title: The small heat-shock protein αB-crystallin uses different mechanisms of chaperone action to prevent the amorphous versus fibrillar aggregation of α-lactalbumin.
abstract: Stress conditions can destabilize proteins, promoting them to unfold and adopt intermediately folded states. Partially folded protein intermediates are unstable and prone to aggregation down off-folding pathways leading to the formation of either amorphous or amyloid fibril aggregates. The sHsp (small heat-shock protein) αB-crystallin acts as a molecular chaperone to prevent both amorphous and fibrillar protein aggregation; however, the precise molecular mechanisms behind its chaperone action are incompletely understood. To investigate whether the chaperone activity of αB-crystallin is dependent upon the form of aggregation (amorphous compared with fibrillar), bovine α-lactalbumin was developed as a model target protein that could be induced to aggregate down either off-folding pathway using comparable buffer conditions. Thus when α-lactalbumin was reduced it aggregated amorphously, whereas a reduced and carboxymethylated form aggregated to form amyloid fibrils. Using this model, αB-crystallin was shown to be a more efficient chaperone against amorphously aggregating α-lactalbumin than when it aggregated to form fibrils. Moreover, αB-crystallin forms high molecular mass complexes with α-lactalbumin to prevent its amorphous aggregation, but prevents fibril formation via weak transient interactions. Thus, the conformational stability of the protein intermediate, which is a precursor to aggregation, plays a critical role in modulating the chaperone mechanism of αB-crystallin.
authors.affiliation: Illawarra Health and Medical Research Institute and School of Biological Sciences, University of Wollongong, NSW 2522, Australia.
authors.forename: Melissa
authors.initials: M
authors.lastname: Kulig
authors.forename: Heath
authors.initials: H
authors.lastname: Ecroyd
mesh_terms: D000818:Animals; D002417:Cattle; D050888:Heat-Shock Proteins, Small / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007768:Lactalbumin / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D038203:alpha-Crystallin B Chain / Q000737:chemistry* / Q000502:physiology*
chemical_list: D050888:Heat-Shock Proteins, Small; D018832:Molecular Chaperones; D038203:alpha-Crystallin B Chain; D007768:Lactalbumin