Concentration dependence of chaperone-like activities of α-crystallin, αB-crystallin and proline

Chaperone-like activities of α-crystallin, αB-crystallin and proline were studied using a test system based on aggregation of UV-irradiated glycogen phosphorylase b (Phb) from rabbit skeletal muscle. The biphasic character of the dependence of the initial rate of aggregation (vagg) of UV-irradiated Phb on the concentration of α-crystallin or αB-crystallin is indicative of the existence of two types of chaperone–protein substrate complexes differing significantly in affinity between the components of the complex. The dependence of vagg on the proline concentration is sigmoid (Hill coefficient is equal to 1.6) suggesting that the positive cooperative interactions between the proline molecules bound on the surface of the protein particles occur. When studying the combined suppressive action of α-crystallin and proline on aggregation of UV-irradiated Phb, a slight antagonism between proline used at a fixed concentration (0.15 M) and α-crystallin was observed. At higher concentration of proline (0.5 M) each chaperone acts independent of one another.