Fig. 3. Combining functions using Spy technology. (A) Combinatorial antibody decoration. A binder library bearing SpyTag can be mixed with a library of effectors bearing SpyCatcher, leading to rapid expansion of functional properties. (B) Multi-enzyme cascade from Spy and Snoop assembly. CsgA-SpyTag forms filaments extending from the cell-surface. The filaments act as a solid-phase, allowing sequential coupling of enzymes for chitin degradation using orthogonal reaction of SpyTag/SpyCatcher and SnoopTag/SnoopCatcher. GlcNAc = N-acetylglucosamine; GlcN = glucosamine. (C) White LED assembly. 3 different fluorescent proteins are ligated by SpyTag/SpyCatcher and SnoopTag/SnoopCatcher reaction, enabling efficient Förster resonance energy transfer (FRET). Encapsulation in a matrix and illumination at 400 nm leads to stable neutral white light emission. BFP = blue fluorescent protein; eGFP = enhanced green fluorescent protein.