Abstract
Lytic transglycosylases such as Slt35 from E. coli are enzymes involved in bacterial cell wall remodelling and recycling, which represent potential targets for novel antibacterial agents. Here, we investigated a series of known glycosidase inhibitors for their ability to inhibit Slt35. While glycosidase inhibitors such as 1-deoxynojirimycin, castanospermine, thiamet G and miglitol had no effect, the phenothiazinium dye thionine acetate was found to be a weak inhibitor. IC50 values and binding constants for thionine acetate were similar for Slt35 and the hen egg white lysozyme. Molecular docking simulations suggest that thionine binds to the active site of both Slt35 and lysozyme, although it does not make direct interactions with the side-chain of the catalytic Asp and Glu residues as might be expected based on other inhibitors. Thionine acetate also increased the potency of the beta-lactam antibiotic ampicillin against a laboratory strain of E. coli.
Highlights
Bacterial cells are surrounded by a peptidoglycan sacculus on the outside of the cytoplasmic membrane, which is essential for maintaining cell strength and integrity [1]
N-acetylmuramic acid (NAM) residues linked by β-1,4-glycosidic bonds, cross-linked via peptide side-chains [2]
Vertebrate lysozymes are inhibited by the proteinaceous inhibitor Ivy, which is produced by certain Gram-negative bacteria [16]
Summary
Bacterial cells are surrounded by a peptidoglycan sacculus on the outside of the cytoplasmic membrane, which is essential for maintaining cell strength and integrity [1].Peptidoglycan is composed of glycan strands of repeating N-acetylglucosamine (NAG)and N-acetylmuramic acid (NAM) residues linked by β-1,4-glycosidic bonds, cross-linked via peptide side-chains [2]. Lytic transglycosylases are important peptidoglycan-degrading glycosidases [6,7,8], that catalyse cleavage of the β-1,4-glycosidic bond between NAM and NAG residues. Many bacterial species, including human pathogens such as Bacillus anthracis, Staphylococcus aureus, Neisseria meningitides and Neisseria gonorrhoeae, inhibit the activity of both lysozyme and lytic transglycosylases by acetylation of C-6 hydroxyl moieties of NAM residues in their peptidoglycan [14,15]. This is used to control lytic transglycosylase activity and so prevent autolysis [7]. Vertebrate lysozymes are inhibited by the proteinaceous inhibitor Ivy, which is produced by certain Gram-negative bacteria [16]
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