Send to

Choose Destination
J Mol Biol. 1996 Oct 25;263(2):311-22.

Microsecond protein folding through a compact transition state.

Author information

Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA.


Dynamic NMR methods have been employed to measure the folding and unfolding rate constants of two extremely fast-folding proteins. lambda 6-85, a truncated, monomeric form of the N-terminal domain of lambda repressor, refolds with a lifetime of approximately 250 microseconds. These methods have also been applied to a thermostable lambda 6-85 variant with alanine substituted for glycine residues 46 and 48 in the third helix (G46A/G48A). Both proteins exhibit linear ln (kf,u) versus [urea] plots, consistent with two-state folding for both proteins. When extrapolated to 0M urea, the data indicate that G46A/G48A folds with a lifetime of less than 20 microseconds. The slopes of the ln (kf,u) versus [urea] curves (mu and mf) indicate that the modest Gly-->Ala double mutation dramatically changes the transition state solvent accessibility. The transition state for lambda 6-85 has a fractional accessibility (mu/(mu-mf)) of 0.61, whereas the transition state for G46A/G48A is much more native-like, with a fractional accessibility of 0.16. The extraordinary change in the folding pathway that these mutations induce suggests that the intrinsic stability of helix 3 is an important determinant of the folding mechanism.

[Indexed for MEDLINE]

Supplemental Content

Full text links

Icon for Elsevier Science
Loading ...
Support Center