The chimera QSLA, built on a novel clue to create lysin-based superior antibacterials, turned out to be one of the most lethal lysins against Streptococcus pneumoniae and related pathogens in vitro (A) and in vivo (B)

Bacterial resistance to the most commonly used antibiotics is nowadays a major social and economic challenge. In this scenario, cell wall lysins are a new class of antibacterial, ranked among the top alternatives to fight against multi-resistant pathogenic bacteria. Lysins break down the cell wall of bacteria when applied externally, causing bacterial death by osmotic shock. To the unique properties they offer as antibacterials, lysins add a huge panoply of available sequences with different host specificities which are easily engineered to create novel enzymes with custom properties. Here, we have investigated whether the acquisition of enzymatic active domains (EADs) and cell wall binding domains (CBDs) of compensatory efficiencies is one of the factors that may contribute to fine-tuning the lytic activity of natural lysins, since corroboration of this point would pave the way towards creating superior custom-made lysins. The rationale was applied to produce a chimeric lysin of superior antibacterial capacity using two well-characterized lysins: the endolysin Skl and the major pneumococcal autolysin LytA. The combination of Skl EAD and the CBD of LytA in the QSLA chimera increased bacterial clearance 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, the chimera QLAS, containing LytA EAD and Skl CBD, was inactive against all tested strains, although domain structures were preserved and hydrolysis of purified cell walls was 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. Gallego-Páramo, N. Hernández-Ortiz, P. García, M. Menéndez. (2022) Interrogation of the contribution of (endo)lysin domain to tune their bacteriolytic efficiency provides a novel clue to design superior antibacterials. Int. J. Biol. Macromol. 223: 1042-1053. doi: 10.1016/j.jibiomac.2022.11.043