Checking for reversibility of aggregation of UV-irradiated glycogen phosphorylase b under crowding conditions

• UV-irradiated Phb (UV–Phb) is a convenient target protein for the study of the initial stages of aggregation process.
• UV–Phb aggregation induced by crowders at 10 °C can be reversed by dilution or by addition of Arg and Pro.
• At 37 °C Arg induces disintegration of protein aggregates only at early stages of the aggregation process.
• Proposed scheme of aggregation includes the formation of reversible, completely and partly dissociable aggregates.

It is believed that the initial stages of protein aggregation are reversible and can be reversed by simple dilution, whereas prolonged exposure to factors responsible for denaturing proteins (for example, to elevated temperatures) results in the formation of irreversible aggregates. A new approach has been developed to discriminate the stage of the formation of reversible aggregates. Aggregation of UV-irradiated glycogen phosphorylase b (UV–Phb) was studied at 10, 25 and 37 °C in the presence of crowders (polyethylene glycol and Ficoll-70) using dynamic light scattering and analytical ultracentrifugation (pH 6.8; 0.1 M NaCl). The dilution of the protein solution in the course of aggregation at 10 °C results in the breakdown of protein aggregates suggesting that the aggregation process is reversible. When aggregation of UV–Phb is studied at 37 °C, reversibility is lacking. Chemical chaperones (arginine, proline) induce the breakdown of protein aggregates of UV–Phb formed at 10 °C. In the experiments carried out at 37 °C in the presence of crowder the addition of arginine results in disintegration of protein aggregates only at early stages of the aggregation process. It is assumed that general pathway of protein aggregation includes the formation of reversible, completely dissociable, partly dissociable and irreversible aggregates.

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