Engineering endolysins as antibacterial biologics: protein engineering design strategies and trade-offs

Endolysins, the phage murein hydrolases, are promising alternatives to conventional antibiotics. They are highly target specific, rarely induce resistance and spare commensal microbiota. Synergy between endolysins and certain antibiotics has also been well documented, which further supports their therapeutic potential. However, clinical translation is constrained by protein instability, immunogenicity, limited Gram-negative bactericidal activity and short in vivo half-life. This narrative review examines protein engineering strategies for endolysin development and reconciles conflicting mechanistic observations in the literature. It proposes a trade-off framework and context-dependent design principles for engineering next-generation endolysin-based therapeutics.