Thermal denaturation and aggregation of apoform of glycogen phosphorylase b . Effect of crowding agents and chaperones

The effect of protein and chemical chaperones and crowders on thermal stability and aggregation of apoform of rabbit muscle glycogen phosphorylase b (apoPhb) has been studied at 37°C. Proline suppressed heat‐induced loss in ability of apoPhb to reconstitution at 37°C, whereas α‐crystallin did not reveal a protective action. To compare the antiaggregation activity of intact and crosslinked α‐crystallins, an adsorption capacity (AC) of a protein chaperone with respect to a target protein was estimated. This parameter is a measure of the antiaggregation activity. Crosslinking of α‐crystallin results in 11‐fold decrease in the initial AC. The nonlinear character of the relative initial rate of apoPhb aggregation versus the [intact α‐crystallin]/[apoPhb] ratio plot is indicative of the decrease in the AC of α‐crystallin with increasing the [α‐crystallin]/[apoPhb] ratio and can be interpreted as an evidence for dynamic chaperone structure and polydispersity of α‐crystallin–target protein complexes. As for chemical chaperones, a semisaturation concentration of the latter was used as a characteristic of the antiaggregation activity. A decrease in the semisaturation concentration for proline was observed in the presence of the crowders (polyethylene glycol and Ficoll‐70). © 2013 Wiley Periodicals, Inc. Biopolymers 101: 504–516, 2014.