Structure of the meso-diaminopimelic acid containing peptidoglycans in Escherichia coli B and Bacillus megaterium KM

The peptide subunit of the peptidoglycan of the envelope of Escherichia coli B has the sequence L-Ala-γ-D-Glu-(L)-meso-diaminopimelic acid-(L)-D-Ala. D-Ala-(D)-meso diaminopimelic acid linkages are involved in the cross-linking between peptide subunits. A major part of the wall peptidoglycan of Bacillus megaterium KM is composed of the same aforementioned peptide subunits and peptide cross-linkages. In this latter case, however, the D-Ala-(D)-meso-diaminopimelic acid linkages are not the only important ones. As previously shown, about 15% of the diaminopimelic acid residues are DD and they seem to be involved in another type of peptide cross-linkage. Streptomyces KM endopeptidase solubilizes the walls of Bacillus megaterium. Although this enzyme is not lytic upon Escherichia coli envelope, it liberates disaccharide peptide monomer from a bis-disaccharide peptide dimer, isolated from the same envelope. This dimer is composed of two β-1,4-N-acetylglucosaminyl-N-acetylmuramyl-L-Ala-γ-D-Glu-(L)-meso-diaminopimelic acid-(L)-D-Ala units, joined by a D-Ala-(D)-meso-diaminopimelic acid linkage.