ATP-DEPENDENT CHAPERONING ACTIVITY OF RETICULOCYTE LYSATE

We have developed an assay for chaperone-mediated protein renaturation using thermally denatured Firefly luciferase. Dilution of denatured l uciferase (>99% loss of activity) into reticulocyte lysate typically r esults in recovery of 5-15% activity. Addition of an ATP-regenerating system increases yields to >60%, while heat shock or the addition of d enatured proteins inhibits the chaperoning activity. Reticulocyte lysa te contains abundant quantities of the heat shock proteins, hsp90 and hsp70, and a 60-kDa protein homologous to the yeast stress protein, ST I1. Immune isolated samples of these three proteins support recovery o f up to 35% of luciferase activity in an ATP-dependent manner, suggest ing that these or associated proteins are involved in the renaturation of luciferase. Furthermore, we observed a correlation between lucifer ase renaturation activity and the levels of hsp70 and hsp90 in reticul ocyte lysate preparations. Purified hsp90 and hsp70, along with an ATP -regenerating system, are able to renature luciferase to greater than 20% of its original activity. This renaturation is most efficient when hsp90 and hsp70 are at about a 2:1 ratio and at concentrations simila r to those found in reticulocyte lysate. This study provides evidence for an ATP-dependent chaperoning activity in reticulocyte lysate that involves a cooperative action of hsp70 and hsp90.