Effect of Different Crowding Agents (Dextran, PEG and Ficoll) on the Chaperone Ability of β-Casein

Amyloid aggregation is produced from deposition of intermediately folded protein states. Chaperones are assistant molecules that prevent aggregation of protein approximately. In this study we evaluated the effect of different molecular crowding agents (dextran, ficoll and PEG) on chaperoning effect of β-casein in preventing of aggregation of α-lactalbumin. Our results show that dextran and PEG increase the rate of aggregation of α-lactalbumin while ficoll decrease the rate of this aggregation. β-Casein, as a molecular chaperone, prevented aggregation of α-lactalbumin which increased in the presence of ficoll, while its protection activity decreased in the presence of dextran and PEG. The decrease in protection activity of β-casein in the presence of dextran and PEG, is maybe because of enhance in nonspecific interaction between β-casein and α-lactalbumin and environment, or because of the effect of dextran and PEG on the rate of amyloid fibril formation of α-lactalbumin. On the other hand, the increase in chaperone activity of β-casein in the presence of ficoll could be due to the effect of ficoll on the aggregation of target protein and/or reducing the nonspecific interaction between protein and environment. In summary, our data suggest that crowding agents have different effect on the aggregation of α-lactalbumin as well as chaperone activity of β-casein.