title: The Escherichia coli small heat-shock proteins IbpA and IbpB prevent the aggregation of endogenous proteins denatured in vivo during extreme heat shock.
abstract: The roles of the Escherichia coli IbpA and IbpB chaperones in protection of heat-denatured proteins against irreversible aggregation in vivo were investigated. Overproduction of IbpA and IbpB resulted in stabilization of the denatured and reversibly aggregated proteins (the S fraction), which could be isolated from E. coli cells by sucrose gradient centrifugation. This finding is in agreement with the present model of the small heat-shock proteins' function, based mainly on in vitro studies. Deletion of the ibpAB operon resulted in almost twofold increase in protein aggregation and in inactivation of an enzyme (fructose-1,6-biphosphate aldolase) in cells incubated at 50 degrees C for 4 h, decreased efficiency of the removal of protein aggregates formed during prolonged incubation at 50 degrees C and affected cell viability at this temperature. IbpA/B proteins were not needed for removal of protein aggregates or for the enzyme protection/renaturation in cells heat shocked at 50 degrees C for 15 min. These results show that the IbpA/B proteins are required upon an extreme, long-term heat shock. Overproduction of IbpA but not IbpB caused an increase of the level of beta-lactamase precursor, which was localized in the S fraction, together with the IbpA protein, which suggests that the unfolded precursor binds to IbpA but not to IbpB. Although in the wild-type cells both E. coli small heat-shock proteins are known to localize in the S fraction, only 2% of total IbpB co-localized with the aggregated proteins in the absence of IbpA, while in the absence of IbpB, the majority of IbpA was present in the aggregates fraction.
authors.affiliation: Department of Biochemistry, University of Gdańsk, Kładki 24, 80-822 Gdańsk, Poland1.
authors.forename: Dorota
authors.initials: D
authors.lastname: Kuczynska-Wisnik
authors.affiliation: Department of Biochemistry, University of Gdańsk, Kładki 24, 80-822 Gdańsk, Poland1.
authors.forename: Sabina
authors.initials: S
authors.lastname: Kçdzierska
authors.affiliation: Department of Biochemistry, University of Gdańsk, Kładki 24, 80-822 Gdańsk, Poland1.
authors.forename: Ewelina
authors.initials: E
authors.lastname: Matuszewska
authors.affiliation: School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK2.
authors.forename: Peter
authors.initials: P
authors.lastname: Lund
authors.affiliation: Department of Molecular Biology, University of Gdańsk, Kładki 24, 80-822 Gdańsk, Poland3.
authors.forename: Alina
authors.initials: A
authors.lastname: Taylor
authors.affiliation: Department of Biochemistry, University of Gdańsk, Kładki 24, 80-822 Gdańsk, Poland1.
authors.forename: Barbara
authors.initials: B
authors.lastname: Lipinska
authors.affiliation: Department of Biochemistry, University of Gdańsk, Kładki 24, 80-822 Gdańsk, Poland1.
authors.forename: Ewa
authors.initials: E
authors.lastname: Laskowska
mesh_terms: D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism*; D017353:Gene Deletion; D015870:Gene Expression; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D018869:Heat-Shock Response / Q000235:genetics / Q000502:physiology*; D008957:Models, Genetic; D018832:Molecular Chaperones / Q000378:metabolism; D009876:Operon / Q000235:genetics; D011489:Protein Denaturation; D001618:beta-Lactamases / Q000737:chemistry / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C097578:IbpA protein, E coli; C097579:IbpB protein, E coli; D018832:Molecular Chaperones; D001618:beta-Lactamases; C063842:dnaK protein, E coli