ATP-enhanced molecular chaperone functions of the small heat shock protein human αB crystallin

We report direct experimental evidence that human αB-crystallin, a member of the small heat shock protein family, actively participates in the refolding of citrate synthase (CS) in vitro. In the presence of 3.5 mM ATP, CS reactivation by αB-crystallin was enhanced approximately twofold. Similarly, 3.5 mM ATP enhanced the chaperone activity of αB-crystallin on the unfolding and aggregation of CS at 45°C. Consistent with these findings, cell viability at 50°C was improved nearly five orders of magnitude in Escherichia coli expressing αB-crystallin. SDS/PAGE analysis of cell lysates suggested that αB-crystallin protects cells against physiological stress in vivo by maintaining cytosolic proteins in their native and functional conformations. This report confirms the action of αB-crystallin as a molecular chaperone both in vitro and in vivo and describes the enhancement of αB-crystallin chaperone functions by ATP.