title: TonB or not TonB: is that the question?
abstract: Bacteria are able to survive in low-iron environments by sequestering this metal ion from iron-containing proteins and other biomolecules such as transferrin, lactoferrin, heme, hemoglobin, or other heme-containing proteins. In addition, many bacteria secrete specific low molecular weight iron chelators termed siderophores. These iron sources are transported into the Gram-negative bacterial cell through an outer membrane receptor, a periplasmic binding protein (PBP), and an inner membrane ATP-binding cassette (ABC) transporter. In different strains the outer membrane receptors can bind and transport ferric siderophores, heme, or Fe3+ as well as vitamin B12, nickel complexes, and carbohydrates. The energy that is required for the active transport of these substrates through the outer membrane receptor is provided by the TonB/ExbB/ExbD complex, which is located in the cytoplasmic membrane. In this minireview, we will briefly examine the three-dimensional structure of TonB and the current models for the mechanism of TonB-dependent energy transduction. Additionally, the role of TonB in colicin transport will be discussed.
authors: Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
authors: Karla D
authors: KD
authors: Krewulak
authors: Hans J
authors: HJ
authors: Vogel
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000166:cytology / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D003087:Colicins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007501:Iron / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017262:Siderophores / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D003087:Colicins; D008565:Membrane Proteins; D017262:Siderophores; C057616:tonB protein, Bacteria; D007501:Iron