title: The role of PII conformations in the calculation of peptide fractional helix content.
abstract: Changes in the temperature, pH, ionic strength, or denaturant concentration of aqueous solutions of the monomeric non-alpha-helical peptide acetylYEAAAKEAPAKEAAAKAamide generate changes in its dichroic spectrum characteristic for a conformational transition. This transition has the characteristic features of a residue PII/unstructured conformational equilibrium in which PII denotes an extended left-handed helical conformation and unstructured denotes all the remaining conformations in a random coil ensemble. Replacement of the proline residue facilitates population of residues in an alpha-helical conformation. However, the ellipticity values for these non-proline peptides merge with the ellipticity of the proline peptide as the population of residues in the alpha-helix conformation is diminished. This convergence suggests that all residues in a host/guest peptide series of the same length share a common PII/unstructured conformational equilibrium in a given solvent. We propose that the fractional helix content of peptides within such a series may be estimated by using a two-state calculation in which the ellipticity for the non-alpha-helix conformations is provided by a peptide having a central proline guest residue.
authors.affiliation: Department of Biochemistry, University of Iowa, Iowa City 52242, USA.
authors.forename: S H
authors.initials: SH
authors.lastname: Park
authors.forename: W
authors.initials: W
authors.lastname: Shalongo
authors.forename: E
authors.initials: E
authors.lastname: Stellwagen
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation; D012997:Solvents; D013696:Temperature
chemical_list: D010455:Peptides; D012997:Solvents