title: Using D-Amino Acids to Delineate the Mechanism of Protein Folding: Application to Trp-cage.
abstract: Using the miniprotein Trp-cage as a model, we show that D-amino acids can be used to facilitate the delineation of protein folding mechanism. Specifically, we study the folding-unfolding kinetics of three Trp-cage mutants where the native glycine residue near the C-terminus of the α-helix is replaced by a D-amino acid. A previous study showed that these mutations increase the Trp-cage stability, due to a terminal capping effect. Our results show that the stabilizing effect of D-asparagine and D-glutamine originates almost exclusively from a decrease in the unfolding rate, while the D-alanine mutation results in a similar decrease in the unfolding rate, but it also increases the folding rate. Together, these results support a folding mechanism wherein the α-helix formation in the transition state is nucleated at the N-terminus, whereas those long-range native interactions stabilizing this helix are developed at the downhill side of the folding free energy barrier.
authors.affiliation: Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Culik
authors.forename: Srinivas
authors.initials: S
authors.lastname: Annavarapu
authors.forename: Vikas
authors.initials: V
authors.lastname: Nanda
authors.forename: Feng
authors.initials: F
authors.lastname: Gai