THE REACTION CYCLE OF GROEL AND GROES IN CHAPERONIN-ASSISTED PROTEIN-FOLDING

The reaction mechanism of protein folding by the chaperonin GroEL and its regulator GroES has been defined. GroES and substrate protein coun teract each other's effects on GroEL: whereas GroES stabilizes GroEL i n the ADP-bound state, binding of unfolded polypeptide within the cavi ty of the GroEL cylinder triggers ADP and GroES release. Upon ADP-ATP exchange, GroES reassociates with GroEL and ATP hydrolysis discharges the bound protein for folding. Partially folded protein rebinds to the chaperonin, thus perpetuating the cycle until folding is complete.