Design and conformational analysis of natively folded β-hairpin peptides stabilized by nucleobase interactions

To examine stabilizing effects of the base pair interaction on a protein scaffold, various peptides with L-α-amino acids bearing a nucleobase in the side chain (nucleobase amino acids; NBAs) were designed based on a G-peptide β-hairpin structure, and their conformational properties were investigated by circular dichroism and NMR spectroscopy. Thermodynamic analyses based on the chemical shifts showed that adenine-thymine pairing in a diagonal fashion at positions 4 and 15 (2AT) enhanced thermal stability of the peptide conformation by more than 30 K as compared with the wild-type G-peptide. In NOESY spectrum, not only numerous nonadjacent crosspeaks but also long-range crosspeaks between the nucleobases were observed in some peptides with the base pairing. NMR structure calculations of the 2AT peptide confirmed that cross-strand pairing of the nucleobases occurs on the well-defined β-hairpin structure as designed. Taken together, the base pairing in an appropriate position and orientation facilitates folding and stabilization of a native-like β-hairpin structure.