TonB-dependent receptors—structural perspectives |
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Authors: | Andrew D FergusonJohann Deisenhofer |
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Institution: | a Department of Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9050, USA b Howard Hughes Medical Institute and the University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9050, USA |
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Abstract: | Plants, bacteria, fungi, and yeast utilize organic iron chelators (siderophores) to establish commensal and pathogenic relationships with hosts and to survive as free-living organisms. In Gram-negative bacteria, transport of siderophores into the periplasm is mediated by TonB-dependent receptors. A complex of three membrane-spanning proteins TonB, ExbB and ExbD couples the chemiosmotic potential of the cytoplasmic membrane with siderophore uptake across the outer membrane. The crystallographic structures of two TonB-dependent receptors (FhuA and FepA) have recently been determined. These outer membrane transporters show a novel fold consisting of two domains. A 22-stranded antiparallel β-barrel traverses the outer membrane and adjacent β-strands are connected by extracellular loops and periplasmic turns. Located inside the β-barrel is the plug domain, composed primarily of a mixed four-stranded β-sheet and a series of interspersed α-helices. Siderophore binding induces distinct local and allosteric transitions that establish the structural basis of signal transduction across the outer membrane and suggest a transport mechanism. |
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Keywords: | TonB-dependent receptor Outer membrane protein Siderophore Transporter Signal transduction |
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