Probing biomolecular interactions of glutathione transferase M2-2 by using peptide phage display

The interactions between biomolecules and human glutathione transferase M2-2 (GST M2-2) were probed by using 9- and 15-mer combinatorial peptide libraries displayed on phage. The peptide libraries were based on random DNA sequences fused to gIII, a gene that expresses a phage coat protein and thus causes the peptides to be displayed on the surface of phage particles. A peptide sequence was enriched through binding to GST M2-2, which indicated a successful selection. Binding studies with the peptide displayed on phage showed binding specificity. The sequence of the peptide had similarities to segments of proteins in the Swiss-Prot Database, to c-Jun N-terminal kinase (JNK), and to the protein Bcl3. JNK is linked to the regulation of the transcription factor AP-1. Use of cell-based assays of the transcriptional activity of AP-1 allowed a novel coactivation function of GST M2-2 to be demonstrated. Specificity in the activation was indicated by the lack of effect of GST A1-1. No coactivator function of GST M2-2 could be demonstrated in assays with Bcl3. These results suggest that GST M2-2 has biological roles in addition to catalysis of detoxication reactions, and demonstrate the potential of phage display in functional genomics research.