ABSTRACT
Etoposide (VP-16) is an anti-tumor compound that targets topoisomerase II (top II). In this study, we have identified an alternative binding protein of etoposide by screening a library of T7 phage-displayed peptides. After four rounds of selection using a biotinylated etoposide derivative immobilized on a streptavidin-coated plate, T7 phage particles that display a 16-mer peptide NSSASSRGNSSSNSVY (ETBP16) or a 10-mer NSLRKYSKLK (ETBP10) were enriched with the ratio of 40 or 11 out of the 69 clones, respectively. Binding of etoposide to these peptides was confirmed by surface plasmon resonance (SPR) analysis, which showed ETBP16 and ETBP10 to have a kinetic constant of 4.85 × 10â»5 M or 6.45 × 10â»5 M, respectively. ETBP16 displays similarity with the ser-rich domain in E2F-4, a transcription factor in cell cycle-regulated genes, suggesting that etoposide might interact with E2F-4 via this domain. SPR analysis confirmed the specific binding of etoposide to recombinant E2F-4 is in the order of 10â»5 M. Furthermore, etoposide was shown to inhibit luciferase reporter gene expression mediated by the heterodimeric E2F-4/DP complex. Taken together, our results suggest that etoposide directly binds to E2F-4 and inhibits subsequent gene transcription mediated by heterodimeric E2F-4/DP complexes in the nucleus.
Subject(s)
Carrier Proteins/metabolism , E2F Transcription Factors/metabolism , Etoposide/metabolism , Peptide Library , Amino Acid Sequence , Animals , Bacteriophage T7/metabolism , Biotinylation , CHO Cells , Cricetinae , Cricetulus , Drug Screening Assays, Antitumor , E2F Transcription Factors/genetics , Etoposide/analogs & derivatives , Etoposide/chemical synthesis , Etoposide/chemistry , Gene Expression Regulation , Genes, Reporter/genetics , Humans , Molecular Sequence Data , Peptides/chemistry , Peptides/metabolism , Protein Binding , Sequence Alignment , Structure-Activity RelationshipABSTRACT
Clarithromycin is a macrolide antibiotic that is widely used in clinical medicine. Macrolide antibiotics such as clarithromycin specifically bind to the 50S subunit of the bacterial ribosome thereby interfering with protein biosynthesis. A selected peptide sequence from our former study, composed of 19 amino acids, which was isolated from a phage display library because of its ability to bind clarithromycin, displayed significant similarity to a portion of the human_p8 protein. The recombinant p8 protein binds to biotinylated-clarithromycin immobilized on a streptavidin-coated sensor chip and the dissociation constant was determined. The binding of recombinant p8 protein to double-stranded DNA was inhibited by biotinylated-clarithromycin, clarithromycin, erythromycin and azithromycin in gel mobility shift assay. Dechlorogriseofulvin, obtained from a natural product screening, also inhibited human p8 protein binding to DNA. This study illustrates the general utility of the phage display method in detecting protein-ligand interactions.
