Chaperonins cpn60/cpn10 (GroEL/GroES in Escherichia
coli) assist folding of nonnative polypeptides. Folding
of the chaperonins themselves is distinct in that it entails
assembly of a sevenfold symmetrical structure. We have
characterized denaturation and renaturation of the recombinant
human chaperonin 10 (cpn10), which forms a heptamer. Denaturation
induced by chemical denaturants urea and guanidine hydrochloride
(GuHCl) as well as by heat was monitored by tyrosine fluorescence,
far-ultraviolet circular dichroism, and cross-linking;
all denaturation reactions were reversible. GuHCl-induced
denaturation was found to be cpn10 concentration dependent,
in accord with a native heptamer to denatured monomer transition.
In contrast, urea-induced denaturation was not cpn10 concentration
dependent, suggesting that under these conditions cpn10
heptamers denature without dissociation. There were no
indications of equilibrium intermediates, such as folded
monomers, in either denaturant. The different cpn10 denatured
states observed in high [GuHCl] and high [urea]
were supported by cross-linking experiments. Thermal denaturation
revealed that monomer and heptamer reactions display the
same enthalpy change (per monomer), whereas the entropy-increase
is significantly larger for the heptamer. A thermodynamic
cycle for oligomeric cpn10, combining chemical denaturation
with the dissociation constant in absence of denaturant,
shows that dissociated monomers are only marginally stable
(3 kJ/mol). The thermodynamics for co-chaperonin stability
appears conserved; therefore, instability of the monomer
could be necessary to specify the native heptameric structure.