Helix and hairpin nucleation in short peptides using centrally positioned conformationally constrained dipeptide segments?

Organic & Biomolecular Chemistry Pub Date: 2012-01-26 DOI: 10.1039/C2OB06817F

Abstract

The effect of incorporation of a centrally positioned Ac6c-Xxx segment where Xxx = LVal/DVal into a host oligopeptide composed of L-amino acid residues has been investigated. Studies of four designed octapeptides Boc-Leu-Phe-Val-Ac6c-Xxx-Leu-Phe-Val-OMe (Xxx = DVal 1, LVal 2) Boc-Leu-Val-Val-Ac6c-Xxx-Leu-Val-Val-OMe (Xxx = DVal 3, LVal 4) are reported. Diagnostic nuclear Overhouse effects characteristic of hairpin conformations are observed for Xxx = DVal peptides (1 and 3) while continuous helical conformation characterized by sequential NiH ? Ni+1H NOEs are favored for Xxx = LVal peptides (2 and 4) in methanol solutions. Temperature co-efficient of NH chemical shifts are in agreement with distinctly different conformational preferences upon changing the configuration of the residue at position 5. Crystal structures of peptides 2 and 4 (Xxx = LVal) establish helical conformations in the solid state, in agreement with the structures deduced from NMR data. The results support the design principle that centrally positioned type I β-turns may be used to nucleate helices in short peptides, while type I′ β-turns can facilitate folding into β-hairpins.

Graphical abstract: Helix and hairpin nucleation in short peptides using centrally positioned conformationally constrained dipeptide segments
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