Chaperone properties of the bacterial periplasmic substrate-binding proteins.
Bacterial periplasmic substrate-binding proteins are initial receptors in the process of active transport across cell membranes and/or chemotaxis. Each of them binds a specific substrate (e.g. sugar, amino acid, or ion) with high affinity. For transport, each binding protein interacts with a cognate membrane complex consisting of two hydrophobic proteins and two subunits of a hydrophilic ATPase. For chemotaxis, binding proteins interact with specific membrane chemotaxis receptors. We report, herewith, that the oligopeptide-binding protein OppA of Escherichia coli, the maltose-binding protein MalE of E. coli, and the galactose-binding protein MglB of Salmonella typhimurium interact with unfolded and denatured proteins, such as the molecular chaperones that are involved in protein folding and protein renaturation after stress. These periplasmic substrate-binding proteins promote the functional folding of citrate synthase and alpha-glucosidase after urea denaturation. They prevent the aggregation of citrate synthase under heat shock conditions, and they form stable complexes with several unfolded proteins, such as reduced carboxymethyl alpha-lactalbumin and unfolded bovine pancreatic trypsin inhibitor. These chaperone-like functions are displayed by both the liganded and ligand-free forms of binding proteins, and they occur at binding protein concentrations that are 10-100-fold lower than their periplasmic concentration. These results suggest that bacterial periplasmic substrate-binding proteins, in addition to their function in transport and chemotaxis, might be implicated in protein folding and protection from stress in the periplasm.
Richarme
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Biochimie Génétique, Institut Jacques Monod, Université Paris 7, 75005 Paris, France. richarme@ccr.jussieu.fr
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D018528:ATP-Binding Cassette Transporters; D000818:Animals; D007611:Aprotinin / Q000378:metabolism; D001426:Bacterial Proteins; D001665:Binding Sites; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D002950:Citrate (si)-Synthase / Q000378:metabolism; D029968:Escherichia coli Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D006358:Hot Temperature; D008074:Lipoproteins / Q000378:metabolism; D008297:Male; D058619:Maltose-Binding Proteins; D018832:Molecular Chaperones / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; D011485:Protein Binding; D011489:Protein Denaturation; D017510:Protein Folding; D000520:alpha-Glucosidases / Q000378:metabolism
D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D008074:Lipoproteins; C461619:MalE protein, E coli; D058619:Maltose-Binding Proteins; D018832:Molecular Chaperones; D009004:Monosaccharide Transport Proteins; C499290:OppA protein, E coli; D033902:Periplasmic Binding Proteins; C023550:galactose-binding protein; C461599:maltose transport system, E coli; C499291:oligopeptide-binding protein, Salmonella typhimurium; C046506:oligopeptide-binding protein, bacteria; D007611:Aprotinin; D002950:Citrate (si)-Synthase; D000520:alpha-Glucosidases; C063842:dnaK protein, E coli