This is a short domain found at the N-terminus of the Secretins of the bacterial type II/III secretory system as well as the TonB-dependent receptor proteins. These proteins are involved in TonB-dependent active uptake of selective substrates.
This is a conserved region found at the N-terminal region of bacterial proteins involved in either protein secretion or the uptake of selective substrates, including:
Bundle-forming pilus protein B, an outer-membrane protein absolutely required for pilus biogenesis, and for enteropathogenic Escherichia coli localized adherence and autoaggregation [(PUBMED:8932312)].
PilQ, which is required for type IV pilus biogenesis and competence and is thought to function both as a pore for exit of the pilus and as a channel for entry of haem and antimicrobial agents and uptake of transforming DNA [(PUBMED:14729699)].
PupB, a specific receptor for the siderophores ferric pseudobactin BN8 and ferric pseudobactin BN7, iron chelating molecules that allow the organism to extract iron from the environment, especially under iron-restricted conditions [(PUBMED:8392140)].
TonB, which couples the electrochemical potential of the cytoplasmic membrane to the active transport of iron-siderophores and vitamin B12 across the outer membrane [(PUBMED:15802653)].
Deletion of the proline-rich region of TonB disrupts formation of a 2:1complex with FhuA, an outer membrane receptor of Escherichia coli.
Protein Sci. 2005; 14: 1266-73
Display abstract
TonB protein of Escherichia coli couples the electrochemical potential ofthe cytoplasmic membrane (CM) to active transport of iron-siderophores andvitamin B(12) across the outer membrane (OM). TonB interacts with OMreceptors and transduces conformationally stored energy. Energy fortransport is provided by the proton motive force through ExbB and ExbD,which form a ternary complex with TonB in the CM. TonB contains threedistinct domains: an N-terminal signal/anchor sequence, a C-terminaldomain, and a proline-rich region. The proline-rich region was proposed toextend TonB's structure across the periplasm, allowing it to contactspatially distant OM receptors. Having previously identified a 2:1stoichiometry for the complex of full-length (FL) TonB and the OM receptorFhuA, we now demonstrate that deletion of the proline-rich region of TonB(TonBDelta66-100) prevents formation of the 2:1 complex. Sedimentationvelocity analytical ultracentrifugation of TonBDelta66-100 with FhuArevealed that a 1:1 TonB-FhuA complex is formed. Interactions betweenTonBDelta66-100 and FhuA were assessed by surface plasmon resonance, andtheir affinities were determined to be similar to those of TonB (FL)-FhuA.Presence of the FhuA-specific siderophore ferricrocin altered neitherstoichiometry nor affinity of interaction, leading to our conclusion thatthe proline-rich region in TonB is important in forming a 2:1high-affinity TonB-FhuA complex in vitro. Furthermore,TonBDelta66-100-FhuADelta21-128 interactions demonstrated that the corkregion of the OM receptor was also important in forming a complex.Together, these results demonstrate a novel function of the proline-richregion of TonB in mediating TonB-TonB interactions within the TonB-FhuAcomplex.
BfpB, an outer membrane lipoprotein required for the biogenesis ofbundle-forming pili in enteropathogenic Escherichia coli.
J Bacteriol. 1996; 178: 6555-63
Display abstract
The bundle-forming pili (BFP) of enteropathogenic Escherichia coli arebelieved to play a role in pathogenesis by causing the formation ofbacterial microcolonies that bind epithelial surfaces of the smallintestine. This in vivo process is mimicked in vitro by theautoaggregation and localized adherence phenotypes. Expression of BFP, amember of the type IV pilus family, requires the enteroadherence factor(EAF) plasmid, which contains bfpA, the gene that encodes the principalstructural subunit of BFP. Immediately downstream of bfpA are 13 openreading frames transcribed in the same direction as bfpA; together withbfpA, these compose the bfp gene cluster. Disruption of bfpB, the secondopen reading frame downstream of bfpA, was performed by allelic exchange.The resulting mutant, B171-8deltaB, did not exhibit the autoaggregation orlocalized adherence phenotype or produce BFP filaments. Thus, BfpB isrequired for pilus biogenesis. However, BfpA was produced at wild-typelevels and processed normally by B171-8deltaB, indicating that BfpB actsat a step in the BFP biogenic pathway after production and processing ofthe structural subunit. Biochemical and cell fractionation studies showedthat BfpB is a 58-kDa lipoprotein that is located primarily in the outermembrane. Assays of bfpA and bfpB mRNAs and protein expression showed thatboth genes are cotranscribed as part of an environmentally responsiveoperon that is regulated by growth phase and ammonium.
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