SECONDARY STRUCTURE OF A HUMAN GROWTH HORMONE-RELEASING FACTOR FRAGMENT (LEU(27)-HGRF(15-32)NH2) IN AQUEOUS SDS MICELLE ENVIRONMENTS

The secondary structure of a human growth hormone-releasing factor (hG RF) fragment (Leu27-hGRF(15-32)NH2) has been studied by H-1 NMR at 500 MHz in aqueous solutions containing varying concentrations of d25-sod ium dodecyl sulfate (SDS). Chemical shifts, coupling constants and NOE SY data show that the secondary structure of the peptide is random in aqueous solution in the absence of SDS. At relatively low molar ratios of SDS to peptide (1.3:1 to 3.3:1 SDS:peptide) the 1D H-1 spectrum of the peptide changes as the peptide resonances are broadened significa ntly. NOESY patterns consistent with helical structure are present in the region of residues 22-29 when the SDS:peptide molar ratio is 1.3:1 and the SDS concentration is slightly below the critical micelle conc entration (CMC). At higher molar ratios of SDS to peptide (16:1 to 72: 1), where the SDS concentration is significantly above the CMC, the li neshape of the peptide's H-1 NMR spectrum is sharpened In these enviro nments an alpha-helical conformation is induced in residues 19-32 of t he hGRF fragment, as shown both by NOESY and by chemical shift data. T hus, the well-known tendency of this region of the GRF peptide to form alpha-helix in isotropic mixed-solvent systems (e.g., methanol/water trifluoroethanol (TFE)/water) is seen also in SDS/aqueous systems.