Sequential oligopeptides containing lysene: Synthesis, circular dichroism, conformation and complexes with DNA

Abstract

Oligomeric (Lys-Ala-Ala)1-5 and (Lys-Leu-Ala)1-4 were synthesized by fragment condensation in solution, (Lys-Ala-Ala)10Ape was obtained by stepwise synthesis from the tripeptide monomer on a polymeric carrier. Conformation of the compounds in water, aqueous methanol and trifluoroethanol was studied by CD spectroscopy. The dimer and trimer in both the structural series show no signs of α-helix formation. The higher oligopeptides exist in random conformation in aqueous solutions, whereas in the presence of alcohols they are partly in the α-helical conformation, depending on the chain length and the character and concentration of the alcohol. However, the ability of α-helix formation is substantially lower even for the studied decamer than for polytripeptides of DP ~30 and higher. According to the CD spectra, the conformational changes resulting from interaction of the oligopeptides with DNA are generally small for both components. The changes of DNA structure may be interpreted as winding of the double helix. The oligopeptide conformation is very little affected by the complexation and is invariably random, contrary to that of the corresponding polypeptides which in complexes with DNA are at least partially α-helical.