Lytic transglycosylases.

Although cleaving the same glycosidic bond between MurNAc and GlcNAc in murein, lytic transglycosylases differ from lysozymes by catalyzing an intramolecular transglycosylation of the glycosyl-bond onto the C6 hydroxyl group of the muramic acid residue yielding 1.6-anhydromuramic acid-carrying products. The three dimensional structure of the soluble lytic transglycosylase Slt70 of E. coli revealed a doughnut-like shape that would allow the protein to encircle the polysaccharide strands of the murein. Despite the absence of significant sequence homology, the catalytic center shows structural similarity to lysozymes, although the catalytic aspartate is missing. All lytic transglycosylases which have been characterized up until now turned out to be processive exo-glycosylases.