Scheme 2

Target Identification (ID) using tetrazine ligation. Top flow : Target ID probe with photocleavable linker is incubated with proteome and binds to target protein. The target protein is conjugated to beads with tetrazine ligation for purification. The bound proteins are photo-cleaved from the beads and analyzed by LC-MS/MS. Bottom flow : Target ID probe with photoaffinity linker is incubated with proteome and binds to target protein. UV irradiation generates a covalent bond between target protein and the probe. The proteins are conjugated to beads with tetrazine ligation for purification. The bound proteins are denatured and eluted from the beads, followed by MS analysis