title: A TonB-like protein and a novel membrane protein containing an ATP-binding cassette function together in exotoxin secretion.
abstract: Protein secretion by many Gram-negative bacteria occurs via the type II pathway involving translocation across the cytoplasmic and outer membranes in separate steps. The mechanism by which metabolic energy is supplied to the translocation across the outer membrane is unknown. Here we show that two Aeromonas hydrophila inner membrane proteins, ExeA and ExeB, are required for this process. ExeB bears sequence as well as topological similarity to TonB, a protein which opens gated ports for the inward translocation of ligands across the outer membrane. ExeA is a novel membrane protein which contains a consensus ATP-binding site. Mutations in this site dramatically decreased the rate of secretion of the toxin aerolysin from the cell. ExeB was stable when overproduced in the presence of ExeA, but was degraded when synthesized in its absence, indicating that the two proteins form a complex. These results suggest that ExeA and ExeB may act together to transduce metabolic energy to the opening of a secretion port in the outer membrane.
authors.affiliation: Department of Biology, University of Regina, Saskatchewan, Canada. peter.howard@uregina.ca
authors.forename: S P
authors.initials: SP
authors.lastname: Howard
authors.forename: H G
authors.initials: HG
authors.lastname: Meiklejohn
authors.forename: D
authors.initials: D
authors.lastname: Shivak
authors.forename: R
authors.initials: R
authors.lastname: Jahagirdar
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D016980:Aeromonas hydrophila / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D001427:Bacterial Toxins / Q000378:metabolism*; D001665:Binding Sites; D001692:Biological Transport; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D016384:Consensus Sequence; D005098:Exotoxins / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D016296:Mutagenesis; D052899:Pore Forming Cytotoxic Proteins; D017386:Sequence Homology, Amino Acid
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D002352:Carrier Proteins; C090402:ExeA protein, Aeromonas hydrophila; C090403:ExeB protein, Aeromonas hydrophila; D005098:Exotoxins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D052899:Pore Forming Cytotoxic Proteins; C057616:tonB protein, Bacteria; C032676:aerolysin; D000255:Adenosine Triphosphate