title: The small heat-shock protein IbpB from Escherichia coli stabilizes stress-denatured proteins for subsequent refolding by a multichaperone network.
abstract: The role of small heat-shock proteins in Escherichia coli is still enigmatic. We show here that the small heat-shock protein IbpB is a molecular chaperone that assists the refolding of denatured proteins in the presence of other chaperones. IbpB oligomers bind and stabilize heat-denatured malate dehydrogenase (MDH) and urea-denatured lactate dehydrogenase and thus prevent the irreversible aggregation of these proteins during stress. While IbpB-stabilized proteins alone do not refold spontaneously, they are specifically delivered to the DnaK/DnaJ/GrpE (KJE) chaperone system where they refold in a strict ATPase-dependent manner. Although GroEL/GroES (LS) chaperonins do not interact directly with IbpB-released proteins, LS accelerate the rate of KJE-mediated refolding of IbpB-released MDH, and to a lesser extent lactate dehydrogenase, by rapidly processing KJE-released early intermediates. Kinetic and gel-filtration analysis showed that denatured MDH preferentially transfers from IbpB to KJE, then from KJE to LS, and then forms a active enzyme. IbpB thus stabilizes aggregation-prone folding intermediates during stress and, as an integral part of a cooperative multichaperone network, is involved in the active refolding of stress-denatured proteins.
authors.affiliation: Department of Plant Sciences, Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel.
authors.forename: L
authors.initials: L
authors.lastname: Veinger
authors.forename: S
authors.initials: S
authors.lastname: Diamant
authors.forename: J
authors.initials: J
authors.lastname: Buchner
authors.forename: P
authors.initials: P
authors.lastname: Goloubinoff
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D018834:Chaperonin 60 / Q000235:genetics; D018833:Chaperonins / Q000378:metabolism*; D002850:Chromatography, Gel; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism*; D007700:Kinetics; D009154:Mutation; D018384:Oxidative Stress; D011489:Protein Denaturation; D017510:Protein Folding
chemical_list: D018834:Chaperonin 60; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; C097579:IbpB protein, E coli; D000255:Adenosine Triphosphate; D018833:Chaperonins