Chaperone Properties of the Bacterial Periplasmic Substrate-binding Proteins

Abstract

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 substratebinding proteins promote the functional folding of citrate synthase and ␣-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 ␣-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.The periplasmic binding proteins of Gram-negative bacteria constitute a set of at least 30 proteins that are involved in the transport of, and chemotaxis toward, substrates (reviewed in Refs. 1-3). These proteins bind a variety of ligands, such as sugars, amino acids, peptides, ions, and vitamins with submicromolar dissociation constants (1-3). For transport, each periplasmic binding protein interacts with, and delivers its ligand to, a membrane complex comprising one or two integral inner membrane proteins (4 -6) and one or two subunits of an energy-transducing ATPase (7-10). For chemotaxis, each binding protein interacts with an inner membrane receptor that transmits the chemotactic signal to the flagellar apparatus via cytoplasmic components (11,12). For example, the galactosebinding protein MglB of Escherichia coli interacts with the inner membrane chemotransducer Trg, and with a transport complex consisting of the MglC inner membrane protein and the MglA ATPase (13). The polypeptide chain of most binding proteins folds in two globular domains (14). Their specific ligand binds in a cleft between the two globular domains, which are connected by a movable hinge, and upon ligand binding, the two lobes move close to each other and enclose the ligand (15). Interaction of binding proteins with transport and chemotaxis membrane proteins probably involves the rim of the substratebinding cleft, o...

Peptides and ATP binding cassette peptide transporters

“…In this regard, the binding of human plasminogen by the OppAs of the Borellia genus is relevant to note [26]. This observation is consistent with the reports on chaperone activity ascribed to several receptor proteins associated with ABC transporters [47].…”

“…The yield of renatured enzyme in the presence of OppA was comparable with the refolding in the presence of conventional chaperones such as DnaK or DnaJ. Since substrate loading of the receptor did not influence the interaction with unfolded proteins, it is thought that the peptide binding site in OppA Ec is not involved in the chaperone activity [47].…”

Escherichia coli maltose-binding protein as a molecular chaperone for recombinant intracellular cytoplasmic single-chain antibodies 1 1Edited by R. Huber

“…35,69 It has been proposed that the intracellular concentration of these ligand-binding proteins far exceeds what is required for their role in ligand transport and chemotaxis, which may imply that they have additional roles in protein folding and protection from stress in the periplasm. 69 Kapust & Waugh 35 suggested that the ligand-binding cleft of MBP may be involved in its interaction with the fusion partner.…”

“…35,69 It has been proposed that the intracellular concentration of these ligand-binding proteins far exceeds what is required for their role in ligand transport and chemotaxis, which may imply that they have additional roles in protein folding and protection from stress in the periplasm. 69 Kapust & Waugh 35 suggested that the ligand-binding cleft of MBP may be involved in its interaction with the fusion partner. On the other hand, Richrarme et al 69 found that the chaperone activity of periplasmic ligand proteins is unaffected by the presence of ligand, and concluded that the ligand-binding sites of these proteins are not responsible for their chaperone-like activity.…”

Maltose-binding protein switches programmed cell death in Nicotiana glutinosa leaf cells

“…Nowadays, maltose-binding proteins are utilized as one of the best fusion tags to produce soluble recombinant proteins by E. coli system. Most of the expressed proteins are usually able to fold into their biologically active conformations when fused to MBP [20][21][22]. The MBP-fused proteins are often used for the basic investigations including their morpho-molecular interactions with the eukaryotic cells/tissues and several biological assays without the cleavage of their fusion parts [23,24].…”