two conserved glycine residues are present. Alteration of Gly at positions 226 and 559 to Ala, Val, or Glu reduced iron(III) hydroxamate uptake, suggesting that this homologous region may play a general role in the mechanism of PBT-dependent transport. << Less

  Mol Gen Genet 232:399-407(1992) [PubMed] [EuropePMC]