Abstract
Cells of eukaryotic or prokaryotic origin express proteins with LysM domains that associate with the cell wall envelope of bacteria. The molecular properties that enable LysM domains to interact with microbial cell walls are not yet established. Staphylococcus aureus, a spherical microbe, secretes two murein hydrolases with LysM domains, Sle1 and LytN. We show here that the LysM domains of Sle1 and LytN direct murein hydrolases to the staphylococcal envelope in the vicinity of the cross-wall, the mid-cell compartment for peptidoglycan synthesis. LysM domains associate with the repeating disaccharide β-N-acetylmuramic acid, (1→4)-β-N-acetylglucosamine of staphylococcal peptidoglycan. Modification of N-acetylmuramic acid with wall teichoic acid, a ribitol-phosphate polymer tethered to murein linkage units, prevents the LysM domain from binding to peptidoglycan. The localization of LytN and Sle1 to the cross-wall is abolished in staphylococcal tagO mutants, which are defective for wall teichoic acid synthesis. We propose a model whereby the LysM domain ensures septal localization of LytN and Sle1 followed by processive cleavage of peptidoglycan, thereby exposing new LysM binding sites in the cross-wall and separating bacterial cells.
Highlights
Staphylococcus aureus secretes murein hydrolases with LysM domains
D, purified mCherry, LytN-mCherry, LytN⌬LysM-mCherry, or LytN⌬CHAP-mCherry was incubated with purified peptidoglycan from S. aureus Newman, which had been isolated by glass bead disruption of murein sacculi, treated with protease, and extracted with detergent, and Wall teichoic acid (WTA) was removed with hydrofluoric acid (HF)
The unique spherical architecture of the staphylococcal cell wall is achieved through a replication mechanism whereby peptidoglycan synthesis occurs in the cross-wall [24], a membraneenclosed compartment into which cell wall synthesis enzymes, lipid II, and YSIRK(G/S) signal peptide-bearing precursor proteins are being trafficked [36, 54]
Summary
Results: We show here that the LysM domains bind to the cross-wall, the mid-cell compartment for peptidoglycan synthesis, through association with its repeating disaccharide. We show here that the LysM domains of Sle and LytN direct murein hydrolases to the staphylococcal envelope in the vicinity of the crosswall, the mid-cell compartment for peptidoglycan synthesis. We propose a model whereby the LysM domain ensures septal localization of LytN and Sle followed by processive cleavage of peptidoglycan, thereby exposing new LysM binding sites in the cross-wall and separating bacterial cells. Wall teichoic acid (WTA) is a key determinant of Atl localization; in a tagO mutant, defective in the synthesis of the murein linkage units for polyribitol-phosphate WTA [33], Atl localization is not restricted to the cross-wall sections of the staphylococcal envelope and instead binds uniformly to the cell surface [34]. We investigated the role of the LysM domains in Sle and LytN during cross-wall splitting and cell separation of S. aureus
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