title: NMR characterization of a peptide model provides evidence for significant structure in the unfolded state of the villin headpiece helical subdomain.
abstract: The villin headpiece subdomain (HP36) is the smallest naturally occurring protein that folds cooperatively. The protein folds on a microsecond time scale. Its small size and very rapid folding have made it a popular target for biophysical studies of protein folding. Temperature-dependent one-dimensional (1D) NMR studies of the full-length protein together with CD and 1D NMR studies of the 21-residue peptide fragment (HP21) derived from HP36 have shown that there is significant structure in the unfolded state of HP36 and have demonstrated that HP21 is a good model of these interactions. Here, we characterized the model peptide HP21 in detail by two-dimensional NMR. Strongly upfield shifted C(alpha) protons, the magnitude of the 3J(NH,alpha) coupling constants, and the pattern of backbone-backbone and backbone-side chain NOEs indicate that the ensemble of structures populated by HP21 contains alpha-helical structure and native as well as non-native hydrophobic contacts. The hydrogen-bonded secondary structure inferred from the NOEs is, however, not sufficient to confer significant protection against amide H-D exchange. These studies indicate that there is significant secondary structure and hydrophobic clustering in the unfolded state of HP36. The implications for the folding of HP36 are discussed.
authors.affiliation: Department of Chemistry, State University of New York, Stony Brook, New York 11790-3400, USA.
authors.forename: Yuefeng
authors.initials: Y
authors.lastname: Tang
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Goger
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Raleigh
mesh_terms: D000595:Amino Acid Sequence; D029721:Drosophila Proteins / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008840:Microfilament Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D016900:Neurofilament Proteins / Q000737:chemistry; D010446:Peptide Fragments / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D029721:Drosophila Proteins; C512164:HP21 peptide; D008840:Microfilament Proteins; D016900:Neurofilament Proteins; D010446:Peptide Fragments; C026615:villin; C115223:villin headpiece subdomain peptide