Extended Data Fig. 2. Muropeptide analysis identifies a tetrasaccharide-monopeptide.

a, Schematic of sacculi isolation and mutanolysin/NaBH₄ treatment to generate muropeptides for LC-MS analysis. b, Total ion chromatograms comparing the muropeptide species isolated from WT vs. ∆lytH sacculi. Muropeptide species eluted between 12–18 min using this analytical method. The XCMS online platform was used to identify species that were enriched or depleted between the two strains. c, The tetrasaccharide-monopeptide species was enriched in sacculi isolated from cells expressing lytH^WT. A chemical structure consistent with this species, based on an [M]⁺² ion with experimental m/z = 866.3881, is shown. d, The [M]⁺² ion was targeted for fragmentation to confirm the species was a tetrasaccharide-monopeptide. e, The theoretical and experimental isotope distributions for the tetrasaccharide-monopeptide species are shown.