FRET-based biosensors couple ligand-dependent protein conformational changes to a fluorescent signal response. Such biosensors can be used intra- or extracellularly to provide rapid, real-time responses to ligands or metabolites of interest. Unlike typical reporter systems, signals from FRET biosensors are reversible, permitting detection of anabolic and catabolic (conversion) processes and variations in metabolite fluxes. FRET biosensors can be constructed from a variety of metabolite binding proteins. A suite of fluorescent protein scaffolds has been constructed to rapidly identify FRET-responsive ligand binding domains and for optimization of FRET biosensors. The biosensors are ratiometric and respond to changes in the emission characteristics of the sensor upon the binding of a ligand. Signals are independent of biosensor concentration. They perform in vitro as well as in vivo. This approach is useful for high-throughput screening and sorting and is adaptable for use in the monitoring of bioreactor titers in real time. A prerequisite is the need a protein assembly that changes conformation upon binding of a desired ligand. Libraries of these exist in nature in the form of solute binding proteins and technology has been recently adapted to domains of certain types of transcription factors. Sensors for a variety of metabolites are available and new sensors directed towards new metabolites could be readily developed through collaboration.
Argonne National Laboratory