Dephosphorylation of alpha(s)- and beta-caseins and its effect on chaperone activity: a structural and functional investigation

• Published in: Journal of agricultural and food chemistry 2009-07, Vol.57 (13), p.5956-5964
• Main Authors: Koudelka, Tomas, Hoffmann, Peter, Carver, John A
• Format: Article
• Language: English
• Subjects: Alkaline Phosphatase - metabolism; Caseins - chemistry; Caseins - metabolism; Circular Dichroism; Molecular Chaperones - physiology; Phosphorylation; Protein Folding; Spectrometry, Fluorescence; Static Electricity; Structure-Activity Relationship
• ISSN: 1520-5118
• DOI: 10.1021/jf9008372

Milk casein proteins can act as molecular chaperones: under conditions of stress, such as elevated temperature, molecular chaperones stabilize proteins from unfolding, aggregating, and precipitating. In this study, alpha(s)- and beta-caseins were dephosphorylated using alkaline phosphatase. A structural and functional investigation was undertaken to determine the effect of dephosphorylation on the chaperone activity of alpha(s)- and beta-caseins against two types of protein misfolding, i.e., amorphous aggregation and amyloid fibril assembly. The dephosphorylation of alpha(s)- and beta-caseins resulted in a decrease in the chaperone efficiency against both heat- and reduction-induced amorphously aggregating target proteins. In contrast, dephosphorylation had no effect on the chaperone activity of alpha(s)- and beta-caseins against the amyloid-forming target protein kappa-casein. Circular dichroism and fluorescence spectroscopic data indicated that the loss of negative charge associated with dephosphorylation led to an increase in ordered structure of alpha(s)- and beta-caseins. It is concluded that the flexible, dynamic, and relatively unstructured and amphiphatic nature of alpha(s)- and beta-caseins is important in their chaperone action.