Quantitative Analysis of γ-Aminobutyric Acid by Combined Cell-Free Protein Synthesis and Transamination Reactions

The synthetic power of cells can be harnessed for assaying important analytes, as well as for producing biomolecules. In particular, cell-free protein synthesis (CFPS) can be implemented as a signal amplification module for bioassays, while avoiding many problems associated with whole cell-based microbial biosensors. Here, we developed a method for analyzing γ-aminobutyric acid (GABA) by combining the enzymatic conversion of GABA and amino-acid-dependent CFPS. In this method, GABA molecules in the assay sample are used to generate alanine, which is incorporated into signal-generating proteins in the subsequent cell-free synthesis reaction. The activity of cell-free synthesized proteins was successfully used to estimate the GABA concentration in the assay sample. In principle, the developed method could be extended for the analyses of other important bioactive compounds.