title: The unusual internal motion of the villin headpiece subdomain.
abstract: The thermostable 36-residue subdomain of the villin headpiece (HP36) is the smallest known cooperatively folding protein. Although the folding and internal dynamics of HP36 and close variants have been extensively studied, there has not been a comprehensive investigation of side-chain motion in this protein. Here, the fast motion of methyl-bearing amino acid side chains is explored over a range of temperatures using site-resolved solution nuclear magnetic resonance deuterium relaxation. The squared generalized order parameters of methyl groups extensively spatially segregate according to motional classes. This has not been observed before in any protein studied using this methodology. The class segregation is preserved from 275 to 305 K. Motions detected in Helix 3 suggest a fast timescale of conformational heterogeneity that has not been previously observed but is consistent with a range of folding and dynamics studies. Finally, a comparison between the order parameters in solution with previous results based on solid-state nuclear magnetic resonance deuterium line shape analysis of HP36 in partially hydrated powders shows a clear disagreement for half of the sites. This result has significant implications for the interpretation of data derived from a variety of approaches that rely on partially hydrated protein samples.
authors.affiliation: Johnson Research Foundation and Department of Biochemistry and Biophysics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, 19104-6059.
authors.forename: Kyle W
authors.initials: KW
authors.lastname: Harpole
authors.affiliation: Johnson Research Foundation and Department of Biochemistry and Biophysics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, 19104-6059.
authors.forename: Evan S
authors.initials: ES
authors.lastname: O'Brien
authors.affiliation: Department of Chemistry, University of Alaska Anchorage, Anchorage, Alaska, 99508.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Clark
authors.affiliation: Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts, 02118.
authors.forename: C James
authors.initials: CJ
authors.lastname: McKnight
authors.affiliation: Department of Chemistry, University of Alaska Anchorage, Anchorage, Alaska, 99508.|Department of Chemistry, University of Colorado at Denver, Denver, Colorado, 80204.
authors.forename: Liliya
authors.initials: L
authors.lastname: Vugmeyster
authors.affiliation: Johnson Research Foundation and Department of Biochemistry and Biophysics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, 19104-6059.
authors.forename: A Joshua
authors.initials: AJ
authors.lastname: Wand
mesh_terms: D000818:Animals; D002645:Chickens; D008840:Microfilament Proteins / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D009038:Motion; D017510:Protein Folding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013696:Temperature
chemical_list: D008840:Microfilament Proteins; C026615:villin
keywords: NMR relaxation; protein dynamics; protein hydration; solid state NMR; solution NMR; temperature dependence; villin headpiece