E. Lopezhernandez et al., FOLDING KINETICS OF CHE-Y MUTANTS WITH ENHANCED NATIVE ALPHA-HELIX PROPENSITIES, Journal of Molecular Biology, 266(3), 1997, pp. 610-620
in this work we study the folding kinetics of Che Y mutants in which t
he helical propensity of each of its five alpha-helices has been great
ly enhanced by local interactions (between residues close in sequence)
. This constitutes an experimental test on the role of local interacti
ons in protein folding, as well as providing new information on the de
tails of the folding pathway of the protein Che Y. With respect to the
first issue, our results show that the enhancement of helical propens
ities by native-like local interactions in Che Y has the following gen
eral effects: (1) the energetics of the whole Che Y folding energy lan
dscape (folded state, intermediate, denatured state and main transitio
n state) are affected by the enhancement of helical propensities, thus
, native-like local interactions appear to have a low specificity for
the native conformation; (2) our results support the idea, proposed fr
om thermodynamic analysis of the mutants, that the denatured state und
er native conditions becomes more compact upon enhancement of helical
propensities; (3) the rate of folding in aqueous solution decreases in
all the mutants, suggesting that the optimization of the folding rate
in this protein requires low secondary structure propensities. Regard
ing the description of the folding pathway of Che Y, we find evidence
that the folding transition state of Che Y is constituted by two sub-d
omains with different degree of helical structure. The first includes
helices 1 and 2 which are rather structured, while the second encompas
ses the last three helices, which are very unstructured. On the other
hand, the same analysis for the folding intermediate indicates that al
l the five alpha-helices are, on average, rather structured. Thus, sug
gesting that a large structural reorganization of the last three alpha
-helices must take place before folding can be completed. This conclus
ion indicates that the folding intermediate of Che Y is a misfolded sp
ecies. (C) 1997 Academic Press Limited.