Peptide models for β-turns: a circular dichroism study (original) (raw)

1984, International Journal of Peptide Protein Research

The circular dichroism spectra of four 0-turn model peptides, Z-Aib-Pro-Aib-Pro-OMe (l) , Piv-Pro-Aib-NHMe (2), Piv-ProD -Ala-NHMe (3) and Piv-Pro-Val-NHMe (4) have been examined under a wide range of solvent conditions, using methanol, hexafluoroisopropanol and cyclohexane. Type I and Type I1 0-turns have been observed for peptides 1 and 2 respectively, in the solid state, while the ProD -Ala sequence adopts a Type I1 Sturn in a related peptide crystal structure. A class C spectrum is observed for 1 in various solvents, suggesting a variant of a Type I(II1) structure. The Type I1 f3-turn is characterized by a CD spectrum having two positive CD bands at-230 nm and-202 nm, a feature observed in Piv-ProD -Ala-NHMe in cyclohexane and methanol and for Piv-Pro-Aib-NHMe in methanol. Peptide 2 exhibits solvent dependent CD spectra, which may be rationalized by considering Type 11, I11 and V reverse turn structures. Piv-Pro-Val-NHMe adopts n o n a t u r n structures in polar solvents, but exhibits a class B spectrum in cyclohexane suggesting a population of Type I &turns.

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