title: Double mutant MBP refolds at same rate in free solution as inside the GroEL/GroES chaperonin chamber when aggregation in free solution is prevented.
abstract: Under "permissive" conditions at 25°C, the chaperonin substrate protein DM-MBP refolds 5-10 times more rapidly in the GroEL/GroES folding chamber than in free solution. This has been suggested to indicate that the chaperonin accelerates polypeptide folding by entropic effects of close confinement. Here, using native-purified DM-MBP, we show that the different rates of refolding are due to reversible aggregation of DM-MBP while folding free in solution, slowing its kinetics of renaturation: the protein exhibited concentration-dependent refolding in solution, with aggregation directly observed by dynamic light scattering. When refolded in chloride-free buffer, however, dynamic light scattering was eliminated, refolding became concentration-independent, and the rate of refolding became the same as that in GroEL/GroES. The GroEL/GroES chamber thus appears to function passively toward DM-MBP.
authors: Howard Hughes Medical Institute, Yale School of Medicine, New Haven, CT 06510, USA.
authors: Navneet K
authors: NK
authors: Tyagi
authors: Wayne A
authors: WA
authors: Fenton
authors: Ashok A
authors: AA
authors: Deniz
authors: Arthur L
authors: AL
authors: Horwich
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