A change in the pathway of dithiothreitol-induced aggregation of bovine serum albumin in the presence of polyamines and arginine.

When studying the anti-aggregation activity of chemical chaperones, a kinetic regime of the aggregation process for selected test systems should be established. To elucidate the mechanism of suppression of protein aggregation by polyamines (putrescine, spermidine) and arginine, we used a test system based on dithiothreitol (DTT)-induced aggregation of bovine serum albumin (BSA) at 45°C (0.1M Na-phosphate buffer, pH 7.0; [DTT]=2mM). The rate-limiting stage of DTT-induced aggregation of BSA under the studied conditions is that of unfolding of the protein molecule. The kinetics of BSA aggregation was monitored by dynamic light scattering and asymmetric flow field-flow fractionation. On the basis of the obtained data a mechanism of DTT-induced aggregation of BSA in the presence of polyamines and arginine has been proposed. It is assumed that the chemical chaperones under study stabilize the native form of protein with a subsequent decrease in the aggregation rate. However, they stimulate the sticking of aggregates formed in the aggregation process. To prove this mechanism, plots of the hydrodynamic radius of protein aggregates versus the portion of aggregated protein have been constructed.