Conformational analysis of the melanin-concentrating hormone core by circular dichroic spectroscopy. Disulphide bridge and tyrosine contributions.
A detailed circular dichroic (CD) study of the conformational flexibility of the melanin-concentrating hormone core [MCH(5-14)] is reported. Variable pH (2-10) and temperature (-80 degrees to +80 degrees C) in aqueous media reveal that CD contributions from tyrosine, disulphide bridge and the amide backbone can be discriminated. Only below -10 degrees C does a preferred -S-S-conformation (P chirality, dihedral angle phi = 90 +/- 10 degrees) dominate. The amide backbone CD contribution varies over all temperatures (-80 degrees to +80 degrees C) providing evidence for a type-II beta-turn at low temperatures, with the emergence of a type-I beta-turn at higher temperatures. Tyrosine exhibits a special behaviour at pH 7. These conclusions are in broad agreement with published NMR studies. Nevertheless, the MCH(5-14) core is seen to be conformationally flexible in aqueous solution at ambient temperatures. Conformation differences are observed in a non-aqueous environment.
Siligardi
G
G
Department of Chemistry, University of Calabria, Arcavacata di Rende (CS), Italy.
Campbell
M M
MM
Gibbons
W A
WA
Drake
A F
AF
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D004220:Disulfides; D006863:Hydrogen-Ion Concentration; D007028:Hypothalamic Hormones; D008543:Melanins / Q000737:chemistry*; D008969:Molecular Sequence Data; D010907:Pituitary Hormones / Q000737:chemistry*; D011487:Protein Conformation; D013816:Thermodynamics; D014443:Tyrosine
D004220:Disulfides; D007028:Hypothalamic Hormones; D008543:Melanins; D010907:Pituitary Hormones; D014443:Tyrosine; C019463:melanin-concentrating hormone