Pseudomonas aeruginosa Cryptic Prophage Endolysin Is a Highly Active Muramidase

Endolysins are phage-encoded enzymes that cleave the
peptidoglycan
of host bacteria. These enzymes have gained considerable attention
due to their ability to cause cell lysis, making them candidates as
antibacterial agents. Most Pseudomonas aeruginosa genomes, including the common laboratory strains PAO1 and
UCBPP-PA14, contain a cryptic prophage encoding a glycoside hydrolase
family 19 endolysin (named PaGH19Lys in the present
study). Family 19 glycoside hydrolases are known to target peptidoglycan
and chitin-type substrates. PaGH19Lys was not active
toward chitin but exhibited activity toward chloroform-treated Gram-negative
bacteria, displaying ∼10,000-fold higher activity than hen
egg white lysozyme. Analysis of products derived from PaGH19Lys activity toward purified P. aeruginosa peptidoglycan showed that the enzyme catalyzed hydrolysis
of the β-1,4 linkage between N-acetylmuramic
acid and N-acetyl-d-glucosamine, classifying
the enzyme as a muramidase. Finally, the crystal structure of PaGH19Lys was determined and solved to 1.8 Å resolution.
The structure of the enzyme showed a globular α-helical fold
possessing a deep but relatively open catalytic cleft.