J Biol Chem, Vol. 273, Issue 42, 27236-27244, October 16, 1998
GroEL and GroES Control of Substrate Flux in the in
Vivo Folding Pathway of Phage P22 Coat Protein
Walter S.
Nakonechny and
Carolyn M.
Teschke
From the Department of Molecular and Cell Biology, University of
Connecticut, Storrs, Connecticut 06269-3125
Our present understanding of the action of the
chaperonins GroEL/S on protein folding is based primarily on in
vitro studies, whereas the folding of proteins in the cellular
milieu has not been as thoroughly investigated. We have developed a
means of examining in vivo protein folding and assembly
that utilizes the coat protein of bacteriophage P22, a naturally
occurring substrate of GroEL/S. Here we show that amino acid
substitutions in coat protein that cause a
temperature-sensitive-folding (tsf) phenotype slowed
assembly rates upon increasing the temperature of cell growth. Raising
cellular concentrations of GroEL/S increased the rate of assembly of
the tsf mutant coat proteins to nearly that of wild-type
(WT) coat protein by protecting a thermolabile folding intermediate
from aggregation, thereby increasing the concentration of
assembly-competent coat protein. The rate of release of the tsf coat proteins from the GroEL/S-coat protein ternary
complex was approximately 2-fold slower at non-permissive temperatures when compared with the release of WT coat protein. However, the rate of
release of WT or tsf coat proteins at each temperature remained constant regardless of GroEL/S levels. Thus, raising the
cellular concentration of GroEL/S increased the amount of assembly-competent tsf coat proteins not by altering the
rates of folding but by increasing the probability of GroEL/S-coat
protein complex formation.
Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.