Abstract
Small heat shock proteins (sHsp) with a molecular mass of 15-30 kDa are ubiquitous and conserved. Up to now their function has remained enigmatic. Increased expression under heat shock conditions and their protective effect on cell viability at elevated temperatures suggest that they may have a function in the formation or maintenance of the native conformation of cytosolic proteins. To test this hypothesis we studied the influence of murine Hsp25, human Hsp27, and bovine alpha-B-crystallin (an eye lens protein homologous to sHsps) on the unfolding and refolding of citrate synthase and alpha-glucosidase in vitro. Here we show that all sHsps investigated act as molecular chaperones in these folding reactions. At stoichiometric amounts they maximally prevent the aggregation of citrate synthase and alpha-glucosidase under heat shock conditions and stabilize the proteins. Furthermore, they promote the functional refolding of these proteins after urea denaturation similar to GroE and Hsp90. The interaction both with unfolding and refolding proteins seems to be ATP-independent.
Highlights
Small heat shock proteins with a molecular mass of 15-30 kDa are ubiquitous and conserved
Small heat shock proteins have a molecular mass between Recently, the Hsp9O protein family has been shown to 15and 30 kDa.They exist ahsigh molecular weight complexes belong to the class of molecular chaperones
citrate synthase (CS) and a-glucosidase were used as model systems to study the influence of small heat shock proteins on protein folding and unfolding reactions
Summary
Small heat shock proteins (sHsp) with a molecular mass of 15-30 kDa are ubiquitous and conserved. Renaturation was initiated hy a 100-fold dilution in buffer A. n-Glucosidase was denatured at a concentration of 12.9 p M in 8 M urea, 0.1 M To investigate the functionof sHsps under heat shock conditions we incubated each of the two enzymes at elevated temperatures in the presence or absence of sHsps or a-B-crystallin.
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