title: Crystal structure of the dimeric C-terminal domain of TonB reveals a novel fold.
abstract: The TonB-dependent complex of Gram-negative bacteria couples the inner membrane proton motive force to the active transport of iron.siderophore and vitamin B(12) across the outer membrane. The structural basis of that process has not been described so far in full detail. The crystal structure of the C-terminal domain of TonB from Escherichia coli has now been solved by multiwavelength anomalous diffraction and refined at 1.55-A resolution, providing the first evidence that this region of TonB (residues 164-239) dimerizes. Moreover, the structure shows a novel architecture that has no structural homologs among any known proteins. The dimer of the C-terminal domain of TonB is cylinder-shaped with a length of 65 A and a diameter of 25 A. Each monomer contains three beta strands and a single alpha helix. The two monomers are intertwined with each other, and all six beta-strands of the dimer make a large antiparallel beta-sheet. We propose a plausible model of binding of TonB to FhuA and FepA, two TonB-dependent outer-membrane receptors.
authors.affiliation: Macromolecular Crystallography Laboratory, NCI, National Institutes of Health, Frederick, Maryland 21702, USA.
authors.forename: C
authors.initials: C
authors.lastname: Chang
authors.forename: A
authors.initials: A
authors.lastname: Mooser
authors.forename: A
authors.initials: A
authors.lastname: Plückthun
authors.forename: A
authors.initials: A
authors.lastname: Wlodawer
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D019281:Dimerization; D004926:Escherichia coli / Q000737:chemistry; D029968:Escherichia coli Proteins; D008565:Membrane Proteins / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D011994:Recombinant Proteins; C057616:tonB protein, Bacteria; C489181:tonB protein, E coli