Helix and hairpin nucleation in short peptides using centrally positioned conformationally constrained dipeptide segments |
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Authors: | Chandrappa Siddappa Aravinda Subrayashastry Raghothama Srinivasarao Sonti Rajesh Rai Rajkishor Harini Veldore V Shamala Narayanaswamy Balaram Padmanabhan |
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Affiliation: | Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India. |
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Abstract: | The effect of incorporation of a centrally positioned Ac(6)c-Xxx segment where Xxx = (L)Val/(D)Val into a host oligopeptide composed of l-amino acid residues has been investigated. Studies of four designed octapeptides Boc-Leu-Phe-Val-Ac(6)c-Xxx-Leu-Phe-Val-OMe (Xxx = (D)Val 1, (L)Val 2) Boc-Leu-Val-Val-Ac(6)c-Xxx-Leu-Val-Val-OMe (Xxx = (D)Val 3, (L)Val 4) are reported. Diagnostic nuclear Overhouse effects characteristic of hairpin conformations are observed for Xxx = (D)Val peptides (1 and 3) while continuous helical conformation characterized by sequential N(i)H ? N(i+1)H NOEs are favored for Xxx = (L)Val 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 = (L)Val) 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. |
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