Dual effect of arginine on aggregation of phosphorylase kinase

Arginine is widely used in biotechnology as a folding enhancer and aggregation suppressor. However, its action on the stability of complexly organized oligomeric proteins, on the one hand, and its role in the formation of supramolecular structures, on the other hand, are poorly known. The investigation is concerned with the effects of arginine on protein–protein interactions using phosphorylase kinase (PhK) as an example. PhK, a 1.3 MDa (αβγδ)4 hexadecameric complex, is a Ca2+-dependent regulatory enzyme that catalyzes phosphorylation and activation of glycogen phosphorylase b. On the basis of light scattering measurements it was shown that arginine induced aggregation of Ca2+-free PhK. On the contrary, when studying Ca2+, Mg2+-induced aggregation of PhK at 37 °C, the protective effect of arginine was demonstrated. The data on analytical ultracentrifugation are indicative of disruption of PhK hexadecameric structure under the action of arginine. Though HspB6 and HspB5 suppress aggregation of PhK they do not block the disruption effect of arginine with respect to both forms of PhK (Ca2+-free and Ca2+, Mg2+-bound conformers). The dual effect of arginine has been interpreted from view-point of dual behaviour of arginine, functioning both like an osmolyte and a protein denaturant.