Glasgow, A. A. et al. Science 366, 1024–1028 (2019).

The ability to sense small molecules with high sensitivity and specificity has yielded important insights into biology. Although fluorescent protein-based sensors for a wide range of small molecules have been developed, these often rely on specific cellular proteins that have evolved to bind the ligand of interest, and therefore broadly general strategies for making new sensors are lacking. Glasgow et al. have harnessed the power of computational protein design to address this challenge. In their approach, a binding site for a small molecule is designed and engineered into the binding interface of two proteins such that they only dimerize in the presence of the target molecule. These proteins are also fused to two halves of a split luminescent or fluorescent reporter, and only upon target binding and dimerization does the split reporter interact to yield signal. The researchers developed sensors against multiple targets and further showed that the crystal structures with bound ligand closely match the computational predictions.