title: Novel fusion protein approach for efficient high-throughput screening of small molecule-mediating protein-protein interactions in cells and living animals.
abstract: Networks of protein interactions execute many different intracellular pathways. Small molecules either synthesized within the cell or obtained from the external environment mediate many of these protein-protein interactions. The study of these small molecule-mediated protein-protein interactions is important in understanding abnormal signal transduction pathways in a variety of disorders, as well as in optimizing the process of drug development and validation. In this study, we evaluated the rapamycin-mediated interaction of the human proteins FK506-binding protein (FKBP12) rapamycin-binding domain (FRB) and FKBP12 by constructing a fusion of these proteins with a split-Renilla luciferase or a split enhanced green fluorescent protein (split-EGFP) such that complementation of the reporter fragments occurs in the presence of rapamycin. Different linker peptides in the fusion protein were evaluated for the efficient maintenance of complemented reporter activity. This system was studied in both cell culture and xenografts in living animals. We found that peptide linkers with two or four EAAAR repeat showed higher protein-protein interaction-mediated signal with lower background signal compared with having no linker or linkers with amino acid sequences GGGGSGGGGS, ACGSLSCGSF, and ACGSLSCGSFACGSLSCGSF. A 9 +/- 2-fold increase in signal intensity both in cell culture and in living mice was seen compared with a system that expresses both reporter fragments and the interacting proteins separately. In this fusion system, rapamycin induced heterodimerization of the FRB and FKBP12 moieties occurred rapidly even at very lower concentrations (0.00001 nmol/L) of rapamycin. For a similar fusion system employing split-EGFP, flow cytometry analysis showed significant level of rapamycin-induced complementation.
authors.affiliation: Molecular Imaging Program at Stanford, Department of Radiology and the Bio-X Program, Stanford University School of Medicine, James H. Clark Center, Stanford, California 94305-5427, USA. paulmurg@stanford.edu
authors.forename: Ramasamy
authors.initials: R
authors.lastname: Paulmurugan
authors.forename: Sanjiv S
authors.initials: SS
authors.lastname: Gambhir
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D049452:Green Fluorescent Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D049410:Luciferases, Renilla / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D051379:Mice; D008819:Mice, Nude; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000032:analysis* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D020123:Sirolimus / Q000494:pharmacology; D022021:Tacrolimus Binding Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D014162:Transfection
chemical_list: D011506:Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D049410:Luciferases, Renilla; D022021:Tacrolimus Binding Proteins; D020123:Sirolimus