Mechanism of the Activation of Proteinase Inhibitor Synthesis by Systemin Involves β−Sheet Structure, a Specific DNA−Binding Protein Domain

We analyzed a tertiary structure of systemin, the first identified polypeptide plant hormone, using two−dimensional NMR spectroscopy. From these data and molecular dynamics calculations we concluded that the peptide can adopt a Z−like−β−sheet structure, which has previously been found in many specific DNA−binding proteins. Using DNA−cellulose affinity chromatography, we showed that systemin binds strongly to DNA. We suggest that the specific systemin−DNA interaction, particularly in a promoter region of the proteinase inhibitors, could effect gone expression and thus explain the biological activity of systemi