Lysin

Lysins, also known as endolysins or murein hydrolases, are hydrolytic enzymes produced by host bacteria when infected with bacteriophages in order to cleave the cell wall during the final stage of the lytic cycle to release the viral particles. Lysins are highly evolved enzymes that are able to target one of the five bonds in peptidoglycan (murein), the main component of bacterial cell walls, which allows the release of progeny virions from the lysed cell. Cell-wall-containing Archaea are also lysed by specialized pseudomurein-cleaving lysins, while most archaeal viruses employ alternative mechanisms. Similarly, not all bacteriophages synthesize lysins: some small single-stranded DNA and RNA phages produce membrane proteins that activate the host's autolytic mechanisms such as autolysins. Lysins were first used therapeutically in 2001 and are now being used as antibacterial agents due to their high effectiveness and specificity in comparison with antibiotics, which are susceptible to bacterial resistance. Because lysins are essential for bacteriophage survival, resistance to lysins is an extremely rare event. Over the course of lysin development as therapeutics, resistance has not been observed, even when resistance is forced by mutagenesis experiments.