title: Far-UV circular dichroism reveals a conformational switch in a peptide fragment from the beta-sheet of hen lysozyme.
abstract: The conformation of a 20-residue synthetic peptide corresponding to the antiparallel triple-stranded beta-sheet in hen egg white lysozyme (residues 41-60) has been studied by circular dichroism (CD) and size-exclusion chromatography. In aqueous solution the conformation of the peptide is strongly pH dependent. At pH values below 4.0 and 25 degrees C, the far-UV CD spectrum of the peptide resembles that expected for a predominantly beta-sheet structured (low-pH form), while at pH values exceeding 4.0 the spectrum changes to that of a predominantly unstructured conformation (high-pH form). The far-UV CD spectrum of the high-pH form (pH 6.8) is not affected by changes in the concentration of the peptide and by changes in temperature and ionic strength. By contrast, the far-UV CD spectrum of the low-pH form (pH 2.0) is concentration and temperature dependent but is not affected by ionic strength. Size-exclusion chromatography trimers and higher oligomers and that the monomeric form of the peptide at low pH is predominantly random in nature. Significant helical structure was induced in the high-pH form of the peptide by both trifluoroethanol (TFE) and methanol; by contrast, the conformation of the low-pH form of the peptide was not changed with concentrations of methanol up to 50% (v/v), although in the presence of TFE a state displaying significant helical character was induced. During the transition an intermediate which also displays significant beta-sheet character but which has a distinct CD spectrum is populated. The relevance of this study to the folding pathway of the intact protein is discussed.
authors.affiliation: Oxford Centre for Molecular Sciences, University of Oxford, England.
authors.forename: J J
authors.initials: JJ
authors.lastname: Yang
authors.forename: M
authors.initials: M
authors.lastname: Pikeathly
authors.forename: S E
authors.initials: SE
authors.lastname: Radford
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002645:Chickens; D002850:Chromatography, Gel; D002942:Circular Dichroism; D005260:Female; D006863:Hydrogen-Ion Concentration; D000432:Methanol; D008969:Molecular Sequence Data; D009113:Muramidase / Q000737:chemistry*; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000737:chemistry* / Q000302:isolation & purification; D017433:Protein Structure, Secondary; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature; D014270:Trifluoroethanol
chemical_list: D010446:Peptide Fragments; D014270:Trifluoroethanol; D009113:Muramidase; D000432:Methanol