Molecular modeling of the bacterial outer membrane receptor energizer, ExbBD/TonB, based on homology with the flagellar motor, MotAB.
The MotA/MotB proteins serve as the motor that drives bacterial flagellar rotation in response to the proton motive force (pmf). They have been shown to comprise a transmembrane proton pathway. The ExbB/ExbD/TonB protein complex serves to energize transport of iron siderophores and vitamin B12 across the outer membrane of the Gram-negative bacterial cell using the pmf. These two protein complexes have the same topology and are homologous. Based on molecular data for the MotA/MotB proteins, we propose simple three-dimensional channel structures for both MotA/MotB and ExbB/ExbD/TonB using modeling methods. Features of the derived channels are discussed, and two possible proton transfer pathways for the ExbBD/TonB system are proposed. These analyses provide a guide for molecular studies aimed at elucidating the mechanism by which chemiosmotic energy can be transferred either between two adjacent membranes to energize outer membrane transport or to the bacterial flagellum to generate torque.
Zhai
Yu Feng
YF
Division of Biological Sciences 0116, University of California at San Diego, 9500 Gilam Drive, La Jolla, CA 92093-0116, USA.
Heijne
Wilbert
W
Saier
Milton H
MH
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics; D007473:Ion Channels / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D021381:Protein Transport; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000235:genetics; D016415:Sequence Alignment
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C052874:ExbB protein, E coli; D007473:Ion Channels; D008565:Membrane Proteins; C063010:MotA protein, Bacteria; C064779:MotB protein, Bacteria; D011956:Receptors, Cell Surface; C057616:tonB protein, Bacteria; C489181:tonB protein, E coli; C060790:exbD protein, E coli