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Chaperonin chamber accelerates protein folding through passive action of preventing aggregation

Domenii publicaţii > Chimie + Tipuri publicaţii > Articol în revistã ştiinţificã

Autori: Apetri, Adrian C. and Horwich, Arthur L

Editorial: National Academy of Sciences - USA, PNAS, 2008.


The original experiments reconstituting GroEL–GroES-mediated
protein folding were carried out under ‘‘nonpermissive’’ conditions,
where the chaperonin system was absolutely required and
substrate proteins could not achieve the native state if diluted
directly from denaturant into solution. Under ‘‘permissive’’ conditions,
however, employing lower substrate concentration and
lower temperature, some substrate proteins can be refolded both
by the chaperonin system and while free in solution. For several of
these, the protein refolds more rapidly inside the GroEL–GroES cis
chamber than free in solution, suggesting that the chamber may
have an active role in assisting protein folding. Here, we observe
that the difference is caused by reversible multimolecular association
while folding in solution, an avenue of kinetic partitioning
that slows the overall rate of renaturation relative to the chaperonin
chamber, where such associations cannot occur. For
Rubisco, reversible aggregation during folding in solution was
observed by gel filtration. For a mutant of maltose-binding protein
(DM-MBP), the rate of folding in solution declined with increasing
concentration, and the folding reaction produced light scattering.
Under solution conditions where chloride was absent, however,
light scattering no longer occurred, and DM-MBP folded at the
same rate as in the cis cavity. In a further test, dihydrofolate
reductase, thermally inactivated in the cis cavity or in solution, was
substantially reactivated upon temperature downshift in the cis
cavity but not in solution, where aggregation occurred. We conclude
that the GroEL–GroES chamber behaves as a passive ‘‘Anfinsen
cage’’ whose primary role is to prevent multimolecular association
during folding.

Cuvinte cheie: cis folding, GroEL, maltose-binding protein, Rubisco