title: Loop deletions indicate regions important for FhuA transport and receptor functions in Escherichia coli.
abstract: Precise deletions of cell surface-exposed loops of FhuA resulted in mutants of Escherichia coli with distinct phenotypes. Deletion of loop 3 or 11 inactivated ferrichrome transport activity. Deletion of loop 8 inactivated receptor activity for colicin M and the phages T1, T5, and phi80. The loop 7 deletion mutant was colicin M resistant but fully phage sensitive. The loop 4 deletion mutant was resistant to the TonB-dependent phages T1 and phi80 but fully sensitive to the TonB-independent phage T5. The phenotypes of the deletion mutants revealed important sites for the multiple FhuA transport and receptor activities. The ligand binding sites are nonidentical and are distributed among the entire exposed surface. Presumably, FhuA evolved as a ferrichrome transporter and was subsequently used as a receptor by the phages and colicin M, which selected the same as well as distinct loops as receptor sites.
authors.affiliation: Mikrobiologie/Membranphysiologie, Universität Tübingen, Tübingen, Germany.
authors.forename: Franziska
authors.initials: F
authors.lastname: Endriss
authors.forename: Volkmar
authors.initials: V
authors.lastname: Braun
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000502:physiology; D001665:Binding Sites; D001692:Biological Transport; D003087:Colicins / Q000378:metabolism; D003090:Coliphages / Q000254:growth & development; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D005291:Ferrichrome / Q000378:metabolism; D008024:Ligands; D008565:Membrane Proteins / Q000502:physiology; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010641:Phenotype; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011991:Receptors, Virus / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017384:Sequence Deletion
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D003087:Colicins; D029968:Escherichia coli Proteins; C050900:FhuA protein, E coli; D008024:Ligands; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011991:Receptors, Virus; C057616:tonB protein, Bacteria; C489181:tonB protein, E coli; D005291:Ferrichrome