Interrogation of the contribution of (endo)lysin domains to tune their bacteriolytic efficiency provides a novel clue to design superior antibacterials.

Bacteriophage-derived endolysins and bacterial autolysins (hereinafter lysins) represent a completely new class of efficient antibacterials. They prevent the development of bacterial resistance and help protect commensal microbiota, producing cell wall lysis. Here we have investigated whether the acquisition of enzymatic active domains (EADs) and cell wall binding domains (CWBDs) of balancing efficiencies could be a way of tuning natural lysin activity. The concept was applied to produce a chimeric lysin of superior antibacterial capacity using the endolysin Skl and the major pneumococcal autolysin LytA. Combination of the Skl EAD and the cell wall choline-binding domain (CBD) of LytA in the chimera QSLA increased the bacterial killing by 2 logs or more compared to parental enzymes at an equal concentration and extended the substrate range to resistant and emergent pneumococci and other pathogens of the mitis group. Contrarily, QLAS, containing LytA EAD and Skl CBD, was inactive against all tested strains, although domain structures were preserved and hydrolysis of purified cell walls maintained in both chimeras. As a whole, our study provides a novel clue to design superior lysins to fight multidrug-resistant pathogens based on domain selection, and a powerful in-vivo active lysin (QSLA) with promising therapeutic perspectives.