Systematic mapping of orthogonality and domain-swap permissiveness across LysR-type transcriptional biosensors
Transcription factor-based biosensors monitor metabolites and control genetic programs, but their wider use is constrained by the limited repertoire of characterized, mutually compatible sensor parts. Here we combine a curated screen of natural LysR-type transcriptional regulators (LTTRs), the largest family of bacterial transcription factors, with systematic domain swapping. Using a standardized construction platform, we convert 17 LTTRs into whole-cell reporters in Escherichia coli. Of 16 viable circuits, nine show regulatory activity, including six ligand-inducible biosensors for acetate, benzoate, -ketoglutarate, chlorohydroquinone, L-homocysteine and salicylate. Mapping interactions across 11 LTTR systems identifies seven mutually orthogonal regulator pairs, providing, to our knowledge, the first orthogonality map for this family. We next construct 108 chimeras across three domain-swap architectures; 69 retain measurable activity, with functional outcomes enriched when the native hinge-ligand-binding-domain association is preserved. As proof of principle, we redesign a cross-reactive regulator: replacing its DNA-binding domain with one from an orthogonal regulator abolishes unwanted promoter crosstalk while preserving ligand-inducible activation of its own target, transferring orthogonality to a previously incompatible pair. Together, natural-diversity screening and domain swapping emerge as complementary routes to expand LTTR biosensor repertoires, revealing a strong link between connector architecture and chimera function.