l-Arginine induces protein aggregation and transformation of supramolecular structures of the aggregates

Protein misfolding, self-assembly, and aggregation are an essential problem in cell biology, biotechnology, and biomedicine. The protein aggregates are very different morphologically varying from soluble amorphous aggregates to highly ordered amyloid-like fibrils. The objective of this study was to elucidate the role of the amino acid l-arginine (Arg), a widely used suppressor of protein aggregation, in the regulation of transformations of soluble aggregation-prone proteins into supramolecular structures of higher order. However, a striking potential of Arg to govern the initial events in the process of protein aggregation has been revealed under environment conditions where the protein aggregation in its absence was not observed. Using dynamic light scattering we have demonstrated that Arg (10–100 mM) dramatically accelerated the dithiothreitol-induced aggregation of acidic model proteins. The inhibitory effect on the protein aggregation was revealed at higher concentrations of Arg. Using atomic force microscopy it was shown that aggregation of α-lactalbumin from bovine milk induced upon addition of Arg reached a state of formation of supramolecular structures of non-fibrillar species profoundly differing from those of the individual protein in type, size, and shape. The interaction of another positively charged amino acid l-lysine with α-lactalbumin also resulted in profound acceleration of the aggregation process and transformation of supramolecular structures of the aggregates.