Signal transduction pathway of TonB-dependent transporters

Abstract

Transcription of the ferric citrate import system is regulated by ferric citrate binding to the outer membrane transporter FecA. A signal indicating transporter occupancy is relayed across the outer membrane to energy-transducing and regulatory proteins embedded in the cytoplasmic membrane. Because transcriptional activation is not coupled to ferric citrate import, an allosteric mechanism underlies this complex signaling mechanism. Using evolutionbased statistical analysis we have identified a sparse but structurally connected network of residues that links distant functional sites in FecA. Functional analyses of these positions confirm their involvement in the mechanism that regulates transcriptional activation in response to ferric citrate binding at the cell surface. This mechanism appears to be conserved and provides the structural basis for the allosteric signaling of TonB-dependent transporters.bacterial iron transport ͉ NMR ͉ signaling domain ͉ statistical coupling analysis

Legionella pneumophila LbtU Acts as a Novel, TonB-Independent Receptor for the Legiobactin Siderophore

“…However, the slight differences between the three mutants at the highest CFU concentrations in panel C were not observed in all replicate experiments. minal 22-stranded ␤-barrel that forms a gated porin across the membrane and a long (ϳ150-residue) N-terminal periplasmic domain that acts as a "plug" that opens, with the assistance of TonB-ExbBD, when the receptor is engaged and the siderophore is to be imported (14,28,48,88,92,100,103,117,136). For comparison to LbtU, the secondary structures of two wellknown receptors appear in Fig.…”

Conversion of Cobinamide into Adenosylcobamide in Bacteria and Archaea

“…The BtuB protein is a Ca-dependent transporter located in the outer membrane (9,18,27) that delivers the corrinoid to the periplasmic corrinoid-binding BtuF protein (7,13,60). BtuB function requires energy input, which is provided through interactions with TonB, a protein anchored to the inner membrane whose function is also critical to iron acquisition (22,42). Once bound with the corrinoid, BtuF delivers Cbi to the ABC transporter BtuCD located in the inner membrane (8,20), which translocates it using an ATP-dependent mechanism (Fig.…”

New insights into iron acquisition by cyanobacteria: an essential role for ExbB-ExbD complex in inorganic iron uptake

“…Over the past three decades, many aspects of this TonB-ExbB-ExbD-dependent transport system have been revealed. The crystal structures of several OM transporters and their complexes with TonB are now known (Ferguson et al, 1998(Ferguson et al, , 2002Buchanan et al, 1999;Ferguson and Deisenhofer, 2004;Pawelek et al, 2006;Shultis et al, 2006;Krieg et al, 2009), the signal transduction of OM transporters by interaction with TonB has been elucidated (Ferguson et al, 2007;Kim et al, 2007) and the rotational mechanism of TonB motion has been reported (Jordan et al, 2013). However, with regard to the substrates of the transport system, we are probably only seeing the 'tip of the iceberg' (Schauer et al, 2008).…”