Dimerization of TonB is not essential for its binding to the outer membrane siderophore receptor FhuA of Escherichia coli.
FhuA belongs to a family of specific siderophore transport systems located in the outer membrane of Escherichia coli. The energy required for the transport process is provided by the proton motive force of the cytoplasmic membrane and is transmitted to FhuA by the protein TonB. Although the structure of full-length TonB is not known, the structure of the last 77 residues of a fragment composed of the 86 C-terminal amino acids was recently solved and shows an intertwined dimer (Chang, C., Mooser, A., Pluckthun, A., and Wlodawer, A. (2001) J. Biol. Chem. 276, 27535-27540). We analyzed the ability of truncated C-terminal TonB fragments of different lengths (77, 86, 96, 106, 116, and 126 amino acid residues, respectively) to bind to the receptor FhuA. Only the shortest TonB fragment, TonB-77, could not effectively interact with FhuA. We have also observed that the fragments TonB-77 and TonB-86 form homodimers in solution, whereas the longer fragments remain monomeric. TonB fragments that bind to FhuA in vitro also inhibit ferrichrome uptake via FhuA in vivo and protect cells against attack by bacteriophage Phi80.
Koedding
Jiri
J
Fakultaet fuer Biologie, Universitaet Konstanz, Germany.
Howard
Peter
P
Kaufmann
Lindsay
L
Polzer
Patrick
P
Lustig
Ariel
A
Welte
Wolfram
W
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001435:Bacteriophages / Q000737:chemistry; D002455:Cell Division; D003593:Cytoplasm / Q000378:metabolism; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D005291:Ferrichrome / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011522:Protons; D011991:Receptors, Virus / Q000737:chemistry* / Q000378:metabolism; D017262:Siderophores / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000737:chemistry; D014461:Ultracentrifugation
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C050900:FhuA protein, E coli; D008565:Membrane Proteins; D011522:Protons; D011991:Receptors, Virus; D017262:Siderophores; C057616:tonB protein, Bacteria; C489181:tonB protein, E coli; D005291:Ferrichrome; D014364:Tryptophan