The Mechanism of HdeA Unfolding and Chaperone Activation. Issue 1 (5th January 2018)

• Record Type: Journal Article
• Authors: Salmon, Loïc; Stull, Frederick; Sayle, Sabrina; Cato, Claire; Akgül, Şerife; Foit, Linda; Ahlstrom, Logan S.; Eisenmesser, Elan Z.; Al-Hashimi, Hashim M.; Bardwell, James C.A.; Horowitz, Scott
• Is Part Of: Journal of molecular biology. Volume 430:Issue 1(2018)
• Page Start: 33
• Page End: 40
• Publication Date: 2018-01-05
• Subjects: chaperone -- protein folding -- acid -- NMR; MD molecular dynamics -- ITC isothermal titration calorimetry -- MST microscale thermophoresis -- WT wild-type; Molecular biology -- Periodicals; Biology -- Periodicals; Biochemistry -- Periodicals; Bacteriology -- Periodicals; Molecular Biology -- Periodicals; Biochemistry -- Periodicals; Biologie moléculaire -- Périodiques; Biologie -- Périodiques; Biochimie -- Périodiques; Moleculaire biologie; Biochemistry; Biology; Molecular biology; Periodicals; 572.805
• DOI: 10.1016/j.jmb.2017.11.002
• Languages: English
• ISSNs: 0022-2836

Abstract

Abstract: HdeA is a periplasmic chaperone that is rapidly activated upon shifting the pH to acidic conditions. This activation is thought to involve monomerization of HdeA. There is evidence that monomerization and partial unfolding allow the chaperone to bind to proteins denatured by low pH, thereby protecting them from aggregation. We analyzed the acid-induced unfolding of HdeA using NMR spectroscopy and fluorescence measurements, and obtained experimental evidence suggesting a complex mechanism in HdeA's acid-induced unfolding pathway, as previously postulated from molecular dynamics simulations. Counterintuitively, dissociation constant measurements show a stabilization of the HdeA dimer upon exposure to mildly acidic conditions. We provide experimental evidence that protonation of Glu37, a glutamate residue embedded in a hydrophobic pocket of HdeA, is important in controlling HdeA stabilization and thus the acid activation of this chaperone. Our data also reveal a sharp transition from folded dimer to unfolded monomer between pH 3 and pH 2, and suggest the existence of a low-populated, partially folded intermediate that could assist in chaperone activation or function. Overall, this study provides a detailed experimental investigation into the mechanism by which HdeA unfolds and activates. Graphical abstract: Highlights: The acid-stress chaperone HdeA undergoes activation through a complex pathway apparently involving an intermediate state. HdeA is maximally stable at mildly acidic pH.