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

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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 systemin.