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AlphaB-crystallin is a member of the sHsp (small heat-shock protein) family that prevents misfolded target proteins from aggregating and precipitating. Phosphorylation at three serine residues (Ser19, Ser45 and Ser59) is a major post-translational modification that occurs to alphaB-crystallin. In the present study, we produced recombinant proteins designed to mimic phosphorylation of alphaB-crystallin by incorporating a negative charge at these sites. We employed these mimics to undertake a mechanistic and structural investigation of the effect of phosphorylation on the chaperone activity of alphaB-crystallin to protect against two types of protein misfolding, i.e. amorphous aggregation and amyloid fibril assembly. We show that mimicking phosphorylation of alphaB-crystallin results in more efficient chaperone activity against both heat-induced and reduction-induced amorphous aggregation of target proteins. Mimick-ing phosphorylation increased the chaperone activity of alphaB-crystallin against one amyloid-forming target protein (kappa-casein), but decreased it against another (ccbeta-Trp peptide). We observed that both target protein identity and solution (buffer) conditions are critical factors in determining the relative chaperone ability of wild-type and phosphorylated alphaB-crystallins. The present study provides evidence for the regulation of the chaperone activity of alphaB-crystallin by phosphorylation and indicates that this may play an important role in alleviating the pathogenic effects associated with protein conformational diseases.

Original publication

DOI

10.1042/BJ20060981

Type

Journal article

Journal

Biochem J

Publication Date

01/01/2007

Volume

401

Pages

129 - 141

Keywords

Animals, Caseins, Catalase, Cattle, Female, Lactalbumin, Liver, Milk, Molecular Chaperones, Nephelometry and Turbidimetry, Phosphorylation, Scattering, Radiation, alpha-Crystallin B Chain