SPERMINE-INDUCED CONFORMATIONAL-CHANGES OF A SYNTHETIC PEPTIDE

A 14-residue peptide, SBP, was synthesized to study the interactions between polypeptides and biological polyamines, e.g. spermine and its derivatives. Four glutamic acid residues were placed in the sequence in such a way that binding of spermine to the peptide could induce the alpha-helical conformation. SBP was found to form a stable 1:1 complex with spermine in neutral aqueous buffer containing 30% trifluoroethanol at 4-degrees-C. The alpha-helicity (19%) of SBP increased to 38% in the presence of spermine. The increase in alpha-helicity of SBP was strongly dependent on pH with a maximum around pH = 7, suggesting ionic interactions between SBP and spermine. Other structurally related polyamines including spermidine and putrescine were also examined to study the specificity of the complex formation. A number of similar sequence motifs that could interact with spermine were identified in native proteins registered in the protein data bank.