Molecular chaperones protect catalase against thermal stress.

Lenticular alpha-crystallin is generally thought of as having limited chaperone functions. It can efficiently suppress the aggregation of proteins but is unable to promote the functional refolding of proteins after denaturation in many systems unlike other molecular chaperones. However, it has been reported that alpha-crystallin, along with the small heat-shock proteins, is able to promote the functional refolding of some enzymes after thermal and chemical denaturation. These chaperones are also able to confer protection against the thermal inactivation of these enzymes. In results presented here, we demonstrate that alpha-crystallin, along with chaperonin 60 (GroEL), was able to provide statistically significant and specific protection against catalase thermal inactivation at stoichiometrical concentrations. The small heat-shock protein, heat-shock protein 25 (Hsp25), was unable to confer any such protection. alpha-Crystallin however was unable to promote the functional refolding of thermally inactivated catalase. alpha-Crystallin and Hsp25 both efficiently suppressed the thermal aggregation of catalase. A high-molecular-mass (HMM) complex was only observed to develop in solutions containing catalase and alpha-crystallin after solutions were 80-fold more concentrated relative to thermal inactivation assay conditions prior to incubation. SDS/PAGE analysis confirmed that alpha-crystallin had formed a soluble complex with catalase after a period of thermal stress.