Towards XNA molecular biology: Bacterial cell display as a robust and versatile platform for the engineering of low affinity ligands and enzymes

Although directed evolution has been remarkably successful at expanding the chemical and functional boundaries of biology, it is limited by the robustness and flexibility of available selection platforms - traditionally designed around a single desired function with limited scope for alternative applications. We report SNAP as a quantitative reporter for bacterial cell display, which enabled fast troubleshooting and systematic development of the selection platform. In addition, we demonstrate that even weak interactions between displayed proteins and nucleic acids can be harnessed towards specific labelling of bacterial cells, allowing functional characterisation of DNA binding proteins and enzymes. Together, this establishes bacterial display as a viable route towards the systematic engineering of all ligands and enzymes required for the development of XNA molecular biology.