28
Aggregation, Protein
transient association of intermediates has
been obtained from small angle X-ray
scattering, in the case of apomyoglobin
by Doniach and his group, and in the
case of carbonic anhydrase by Semisot-
nov and Kuwajima, and by Silow et al.
During the refolding of phosphoglycer-
ate kinase, rapidly transient multimeric
species (dimers, trimers, and tetramers)
yielding to the native monomeric protein
have been detected by Pecorari et al. These
species are not in equilibrium, but are
formed rapidly and disappear in the slow
folding step. Unlike classical aggregates,
their distribution does not depend on pro-
tein concentration, and they are produced
at concentrations as low as 0
.
05
µ
M. The
distribution of the oligomers is completely
established at the end of the fast refolding
step. To take into account all these obser-
vations, a model, which is formally similar
to a reaction of copolymerization between
two types of monomers, has been pro-
posed. In this model, the refolding of the
protein produces two types of intermedi-
ate conformers that can associate with the
same or the other type. In the latter case,
the association cannot be extended further
(Fig. 2). Transient multimeric species have
also been observed during the refolding
of the isolated N-terminal domain under
conditions in which neither the whole
native protein nor the folded isolated N-
domain associate. However, they cannot
transform to the native form in the absence
of the interactions with the complementary
Denatured protein
Folded
protein
k
1
k
2
Fast phase
Slow phase
Fig. 2
Model proposed for the formation of
transient multimeric species during the refolding
of yeast phosphoglycerate kinase. Two types of
conformers are produced in the early step of
folding. One of these can be directionally
extended by association with either the same
conformer or another type of conformer. In this
last case, the association cannot be further
extended. The distribution of species results
from a kinetic competition between two kinetic
processes. (Reproduced from Pecorari, F.,
Minard, P., Desmadril, M.,Yon, J.M. (1996)
Occurrence of transient multimeric species
during the refolding of a monomeric protein,
J.
Biol. Chem.
271
, 5270–5276.)
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