Influence of Thermal Perturbation of the Oligomeric Size of -Crystallin on its Chaperone Function – A Biophysical Study

Abstract

-Crystallin is the major protein component of the vertebrate eye lens and is composed of two subunits A- and B-, 20 kDa each having 57% sequence homology between them. Both subunits associate to form large oligomer of 800 kDa average molecular weight. It is a key member of the small heat shock protein (sHSP) superfamily having a conserved core ‘-crystallin domain’. -crystallin exhibit molecular chaperone properties and these features play an important role in maintaining the lens transparency. The relationship between oligomerization and chaperone function of -crystallin is less documented in literature. In this thesis, we explored the relationship between oligomeric size and chaperone activity using human recombinant A- and B-crystallin. We used thermal pre-incubation as a tool to vary the oligomeric size of A- and B-crystallin and study its effect on chaperone activity. With increase in pre-incubation temperature, the oligomeric size of both A- and B-crystallin was reduced but the chaperone activity of both proteins was enhanced. This observation leads us to conclude that chaperone activity of -crystallin is inversely proportional to its oligomeric size. Our results also showed that the high molecular weight aggregated species was formed on simple storage of both A- and B-crystallin which has very low chaperone activity. The result implies that loss of chaperone activity of -crystallin can be prevented by preventing its further association into larger oligomer.