title: Comparative study of human and salmon calcitonin secondary structure in solutions with low dielectric constants.
abstract: Molecular conformations of salmon (sCT) and human (hCT) calcitonin in media with different concentrations of methanol/water and trifluoroethanol/water have been investigated by fluorescence, circular dichroism (CD) and infrared spectroscopy techniques. In these media, sCT and hCT adopt an alpha-helical structure comprising up to 40-48% of the amino acids. CD experiments reveal that for both peptides, the ordering of the Cys1-Cys7 disulfide link and the alpha-helix formation can be distinguished. Disulfide bond ordering is similar in both calcitonins. sCT adopts the alpha-helical structure more readily than hCT, as solvent polarity is reduced. In 2,2,2-trifluoroethanol (TFE)/water mixtures the alpha-helix formation for both hCT and sCT is a two-step process. The first alpha-helix formation step occurs at lower TFE concentrations (less than 11 mol% TFE for hCT and 6 mol% TFE for sCT). The second alpha-helix formation step represents 50 and 23% of the whole conformational change for hCT and sCT, respectively. Tyrosine fluorescence measurements correlate with the far ultraviolet CD changes associated with the peptide backbone. hCT is seen to adopt a left-handed, extended conformation in aqueous media below -50 degrees C.
authors.affiliation: Ciba-Geigy Pharmaceuticals, Horsham, United Kingdom.
authors.forename: T
authors.initials: T
authors.lastname: Arvinte
authors.forename: A F
authors.initials: AF
authors.lastname: Drake
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002116:Calcitonin / Q000737:chemistry*; D002942:Circular Dichroism; D006801:Humans; D000432:Methanol / Q000737:chemistry; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D012474:Salmon; D012996:Solutions; D012997:Solvents; D013050:Spectrometry, Fluorescence; D014270:Trifluoroethanol / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D012996:Solutions; D012997:Solvents; D014867:Water; D014270:Trifluoroethanol; D002116:Calcitonin; D000432:Methanol