Display of aggregation-prone ligand binding domain of human PPAR gamma on surface of bacteriophage lambda

Aim: To display the aggregation-prone ligand binding domain (LBD) of the human peroxisome proliferator-activated receptor gamma (PPAR gamma) on the surface of bacteriophages to establish an easy screening assay for the identification of PPAR gamma ligands. Methods: Plasmids were constructed for the expression of the PPAR gamma LBD as a fusion to the N-terminus of the g3p protein of filamentous phage or the C-terminus of the capsid protein D (pD) of phage lambda. The fusion proteins were expressed in E coli and solubility characteristics were compared. Polyclonal antibodies against the LBD as well as the pD protein were prepared for Western blot analysis and phage capture assay. Results: The pD-LBD fusion protein was partially soluble, whereas the LBD-g3p fusion protein was detected only in the insoluble fraction. The pD-LBD fusion protein was efficiently incorporated in phage particles. Furthermore, the LBD was shown to be displayed on the surface of bacteriophage lambda. On average, the pD-LBD fusion protein accounted for 28% of the total pD protein in the lambda head capsid. Conclusion: The hydrophobic PPAR gamma LBD was expressed as a soluble form of fusion protein in E coli and displayed on the surface of bacteriophage lambda when it was fused to the lambda pD protein. The lambda pD fusion system could be used for improving the solubility of proteins that tend to form inclusion bodies when expressed in E coli. The lambda phage particles displaying the LBD of PPAR gamma may be of great value for the identification of novel PPAR gamma ligands.