“…Several enzymes have been discovered that can perform selective post-translational covalent modifications of proteins by attaching a molecular probe. Examples of such enzyme-based conjugation methods are biotin ligase (AP-tag) [5] , E2 small ubiquitin-like modifierconjugating enzyme Ubc9 (LACE-tag) [6], lipoic acid ligase (LAP-tag) [7] , AnkX [8] , transglutaminases (Qtag) [9,10] , sortase [11][12][13][14] and tubulin tyrosine ligase (Tub-tag) [15] . However, most of these methods rely on 2 (complex) synthetic fluorescent probes that are often not biocompatible.…”