title: Correlations between biological activities and conformational properties for human, salmon, eel, porcine calcitonins and Elcatonin elucidated by CD spectroscopy.
abstract: Calcitonin (CT) inhibits osteoclastic bone resorption and induces calcium uptake from body fluids. A comparative study of the conformational behaviours of therapeutic calcitonins [salmon (s), eel (e), a synthetic eel calcitonin analogue (Elcatonin), porcine (p) and human (h) calcitonins] as a function of solvent polarity and temperature have been performed by circular dichroism spectroscopy. Elements of secondary structure were lacking in H2O but could be observed in 2,2,2-trifluoroethanol and sodium dodecyl sulphate. In particular, similar amounts of alpha-helical content (four alpha-helical turns) were estimated in trifluoroethanol despite the considerable differences in amino acid sequences. The relative ability to form an alpha helix, assessed by trifluoroethanol/H2O titration, was found to be Elcatonin > sCT > pCT > eCT > hCT. In Elcatonin, sCT, pCT and eCT the four alpha-helical turns were promoted almost completely in a single step, between 0 and 35% trifluoroethanol, unlike hCT where helical structure formation has been reported to involve two steps over the whole trifluoroethanol/H2O range [Arvinte, T. & Drake, A. F. (1993) J. Biol. Chem. 268, 6408-6414]. In SDS, which mimics the membrane environment, conformational differences (3-4 helical turns in Elcatonin, sCT, eCT versus one helical turn in pCT, hCT) were observed and correlate well with biological activity (Elcatonin = sCT = eCT > pCT = hCT). Low-temperature studies in a cryogenic solvent mixture showed the formation of high alpha-helix content (similar to that in trifluoroethanol) in Elcatonin, sCT, eCT and pCT, whilst a left-handed extended helix (3(1) helix) was formed in hCT. This is consistent with the hypothesis of 'linear' and 'helical' calcitonin receptors [Nakanuta, H., Orlowski, R. C. & Epand, R. M. (1990) Endocrinology 127, 163-169].
authors.affiliation: Department of Chemistry, Birkbeck College, London, England.
authors.forename: G
authors.initials: G
authors.lastname: Siligardi
authors.forename: B
authors.initials: B
authors.lastname: Samorí
authors.forename: S
authors.initials: S
authors.lastname: Melandri
authors.forename: M
authors.initials: M
authors.lastname: Visconti
authors.forename: A F
authors.initials: AF
authors.lastname: Drake
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002116:Calcitonin / Q000031:analogs & derivatives* / Q000737:chemistry*; D002942:Circular Dichroism; D005260:Female; D006801:Humans; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012756:Sheep; D012967:Sodium Dodecyl Sulfate; D012997:Solvents; D013552:Swine; D013696:Temperature
chemical_list: D012997:Solvents; D012967:Sodium Dodecyl Sulfate; C028815:salmon calcitonin; D002116:Calcitonin; C012755:elcatonin