Abstract
This review summarizes experimental data illuminating the mechanism of suppression of heat-induced protein aggregation by α-crystallin, one of the small heat shock proteins. The dynamic light scattering data show that the initial stage of thermal aggregation of proteins is the formation of the initial aggregates involving hundreds of molecules of the denatured protein. Further sticking of the starting aggregates proceeds in a regime of diffusion-limited cluster-cluster aggregation. The protective effect of α-crystallin is due to transition of the aggregation process to the regime of reaction-limited cluster-cluster aggregation, wherein the sticking probability for the colliding particles becomes lower than unity.
Highlights
This review summarizes experimental data illuminating the mechanism of suppression of heat-induced protein aggregation by -crystallin, one of the small heat shock proteins
In the frame of this mechanism of protein aggregation the protective action of -crystallin is due to diminution of the size of the start aggregates and transition of the aggregation process from the diffusion-limited cluster-cluster aggregation (DLCA) regime to the reaction-limited cluster-cluster aggregation (RLCA) regime wherein the sticking probability for the colliding particles becomes lower than unity
One of the functions of molecular chaperones is binding of proteins in unfolded state, which are formed in the course of folding of newly synthesized polypeptide chains or as a result of unfolding of the native proteins under stress conditions
Summary
-Crystallin, the major protein of the mammalian eye lens, is present therein as a polydisperse heterooligomer of A- and B-crystallins, each of a molecular weight of about 20 kDa [1]. The structural changes of -crystallin in response to increased temperature support a possible “activation” step (an irreversible increase in ordered secondary structure, associated with assembly into the high-molecular-mass form) in the chaperone mechanism [6,28] This form of the chaperone associates with partially folded B2crystallin [6] and -lactalbumin [39] intermediates prior to protein aggregation. The efficiency of -crystallin in suppressing fibril formation by -casein and -synuclein increases with temperature This is consistent with an increased chaperone ability of -crystallin at higher temperatures to protect target proteins from amorphous aggregation [35]. In the frame of this mechanism of protein aggregation the protective action of -crystallin is due to diminution of the size of the start aggregates and transition of the aggregation process from the DLCA regime to the reaction-limited cluster-cluster aggregation (RLCA) regime wherein the sticking probability for the colliding particles becomes lower than unity
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