Engineering and exploiting synthetic allostery of NanoLuc luciferase

The ability to endow constitutively active proteins with synthetic allostery is a central objective of Synthetic Biology, mostly focused on the creation of protein biosensors – artificial sensing proteins with easily quantifiable outputs. Here we hypothesize that circular permutation of proteins increases the probability of functional coupling of new N- and C- terminal sequences with the active center of the protein through increased local structural disorder. We test this by constructing a synthetically allosteric version of circular permutated NanoLuc luciferase, activated through ligand-induced intramolecular non-covalent cyclisation. The developed biosensors cover a range of emission wavelengths and display sensitivity as low as 50 pM and dynamic range as high as 16-fold and could quantify their cognate ligand in human fluids such as saliva, serum and lysed blood. We apply hydrogen exchange kinetic mass spectrometry to analyze time resolved structural changes in the developed biosensors and observed ligand-mediated folding of newly created termini. While a large study is required for determining how frequent synthetic allostery emerges following circular permutation and what types of protein folds are susceptible to it, this study provides motivation and justification for such efforts.