A phage display system designed to detect and study protein–protein interactions

Analysing protein–protein interactions is critical in proteomics and drug discovery. The usage of 2-Hybrid (2λ) systems is limited to an in vivo environment. We describe a bacteriophage 2-Hybrid system for studying protein interactions in vitro . Bait and prey are displayed as fusions to the surface of phage λ that are marked with different selectable drug-resistant markers. An interaction of phages in vitro through displayed proteins allows bacterial infection by two phages resulting in double drug-resistant bacterial colonies at very low multiplicity of infections. We demonstrate interaction of the protein sorting signal Ubiquitin with the Vps9-CUE, a Ubiquitin binding domain, and by the interaction of (Gly-Glu)₄ and (Gly-Arg)₄ peptides. Interruptions of the phage interactions by non-fused (free) bait or prey molecules show how robust and unique our approach is. We also demonstrate the use of Ubiquitin and CUE display phages to find binding partners in a λ-display library. The unique usefulness to 2λ is also described.