Structural basis of cell wall cleavage by a staphylococcal autolysin

The major autolysins (atl) of staphylococcus epidermidis and s. aureus play an important role in cell separation,and their mutants are also attenuated in virulence. therefore,autolysins represent a promising target for the development of new types of antibiotics. here,we report the high-resolution structure of the catalytically active amidase domain amie (amidase s. epidermidis) from the major autolysin of s. epidermidis. this is the first protein structure with an amidase-like fold from a bacterium with a gram-positive cell wall architecture. amie adopts a globular fold,with several α-helices surrounding a central β-sheet. sequence comparison reveals a cluster of conserved amino acids that define a putative binding site with a buried zinc ion. mutations of key residues in the putative active site result in loss of activity,enabling us to propose a catalytic mechanism. we also identified and synthesized muramyltripeptide,the minimal peptidoglycan fragment that can be used as a substrate by the enzyme. molecular docking and digestion assays with muramyltripeptide derivatives allow us to identify key determinants of ligand binding. this results in a plausible model of interaction of this ligand not only for amie,but also for other pgn-hydrolases that share the same fold. as amie active-site mutations also show a severe growth defect,our findings provide an excellent platform for the design of specific inhibitors that target staphylococcal cell separation and can thereby prevent growth of this pathogen. © 2010 zoll et al.