Using enantioselective biosensors to evolve asymmetric biocatalysts.

Evolved enantioselective transcription factors (eTFs) enable massively parallel, dose-response measurement of imine reductase enantiomer concentrations, including variants with exceptional specificity across 300,000+ TFs.

• Why it matters: Slow chromatographic enantiomer separations bottleneck biocatalyst development, limiting how quickly enantioselectivity can be measured and optimized during evolution.
• What they did: Using a massively parallel reporter assay, the study measured dose-response curves for over 300,000 eTF variants responding to an imine precursor and chiral amine products, quantifying sensitivity, selectivity, and dynamic range.
• The result: High-resolution structures explain steric and charge contributions to enantioselectivity, and two eTFs support an ultrahigh-throughput chiral screen to evolve an imine reductase with inverted enantioselectivity.

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