Tryptophan stabilizes His-heme loops in the denatured state only when it is near a loop end.

ABSTRACT: We use a host-guest approach to evaluate the effect of Trp guest residues relative to Ala on the kinetics and thermodynamics of formation of His-heme loops in the denatured state of iso-1-cytochrome c at 1.5, 3.0, and 6.0 M guanidine hydrochloride (GdnHCl). Trp guest residues are inserted into an alanine-rich segment placed after a unique His near the N-terminus of iso-1-cytochrome c. Trp guest residues are either 4 or 10 residues from the His end of the 28-residue loop. We find the guest Trp stabilizes the His-heme loop at all GdnHCl concentrations when it is the 4th, but not the 10th, residue from the His end of the loop. Thus, residues near loop ends are most important in developing topological constraints in the denatured state that affect protein folding. In 1.5 M GdnHCl, the loop sta

SUBMITTER: Khan MK 

PROVIDER: S-EPMC3341509 | biostudies-literature | 2012 May

REPOSITORIES: biostudies-literature