Conformational preferences for the peptides SRPINATLAVEKEGSPVSITVNTTISA (H1) and APTMTRVLQGVLPALPQVVCNYR (H2) corresponding to the amino acid residues 9-35 and 38-60, respectively, of the glycoprotein hormone human chorionic gonadotropin β-subunit (hCGβ) were studied by Fourier transform infrared spectroscopy (FTIR) and vibrational and electronic circular dichroism (VCD and ECD) in various environments. These peptides correspond to the H1 (β-like) and H2 (loop) hairpins of the native-state hCGβ subunit defined by X-ray analysis. As demonstrated by FTIR and VCD, the H1 peptide adopts a β-structure in water as well as in environments that normally induce α-helix formation, such as mixed trifluoroethanol/H2O solvent or micellar concentrations of sodium dodecyl sulfate. By contrast, the H2 peptide ECD and VCD spectra are consistent with a significant fraction of the residues being in either a poly-L-proline II like or a partially helical conformation depending on the environment. A third peptide, H3, corresponding to the 60-87 hairpin region of hCGβ, which was studied previously, switches its conformation depending on both the solvent and peptide concentration. Taken together, the data suggest that hCGβ may fold by, first, the H1 region rapidly adopting a β-hairpin structure, followed by its hydrophobic collapse with the H3 region, which in turn facilitates the formation of the H3 β-hairpin. The H2 hairpin loop is formed as a result of the formation of the H1 and H3 β-hairpin interactions.
ASJC Scopus subject areas
- Colloid and Surface Chemistry