title: Escherichia coli small heat shock proteins, IbpA and IbpB, protect enzymes from inactivation by heat and oxidants.
abstract: To examine functions of two small heat shock proteins of Escherichia coli, IbpA and IbpB, we constructed His-IbpA and His-IbpB, in which a polyhistidine tag was fused to the N-terminals. Both purified His-IbpA and His-IbpB formed multimers, which have molecular masses of about 2.0-3.0 MDa and consist of about 100-150 subunits. They suppressed the inactivation of several enzymes including citrate synthase and 6-phosphogluconate dehydrogenase by heat, potassium superoxide, hydrogen peroxide and freeze-thawing, but not the inactivation of glyceraldehyde-3-phosphate dehydrogenase by hydrogen peroxide. Both His-IbpA and His-IbpB suppressed enzyme inactivation by various treatments and were also found to be associated with their non-native forms. However, both His-IbpA and His-IbpB were not able to reactivate enzymes inactivated by heat, oxidants or guanidine hydrochloride. When heated to 50 degrees C, each multimeric form of His-IbpA or His-IbpB was dissociated to form a monomer for His-IbpA, and an oligomer of about one-quarter size for His-IbpB. These structural changes were reversible, as both heated proteins regained the multimeric structures after incubation at 25 degrees C. However, when exposed to hydrogen peroxide or potassium superoxide, the large multimeric forms of His-IbpA and His-IbpB were maintained. The results suggest that His-IbpA and His-IbpB suppress the inactivation of enzymes and bind non-native proteins to protect their structures from heat and oxidants.
authors.affiliation: Department of Biotechnology, Faculty of Engineering, Kansai University, Suita, Osaka, Japan.
authors.forename: Masanobu
authors.initials: M
authors.lastname: Kitagawa
authors.forename: Mizuho
authors.initials: M
authors.lastname: Miyakawa
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Matsumura
authors.forename: Tetsuaki
authors.initials: T
authors.lastname: Tsuchido
mesh_terms: D002950:Citrate (si)-Synthase / Q000037:antagonists & inhibitors; D004789:Enzyme Activation / Q000187:drug effects; D004795:Enzyme Stability / Q000187:drug effects; D004926:Escherichia coli / Q000737:chemistry; D029968:Escherichia coli Proteins; D005954:Glucosephosphate Dehydrogenase / Q000187:drug effects; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D006358:Hot Temperature; D006836:Hydro-Lyases / Q000187:drug effects; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism; D016877:Oxidants / Q000494:pharmacology*; D011108:Polymers
chemical_list: D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; C097578:IbpA protein, E coli; C097579:IbpB protein, E coli; D018832:Molecular Chaperones; D016877:Oxidants; D011108:Polymers; D005954:Glucosephosphate Dehydrogenase; D002950:Citrate (si)-Synthase; D006836:Hydro-Lyases; C022362:phosphogluconate dehydratase