Solution structure of a peptide model of a region important for the folding of alpha-lactalbumin provides evidence for the formation of nonnative structure in the denatured state.
Elucidating the properties of the denatured state of proteins under conditions relevant for their folding is a key factor in understanding the folding process. We show that a peptide corresponding to residues 111-120 of human alpha-lactalbumin has a pronounced propensity to adopt nonnative structure in aqueous solution. Two-dimensional NMR provides evidence for a structured, nonnative conformation in fast exchange with a random coil ensemble. A total of 78 Rotating Frame Overhauser Effects (ROEs) were used to calculate the conformation of the structured population. A nonnative cluster of hydrophobic residues involving the side chains of K114, W118, Ll119, and A120 is observed, which helps to stabilize a turn-like conformation in the vicinity of residues 115-118. The structure in 30% (vol/vol) TFE was also calculated. Interestingly, the addition of TFE did not simply amplify the population of the structured conformer observed in H2O, but instead induced a new conformation. The implications for the folding of the intact protein are discussed. We also discuss the implications of this study for the relevance of the use of mixed TFE/H2O solvent systems to study isolated peptides.
Demarest
S J
SJ
Department of Chemistry, State University of New York at Stony Brook, 11794-3400, USA.
Raleigh
D P
DP
D002942:Circular Dichroism; D006801:Humans; D007768:Lactalbumin / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding
D007768:Lactalbumin