The Murein-Lipoprotein Linkage in the Cell Wall of Escherichia coli

After digestion of the murein-lipoprotein complex (rigid layer) of the E. coli cell wall with lysozyme the solubilized lipoprotein contained 2 disaccharide units of the murein per 1 lipoprotein molecule. From purely enzymatic degradation of the murein-lipoprotein complex with pronase and lysozyme the peptide GlcNAc-MurNAc-l-Ala-d-Glu-Dpm-Lys-Arg was isolated, where MurNAc =N-acetyl-muramic acid and Dpm =meso-2,6-diaminopimelic acid. The missing d-alanine in this repeating unit of the murein is replaced by the lysyl-arginine dipeptide of the lipoprotein. The lipoprotein molecules are therefore linked to the carboxyl group of the optical l-center of the diaminopimelic acid of the murein.