Secondary structure of a dynamic type I’β‐hairpin peptide

:  A spontaneously folding β-hairpin peptide (Lys-Lys-Tyr-Thr-Val-Ser-Ile-Asn-Gly-Lys-Lys-Ile-Thr-Val-Ser-Ile) and related cyclic (cyclo-Gly-Lys-Tyr-Ile-Asn-Gly-Lys-Ile-Ile-Asn) and linear (Ser-Ile-Asn-Gly-Lys) controls were studied to determine the effects of various factors on secondary structure. Secondary structure was evaluated using circular dichroism (CD) and 1D and 2D 1H nuclear magnetic resonance (NMR). The effects of chemical modifications in the peptide and various solution conditions were investigated to determine their impact on peptide structure. The β-hairpin peptide displayed a CD minimum at 216 nm and a TOCSY i + 1 − i + 2 and i + 2 −i + 3 interaction, confirming the expected structure. Using NMR α-proton (H) chemical shifts, the extents of folding of the β-hairpin and linear control were estimated to be 51 and 25% of the cyclic control (pH 4, 37 °C), which was taken to be maximally folded. Substitution of iso-aspartic acid for Asn reduced the secondary structure dramatically; substitution of aspartic acid for Asn also disrupted the structure. This result suggests that deamidation in unconstrained β-turns may have adverse effects on secondary structure. N-terminal acetylation and extreme pH conditions also reduced structure, while the addition of methanol increased structure.