Structural characterization of Staphylococcus epidermidispeptidoglycan

Peptidoglycans are a key component of microbial cell wall. They contributes to its rigidity and stability, as well the maintenance of a cell shape. In peptidoglycan, a cross-linked polymer composed of backbone consisting of alternating units of beta-1,4 linked N-acetyl glucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) are branched with peptide stems. The peptide side chains are jointed together directly or via peptide bridges. Whereas the saccharide part shows only low diversity (such as O- or N-acetylation and their derivatives of muramic acid), the peptide part can vary significantly in amino acid composition, sequence, and cross-linking. The basic structure of peptidoglycan is a characteristic of a bacterial strain, even so it reflects changes in bacterial metabolism and life conditions. The peptidoglycan structure of S. epidermidis was elucidated after the action of lysostaphin, autolysin with three enzyme activities (cleaves Gly-Gly, MurNAc-Ala, and GlcNAc-MurNAc bonds). The digested peptidoglycans were analyzed by reverse-phase high-performance liquid chromatography on C18 column using a buffer-methanol gradient. Then, the collected fractions were desalted on the same column and characterized by soft ionization techniques of mass spectrometry (MS). The structural study was allowed by electrospray ion-trap MS using the potential of multistage fragmentation experiments. However, the abundant oligosaccharides derived from peptidoglycan were detected and identified. In spite of the previously reported results, the dominating products of enzymatic treatment led to the cleavage both of amide bond between glycan and peptide part and glycosidic bonds.