Domain shuffling and module engineering of Listeria phage endolysins for enhanced lytic activity and binding affinity.

Bacteriophage endolysins are peptidoglycan hydrolases employed by the virus to lyse the host at the end of its multiplication phase. They have found many uses in biotechnology; not only as antimicrobials, but also for the development of novel diagnostic tools for rapid detection of pathogenic bacteria. These enzymes generally show a modular organization, consisting of N-terminal enzymatically active domains (EADs) and C-terminal cell wall-binding domains (CBDs) which specifically target the enzymes to their substrate in the bacterial cell envelope. In this work, we used individual functional modules of Listeria phage endolysins to create fusion proteins with novel and optimized properties for labelling and lysis of Listeria cells. Chimaeras consisting of individual EAD and CBD modules from PlyPSA and Ply118 endolysins with different binding specificity and catalytic activity showed swapped properties. EAD118-CBDPSA fusion proteins exhibited up to threefold higher lytic activity than the parental endolysins. Recombineering different CBD domains targeting various Listeria cell surfaces into novel heterologous tandem proteins provided them with extended recognition and binding properties, as demonstrated by fluorescent GFP-tagged CBD fusions. It was also possible to combine the binding specificities of different single CBDs in heterologous tandem CBD constructs such as CBD500-P35 and CBDP35-500, which were then able to recognize the majority of Listeria strains. Duplication of CBD500 increased the equilibrium cell wall binding affinity by approximately 50-fold, and the enzyme featuring tandem CBD modules showed increased activity at higher ionic strength. Our results demonstrate that modular engineering of endolysins is a powerful approach for the rational design and optimization of desired functional properties of these proteins.