Screening and Application of Ligand-mimicking Peptides

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0ligopeptides can mimic various 3-dimensional structures depending on their amino-acid sequences. On the basis of the idea of mimicking peptides, we tried to mimic the function of a non-peptide ligand with oligopeptides in vivo. First, we constructed a novel phage-random-peptide library by modifying the vector phage Ml3mpl8.This phage library was screened for calmodulin (CaM) - binding peptides, and two oligopeptides (termed peptides 1 and 2 ; WDTVRlSF and WPSLQAlR,respectively) were identified. The two peptides differentially inhibited CaM-dependent kinase I and II (CaM kinase I and Il). Peptide 1 inhibited CaM kinase I but not CaM kinase II,whereas peptide 2 inhibited CaM kinase II,but only partially inhibited CaM kinase I at a more than l0-fold higher concentration. Peptide 1 also inhibited a plant calcium dependent protein kinase (CDPK), whereas peptide 2 did not. The results suggested that the two peptides possibly have different effects on signal transduction pathways mediated by CaM and CDPK in plants.We also developed a transcriptional induction system in transgenic plants because it was thought to be required for the expression of the functionaI peptides in vivo. The system consists of a chimeric transcription factor (GVG) which acts as a strong transactivator only in the presence of glucocorticoid and a promoter recognized by GVG.In an experiment with a luciferase gene as a reporter, the system was found to work effectively in transgenic tobacco and Arabidopsis This system is expected to be useful for the expression of not only the mimicking pepddes but also other genes in transgenic plants.