Beta-hairpin stabilization in a 28-residue peptide derived from the beta-subunit sequence of human chorionic...

The beta-subunit of the human chorionic gonadotropin (hCG) hormone, which is believed to be related to certain types of cancer, contains three hairpin-like fragments. To investigate the role of beta-hairpin formation in the early stages of the hCGbeta folding, a 28-residue peptide with the sequence RDVRFESIRLPGSPRGVNPVVSYAVALS, corresponding to the H3-beta hairpin fragment (residues 60-87) of the hCGbeta subunit, was studied under various conditions using three optical spectroscopic methods: Fourier transform ir spectroscopy, electronic CD, and vibrational CD. Environmental conditions are critical factors for formation of secondary structure in this peptide. TFE : H(2)O mixed solvents induced helical formation. Formation of beta-structure in this peptide, which may be related to the native beta-hairpin formation in the intact hormone, was found to be induced only under conditions such as high concentration, high temperature, and the presence of nonmicellar sodium dodecyl sulfate concentrations. These findings support a protein folding mechanism for the hCGbeta subunit in which an initial hydrophobic collapse, which increases intermolecular interactions in hCGbeta, is needed to induce the H3-beta hairpin formation.