Light Activated BioID (LAB): an optically activated proximity labeling system to study protein-protein interactions.

Proximity labeling with genetically encoded enzymes are widely used to study protein-protein interactions in cells. However, the accuracy of proximity labeling is limited by a lack of control over the enzymatic labeling process. Here, we present a light-activated proximity labeling technology for mapping protein-protein interactions at the cell membrane with high accuracy and precision. Our technology, called Light Activated BioID (LAB), fuses the two halves of the split-TurboID proximity labeling enzyme to the photodimeric proteins CRY2 and CIB1. We demonstrate in multiple cell lines, that upon illumination with blue light, CRY2 and CIB1 dimerize, reconstitute split-TurboID, and initiate biotinylation. Turning off the light dissociates CRY2 and CIB1 and halts biotinylation. We benchmark LAB against the widely used TurboID proximity labeling method by measuring the proteome of E-cadherin, an essential cell-cell adhesion protein. We show that LAB can map E-cadherin binding partners with higher accuracy and significantly fewer false positives compared to TurboID.