Biochemical Characterization of the Small Heat Shock Protein IbpB from Escherichia coli

作者：Jeffrey R. Shearstone, François Baneyx · 发表于：Journal of Biological Chemistry · 年份：1999 · DOI：10.1074/jbc.274.15.9937 · 被引用次数：104 · 研究领域：Heat shock proteins research、Enzyme Structure and Function、Protein Structure and Dynamics

Escherichia coli IbpB was overexpressed in a strain carrying a deletion in the chromosomal ibp operon and purified by refolding. Under our experimental conditions, IbpB exhibited pronounced size heterogeneity. Basic oligomers, roughly spherical and approximately 15 nm in diameter, interacted to form larger particles in the 100-200-nm range, which themselves associated to yield loose aggregates of micrometer size. IbpB suppressed the thermal aggregation of model proteins in a concentration-dependent manner, and its CD spectrum was consistent with a mostly beta-pleated secondary structure. Incubation at high temperatures led to a partial loss of secondary structure, the progressive exposure of tryptophan residues to the solvent, the dissociation of high molecular mass aggregates into approximately 600-kDa oligomers, and an increase in surface hydrophobicity. Structural changes were reversible between 37 and 55 degrees C, and, up to 55 degrees C, hydrophobic sites were reburied upon cooling. IbpB exhibited a biphasic unfolding trend upon guanidine hydrochloride (GdnHCl) treatment and underwent comparable conformational changes upon melting and during the first GdnHCl-induced transition. However, hydrophobicity decreased with increasing GdnHCl concentrations, suggesting that efficient exposure of structured hydrophobic sites involves denaturant-sensitive structural features. By contrast, IbpB hydrophobicity rose at high NaCl concentrations and increased further at high temperatur...