Surface Display of Complex Enzymes by In Situ SpyCatcher-SpyTag Interaction.

The display of complex proteins on the surface of cells is of great importance for protein engineering and other fields of biotechnology. We here describe a modular approach, where the membrane anchor protein Lpp-OmpA and a protein of interest (passenger) are expressed independently as genetically fused SpyCatcher and SpyTag units and assembled in situ by post-translational coupling. Using fluorescent proteins, we first demonstrate that this strategy allows for instalment of the construct on the surface of E. coli cells. The scope of our approach was then demonstrated by using three different functional enzymes, the stereoselective ketoreductase Gre2p, the homotetrameric glucose 1-dehydrogenase GDH and the bulky heme and diflavin containing cytochrome P450 BM3 (BM3). In all cases the SpyCatcher-SpyTag method enabled the generation of functional whole-cell biocatalysts, even for the bulky BM3 which could not be displayed by conventional fusion with Lpp-OmpA. Furthermore, by using a GDH variant carrying an internal SpyTag, the system could be used to display an enzyme with unmodified N- and C-termini.