Crystal structure of the lytic transglycosylase from bacteriophage lambda in complex with hexa-N-acetylchitohexaose

The three-dimensional structure of the lytic transglycosylase from bacterio phage lambda, also known as bacteriophage lambda lysozyme, complexed to the hexasaccharide inhibitor, hexa-N-acetylchitohexaose, has been determined b y X-ray crystallography at 2.6 Angstrom resolution. The unit cell contains two molecules of the lytic transglycosylase with two hexasaccharides bound. Each enzyme molecule is found to interact with four N-acetylglucosamine un its from one hexasaccharide (subsites A-D) and two N-acetylglucosamine unit s from the second hexasaccharide (subsites E and F), resulting in all six s ubsites of the active site of this enzyme being filled. This crystallograph ic structure, therefore, represents the first example of a lysozyme in whic h all subsites are occupied, and detailed protein-oligosaccharide interacti ons are now available for this bacteriophage lytic transglycosylase. Examin ation of the active site furthermore reveals that of the two residues that have been implicated in the reaction mechanism of most other c-type lysozym es (Glu35 and Asp52 in hen egg white lysozyme), only a homologous Glu resid ue is present. The lambda lytic transglycosylase is therefore functionally closely related to the Escherichia coli Slt70 and Slt35 lytic transglycosyl ases and goose egg white lysozyme which also lack the catalytic aspartic ac id.