Conformation of a water-soluble beta-sheet model peptide. A circular dichroism and Fourier-transform infrared spectroscopic study of double D-amino acid replacements.

Among peptide secondary structures beta-sheet domains have been much less intensively studied than alpha-helical conformations, mainly because of the lack of well characterized model peptides. In the present paper the secondary structure of a water-soluble de novo peptide consisting of 26 amino acids (DPKGDPKGVTVTVTVTVTGKGDPKPD-NH2) and the corresponding double D-amino acid replacement set have been studied by circular dichroism and Fourier-transform infrared spectroscopy. The model peptide was found to be unstructured in aqueous solution at peptide concentrations < 10(-3) mol/L but to adopt a predominantly beta-sheet structure in the presence of 15 mM sodium dodecyl sulfate or at apolar/water interfaces. Although the peptide is composed of amino acids with low helical propensity, it formed a single-stranded helical structure in aqueous trifluoroethanol. The D-amino acid replacement set was synthesized in order to study the conformational stability of the model peptide selectively in distinct regions. The data show that both the alpha-helix present in 50% trifluoroethanol as well as the beta-sheet domain formed in the presence of sodium dodecyl sulfate or at apolar/water interfaces, are located in the region between Val9 and Thr18. Pairwise substitution of adjacent amino acids by their corresponding D-amino acids provides a pronounced beta-sheet disturbance. These findings demonstrate that double D-amino acid replacements may be used to locate beta-sheet domains in peptides.