Mechanism of Chaperone-like Activity. Suppression of Thermal Aggregation of β_L-Crystallin by α-Crystallin

Abstract

Thermal denaturation and aggregation of beta(L)-crystallin from bovine lens have been studied using differential scanning calorimetry (DSC) and dynamic light scattering (DLS). According to the DLS data, the distribution of the beta(L)-crystallin aggregates by their hydrodynamic radius (R(h)) remains monomodal to the point of precipitating aggregates (sodium phosphate, pH 6.8; 100 mM NaCl; 60 degrees C). The size of the start aggregates (R(h,0)) and duration of the latent stage (t(0)) leading to the formation of the start aggregates have been determined from the light scattering intensity versus the hydrodynamic radius plots and the dependences of R(h) on time. The R(h,0) value remains constant at variation of the beta(L)-crystallin concentration, whereas the t(0) value increases with diminishing beta(L)-crystallin concentration. The suppression of beta(L)-crystallin aggregation by alpha-crystallin is connected with the decrease in the R(h,0) value and increase in the t(0) value. In the presence of alpha-crystallin the aggregate population is split into two components. The first component is represented by stable aggregates whose size remains constant in time. The aggregates of the other kind grow until they reach the size characteristic of aggregates prone to precipitation. The DSC data show that alpha-crystallin has no appreciable influence on thermal denaturation of beta(L)-crystallin.

Kinetics of thermal aggregation of glycogen phosphorylase b from rabbit skeletal muscle: Mechanism of protective action of α‐crystallin

“…For aggregation proceeding in DLCA regime, a universal fractal dimension of 1.8 is observed. As was shown by us earlier, 5,23 the suppression of the rate of thermal aggregation of b L -crystallin and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the presence of a-crystallin, a protein possessing the chaperone-like activity, is due to the transition of the kinetic regime of the aggregation process from the DLCA regime to the regime of reaction-limited cluster-cluster aggregation (RLCA). When the latter regime of aggregation is realized, the sticking probability for the colliding particles is less than unity.…”

“…According to Nicolai and coworkers, [41][42][43][44][45] thermal aggregation of b-lactoglobulin at pH 7 in the presence of 0.1M NaCl proceeds through the stage of the formation of the primary aggregates containing about 100 denatured monomers. In the works by Kurganov and coworkers, 5,23,24,46 these primary aggregates were called the start aggregates to stress the circumstance that the further growth of the primary aggregates occur by their sticking but not by the attachment of the individual molecules of denatured protein. The sticking of the start aggregates and aggregates of higher order results finally in the formation of the large-sized aggregates prone to precipitation.…”

“…21,22 When studying the dependences of the hydrodynamic radius (R h ) of aggregates on time for thermal aggregation of various pro-teins, we showed that these dependences involve the initial linear part followed by a part described by power function. 5,23,24 To describe the initial linear parts of the dependences of R h on time, we used the following equation:…”

“…shown that a-crystallin acting as a molecular chaperone can protect a great variety of proteins from thermal aggregation, [4][5][6][7] and this protein has been found in all tissues, including skeletal muscle. 8 The ability of a-crystallin to suppress heat-induced aggregation of other proteins is reported to be due to hydrophobic interaction with them, 9,10 and it increases when a-crystallin is heated.…”

“…Our previous study reported a new mechanism of protein aggregation, involving the stages of the formation of the start aggregates and further their sticking to aggregates of higher order. 5 a-Crystallin was shown to prevent the aggregation of Phb and reduce the size of formed aggregates. 7 The purpose of the present work was to study the kinetics of thermal aggregation of Phb at a fixed temperature (at 488C) in the presence and absence of a-crystallin using dynamic light scattering (DLS), analytical ultracentrifugation, and measurements of the enzymatic activity, and on the basis of obtained results to propose the molecular mechanism of the protective action of a-crystallin.…”