title: The chaperone proteins HSP70, HSP40/DnaJ and GRP78/BiP suppress misfolding and formation of β-sheet-containing aggregates by human amylin: a potential role for defective chaperone biology in Type 2 diabetes.
abstract: Misfolding of the islet β-cell peptide hA (human amylin) into β-sheet-containing oligomers is linked to β-cell apoptosis and the pathogenesis of T2DM (Type 2 diabetes mellitus). In the present study, we have investigated the possible effects on hA misfolding of the chaperones HSP (heat-shock protein) 70, GRP78/BiP (glucose-regulated protein of 78 kDa/immunoglobulin heavy-chain-binding protein) and HSP40/DnaJ. We demonstrate that hA underwent spontaneous time-dependent β-sheet formation and aggregation by thioflavin-T fluorescence in solution, whereas rA (rat amylin) did not. HSP70, GRP78/BiP and HSP40/DnaJ each independently suppressed hA misfolding. Maximal molar protein/hA ratios at which chaperone activity was detected were 1:200 (HSP70, HSP40/DnaJ and GRP78/BiP). By contrast, none of the chaperones modified the secondary structure of rA. hA, but not rA, was co-precipitated independently with HSP70 and GRP78/BiP by anti-amylin antibodies. As these effects occur at molar ratios consistent with chaperone binding to relatively rare misfolded hA species, we conclude that HSP70 and GRP78/BiP can detect and bind misfolded hA oligomers, thereby effectively protecting hA against bulk misfolding and irreversible aggregation. Defective β-cell chaperone biology could contribute to hA misfolding and initiation of apoptosis in T2DM.
authors.affiliation: University of Auckland, New Zealand.
authors.forename: Vita
authors.initials: V
authors.lastname: Chien
authors.forename: Jacqueline F
authors.initials: JF
authors.lastname: Aitken
authors.forename: Shaoping
authors.initials: S
authors.lastname: Zhang
authors.forename: Christina M
authors.initials: CM
authors.lastname: Buchanan
authors.forename: Anthony
authors.initials: A
authors.lastname: Hickey
authors.forename: Thomas
authors.initials: T
authors.lastname: Brittain
authors.forename: Garth J S
authors.initials: GJ
authors.lastname: Cooper
authors.forename: Kerry M
authors.initials: KM
authors.lastname: Loomes
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002942:Circular Dichroism; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism / Q000503:physiopathology; D000091342:Endoplasmic Reticulum Chaperone BiP; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D058228:Islet Amyloid Polypeptide / Q000737:chemistry* / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism / Q000502:physiology; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D051381:Rats; D012996:Solutions
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D058228:Islet Amyloid Polypeptide; D018832:Molecular Chaperones; D012996:Solutions