The LytC lysozyme of Streptococcus pneumoniae is a bacterial cell wall hydrolase that cleaves the beta1-4-glycosydic bond located between the N-acetylmuramoyl-N-glucosaminyl residues of the cell wall polysaccharide chains. LytC is composed of a C-terminal glycosyl hydrolase family 25 (GH25) domain and an N-terminal choline-binding module (CBM) consisting of eleven homologous repeats that specifically recognizes the choline residues of pneumococcal lipoteichoic and teichoic acids. This domain arrangement is the reverse of the major pneumococcal autolysin, LytA, and the CPL-1-like lytic enzymes of the pneumococcal bacteriophages, in which the CBM (consisting of six repeats) is at the C-terminus. This model represents the C-terminal catalytic domain of the LytC-like enzymes.

Endo-N-acetylmuramidases (muramidases) are lysozymes (also referred to as peptidoglycan hydrolases) that degrade bacterial cell walls by catalyzing the hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues. This family of muramidases contains a glycosyl hydrolase family 25 (GH25) catalytic domain and is found in bacteria, fungi, slime molds, round worms, protozoans and bacteriophages. The bacteriophage members are referred to as endolysins which are involved in lysing the host cell at the end of the replication cycle to allow release of mature phage particles. Endolysins are typically modular enzymes consisting of a catalytically active domain that hydrolyzes the peptidoglycan cell wall and a cell wall-binding domain that anchors the protein to the cell wall. Endolysins generally have narrow substrate specificities with either intra-species or intra-genus bacteriolytic activity.

PlyB is a bacteriophage endolysin that displays potent lytic activity toward Bacillus anthracis. PlyB has an N-terminal glycosyl hydrolase family 25 (GH25) catalytic domain and a C-terminal bacterial SH3-like domain, SH3b. Both domains are required for effective catalytic activity. Endolysins are produced by bacteriophages at the end of their life cycle and participate in lysing the bacterial cell in order to release the newly formed progeny. Endolysins (also referred to as endo-N-acetylmuramidases or peptidoglycan hydrolases) degrade bacterial cell walls by catalyzing the hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues.

Lyzozyme M1 (1,4-beta-N-acetylmuramidase), GH25 family [Cell wall/membrane/envelope biogenesis].

Glycosyl hydrolases family 25.

3D-structureof the modular autolysin LytC from Streptococcus pneumoniae at 1.6 A resolution [Streptococcus pneumoniae R6],2WWD_A 3D-structure of the modular autolysin LytC from Streptococcus pneumoniae in complex with pneummococcal peptidoglycan fragment [Streptococcus pneumoniae R6]

3D-structureof the modular autolysin LytC from Streptococcus pneumoniae in complex with synthetic peptidoglycan ligand [Streptococcus pneumoniae R6]