Abstract
After bacterial cell division, the daughter cells are still covalently interlinked by the peptidoglycan network which is resolved by specific hydrolases (autolysins) to release the daughter cells. In staphylococci, the major autolysin (Atl) with its two domain enzymes, N-acetylmuramyl-L-alanine amidase (AmiA) and β-N-acetylglucosaminidase (GlcA), resolves the peptidoglycan to release the daughter cells. Internal deletions in each of the enzyme domains revealed defined morphological alterations such as cell cluster formation in ΔamiA, ΔglcA and Δatl, and asymmetric cell division in the ΔglcA. A most important finding was that GlcA activity requires the prior removal of the stem peptide by AmiA for its activity thus the naked glycan strand is its substrate. Furthermore, GlcA is not an endo-β-N-acetylglucosaminidase but an exo-enzyme that cuts the glycan backbone to disaccharides independent of its O-acetylation modification. Our results shed new light into the sequential peptidoglycan hydrolysis by AmiA and GlcA during cell division in staphylococci.
Highlights
After bacterial cell division, the daughter cells are still covalently interlinked by the peptidoglycan network which is resolved by specific hydrolases to release the daughter cells
The staphylococcal major autolysin, Atl, is a multidomain protein composed of the signal peptide (SP), the propeptide (PP), the catalytic domain of the amidase AmiA followed by the repeat domains R1 and R2, and the glucosaminidase domain (GlcA) which is preceded by the R3 repeat domain (Fig. 1a)
Comparative scanning electron microscopic (SEM) analysis of SA113 and the mutants ΔamiA, ΔglcA and Δatl grew to midexponential phase revealed that in all mutants, the cell separation was affected as manifested by increased cell cluster formation, indicating that both, AmiA and GlcA contribute to cell separation
Summary
The daughter cells are still covalently interlinked by the peptidoglycan network which is resolved by specific hydrolases (autolysins) to release the daughter cells. The major autolysin (Atl) with its two domain enzymes, Nacetylmuramyl-L-alanine amidase (AmiA) and β-N-acetylglucosaminidase (GlcA), resolves the peptidoglycan to release the daughter cells. This is a secreted bifunctional multidomain enzyme typical for the genera Staphylococcus and Macrococcus[3] Atl of both S. aureus and S. epidermidis is processed into two bacteriolytic active domains, the ≈62 kDa Nacetylmuramyl-L-alanine amidase (AmiA) and the ≈51 kDa endo-beta-N-acetylglucosaminidase (GlcA)[4,5,6]. Deletion of the entire atl gene in S. epidermidis led to huge cell cluster formation indicating that daughter cell separation was severely affected and the supernatants lacked five prominent proteins[4] This defect could largely be complemented by atl or amiA alone. This processing occurs in such a way that each of the enzymes is supplied with repeat domains generating AmiA-R1ab/
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