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• Author: Anthony J. Clarke
• Responsible Curator: Anthony J. Clarke

Substrate specificities

Figure 1. Reaction catalyzed by family GH104 enzymes. LT, lytic transglycosylase. (click to enlarge).

These enzymes cleave the β-1,4 linkage between N-acetylmuramoyl and N-acetylglucosaminyl residues in peptidoglycan (Figure 1). No other activities have been observed.

Kinetics and Mechanism

The lytic transglycosidases, strictly speaking, are retaining enzymes. However, they are not hydrolases but rather catalyse an intramolecular glycosyl transferase reaction onto the C-6 hydroxyl group of the muramoyl residue leading to the generation of a terminal 1,6-anhydromuramoyl product (Figure 1) thus lacking a reducing end [2]. No detailed analyses involving either steady state or pre-steady state kinetic studies have been reported.

Catalytic Residues

As with other lytic transglycosylases (families GH23, GH102, and GH103), the GH104 enzymes are thought to possess a single catalytic general acid/base residue. This residue in lambda bacteriophage lytic transglycosylase has been inferred as Glu19 by X-ray crystallography of the enzyme alone [3] and in complex with two chitohexaose oligomers [4]. The role of an essential carboxyl group in the enzyme was confirmed by chemical modification [4], thus supporting the identification of Glu19. The mechanism of action of the family GH104 enzymes has not been investigated and hence it is not known if they follow that of the lytic transglycosylases of families GH23, GH102, or GH103.

Three-dimensional structures

The three-dimensional structure of only the lambda phage enzyme has been solved [3, 4], and like the other lytic transglycosylases of families GH23, and GH103, it possesses the well characterized α+β “lysozyme fold.”

Family Firsts

First identification of lytic transglycosylase

Bacteriophage lambda [3].

First catalytic nucleophile identification

Not applicable for lytic transglycosylases.

First general acid/base residue identification

Inferred by X-ray crystallography of lambda bacteriophage [3].

First 3-D structure

Lambda bacteriophage [3].

References

1. Blackburn NT and Clarke AJ. Identification of four families of peptidoglycan lytic transglycosylases. J Mol Evol 2001 Jan; 52(1) 78-84. pmid:11139297. PubMed HubMed [1]
2. Höltje JV, Mirelman D, Sharon N, and Schwarz U. Novel type of murein transglycosylase in Escherichia coli. J Bacteriol 1975 Dec; 124(3) 1067-76. pmid:357. PubMed HubMed [2]
3. Evrard C, Fastrez J, and Declercq JP. Crystal structure of the lysozyme from bacteriophage lambda and its relationship with V and C-type lysozymes. J Mol Biol 1998 Feb 13; 276(1) 151-64. doi:10.1006/jmbi.1997.1499 pmid:9514719. PubMed HubMed [3]
4. Leung AK, Duewel HS, Honek JF, and Berghuis AM. Crystal structure of the lytic transglycosylase from bacteriophage lambda in complex with hexa-N-acetylchitohexaose. Biochemistry 2001 May 15; 40(19) 5665-73. pmid:11341831. PubMed HubMed [4]