Conformational transitions in beta-structured peptides induced by interaction with DNA

Conformational transitions of synthetic 16-mer linear and cyclic peptides c apable of forming beta-hairpins were studied in solution and upon interacti on with DNA. In the cyclic peptide, the beta-hairpin structure is stabilize d by an S-S-bond between two cysteine residues. It was shown that both pept ides in aqueous solution contain about 30-40% of a beta-conformation along with a chaotic one. In 20 and 40% aqueous trifluoroethanol (TFE), the secon dary structure of the protein is stabilized owing to an increase in the alp ha- and beta-conformation content. Upon interaction with DNA in 20% TFE, co nformational changes are observed in both peptides whereas the DNA structur e is not substantially affected. The conformational changes result in an in crease in the content of the alpha-helical conformation. In complexes of th e linear peptide with DNA in 20% TFE at a peptide-basepair ratio of 2:4, th e content of the beta-sheet increases considerably. It is shown that the tr ansition from disordered and alpha-helical conformations to a beta-sheet up on linear peptide-DNA binding does not depend on the DNA nucleotide composi tion. This transition is weakly expressed in DNA-cyclic peptide complexes a nd is virtually absent in aqueous solution and 40% TFE.