An <i>E. coli</i> two-hybrid system to investigate human protein-protein interactions

The LexA-<i>E. coli</i> two-hybrid (LexA-E2H) system was initially developed to study interactions between microbial proteins in an <i>Escherichia coli</i> (<i>E. coli)</i> environment. We here demonstrate its utility for studying mammalian protein interactions. Specifically, this study uses LexA-E2H to provide the first direct and quantitative validation of Glucose Regulated Protein 78 (GRP78) binding to the cleaved-Prostate Apoptosis Response 4 (cl-Par-4) tumor suppressor. Furthermore, the results establish that this interaction does not require phosphorylation of either protein. MacConkey agar was used for initial detection of the interaction through colorimetric colony screening, distinguishing pale white-pink colonies (+ interaction) from red colonies (- interaction). This was followed by β-galactosidase assays for quantitative assessment. These results demonstrate the potential of the LexA-E2H system to advance human protein-protein interaction research. LexA-E2H is simple to implement, avoiding the need to culture eukaryotic cells, and bypassing interference from eukaryotic proteins. This system is ideal for laboratories with limited resources and complements conventional eukaryotic methods.