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The structures of major muramyl peptides derived from peptidoglycan of the oral pathogen Streptococcus sanguis were determined and the biological activity of the peptides was tested in vitro on human monocytes. The muramyl peptides, produced by muramidase digestion of the purified peptidoglycan, were separated by reversed-phase high-performance liquid chromatography, either in their native form or after reduction with sodium borohydride. Chemical structures of the peptides were elucidated by a combination of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, amino acid analysis, post-source decay analysis and Edman sequencing. The study revealed two distinct monomers: N-acetylglucosaminyl-N-acetylmuramyl-Ala-iGln-Lys(Ala-Ala) (1), where the Ala-Ala is connected to the epsilon-amino group of lysine, and N-acetylglucosaminyl-N-acetylmuramyl-Ala-iGln-Lys(Ala-Ala)-Ala-Ala (2), where an additional dialanyl residue is attached to the lysine alpha-carboxyl group. Two sets of higher oligomers (di-, tri- and tetramers), related structurally to monomers 1 or 2 were also detected. In these oligomers, the monomeric subunits are linked together by Ala-Ala-Ala bridges. The native muramyl peptides primed human monocytes in vitro for the increased production of the microbicidal superoxide radical.

A polysaccharide was found to be covalently linked to the peptidoglycan of the unicellular cyanobacterium Synechocystis sp. strain PCC6714 via phosphodiester bonds. It could be cleaved from the peptidoglycan-polysaccharide (PG-PS) complex by hydrofluoric acid (HF) treatment in the cold (48% HF, 0 degrees C, 48 h) yielding a pure, HF-insoluble peptidoglycan fraction and an HF-soluble polysaccharide fraction. The PG-PS complex was isolated from the Triton X-100-insoluble cell wall fraction by hot sodium dodecyl sulfate treatment and digestion with proteases. Digestion of the complex with N-acetylmuramidase released the glycopeptide-linked polysaccharide, which was further purified by dialysis and gel filtration on Sephadex G-50 and G-200. The polysaccharide consisted of glucosamine, mannosamine, galactosamine, mannose, and glucose and had a molecular weight of 25,000 to 30,000. Muramic acid-6-phosphate was identified as the binding site of the covalently linked, nonphosphorylated polysaccharide as revealed by chemical analysis of linkage fragments of the PG-PS complex.