Structures of biologically active muramyl peptides from peptidoglycan of Streptococcus sanguis

The structures of major muramyl peptides derived from peptidoglycanof the oral pathogen Streptococcus sanguis were determined andthe biological activity of the peptides was tested in vitro onhuman monocytes. The muramyl peptides, produced by muramidasedigestion of the purified peptidoglycan, were separated byreversed‐phase high‐performance liquid chromatography,either in their native form or after reduction with sodiumborohydride. Chemical structures of the peptides were elucidated by acombination of matrix‐assisted laser desorption/ionizationtime‐of‐flight mass spectrometry, amino acid analysis,post‐source decay analysis and Edman sequencing. The studyrevealed two distinct monomers: N ‐acetylglucosaminyl‐ N ‐acetylmuramyl‐Ala‐iGln‐Lys(Ala‐Ala)(1), where the Ala‐Ala is connected to theε‐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 thelysine α‐carboxyl group. Two sets of higher oligomers(di‐, tri‐ and tetramers), relatedstructurally to monomers 1 or 2 were also detected. In theseoligomers, the monomeric subunits are linked together byAla‐Ala‐Ala bridges. The native muramyl peptides primedhuman monocytes in vitro for the increased production of themicrobicidal superoxide radical. © 1998 John Wiley & Sons,Ltd.