Split Biotin Ligase

The fragments remain inactive when separated, so labeling depends on their recruitment to the same cellular site. Once brought together, they reassemble into an active ligase, creating a local enzymatic signal rather than a broadly distributed one. This dependency makes fragment colocalization the key molecular event linking a candidate interaction or contact to biotin deposition nearby.

The reactive intermediate converts enzyme reassembly into a detectable proximity signal. After the ligase fragments form an active enzyme, the intermediate enables covalent attachment of biotin to nearby proteins. Because the modification is covalent, labeled molecules can later be captured and examined as evidence of the protein neighborhood surrounding the reassembled ligase.

Its readout extends beyond a single binding pair because biotin is attached to proteins near the active, reassembled enzyme. The resulting label therefore reports a local molecular neighborhood at the site where the fragments meet. This feature supports analysis of interaction partners and surrounding proteins, while reducing labeling that occurs away from the region of interest.

A supported workflow includes recruiting the inactive fragments to the cellular location of interest, allowing them to reassemble when that location brings them together, and permitting nearby proteins to receive covalently attached biotin. Researchers then isolate the labeled proteins with streptavidin and identify them using mass spectrometry or imaging, depending on the desired readout.

Streptavidin provides the recovery step because it can isolate proteins carrying the covalently attached biotin. After enrichment, mass spectrometry can identify the labeled proteins and reveal interaction partners or local protein neighborhoods. Imaging offers a complementary way to examine where labeling occurs, connecting the molecular readout with its cellular location.

The approach is useful when researchers need to examine molecular proximity within cells, including protein-protein interactions, organelle contacts, and signaling dynamics. Its split-enzyme design makes fragment colocalization informative, while localized labeling helps focus measurements on the cellular site being studied. These properties support both identification of nearby proteins and visualization of spatially restricted events.