Studies of αB crystallin subunit dynamics by surface plasmon resonance

The molecular chaperone activity of αB crystallin, an important stress protein in humans, is regulated by physiological factors, including temperature, pH, Ca2+, and ATP. In this study, the role of these factors in regulating the subunit dynamics of human αB crystallin was investigated using surface plasmon resonance (SPR). SPR experiments indicate that at temperatures above 37 °C, where αB crystallin has been reported to have higher chaperone activity, the subunit dynamics of αB crystallin were increased with faster association and dissociation rates. SPR experiments also indicate that interactions between αB crystallin subunits were enhanced with much faster association and slower dissociation rates at pH values below 7.0, where αB crystallin has been reported to have lower chaperone activity. The results suggest that the dynamic and rapid subunit exchange rate may regulate the chaperone activity of αB crystallin. The effect of Ca2+ and ATP on the subunit dynamics of αB crystallin was minimal, suggesting that Ca2+ and ATP modulate the chaperone activity of αB crystallin without altering the subunit dynamics. Based on the SPR results and previously reported biochemical data for the chaperone activity of αB crystallin under different conditions of temperature and pH, a model for the relationship between the subunit dynamics and chaperone activity of αB crystallin is established. The model is consistent with previous biochemical data for the chaperone activity and subunit dynamics of small heat shock proteins (sHSPs) and establishes a working hypothesis for the relationship between complex assembly and chaperone activity for sHSPs.