The Amino Acids of the Cell Wall of Mycobacterium tuberculosis var. bovis, Strain BCG: Presence of a Poly(l‐Glutamic Acid)

Abstract

A detailed investigation of the amino acids of cell wall preparations obtained by various methods from the BCG strain is reported. “Non‐peptidoglycan” amino acids represent about 15% of the weight of crude, delipidated cell walls (Table 1); trypsin‐chymotrypsin treated, delipidated cell walls contain mainly the peptidoglycan amino acid alanine, glutamic acid and meso‐2,2′‐diaminopimelic acid, the ratio Ala/A2pm being 1.5 and the ratio Glu/A2pm being 2.3, as compared with the expected values of 2 and 1 for a classical peptidoglycan; there are, however, equal molar amounts of d‐glutamic acid and diaminopimelic acid and the excess of glutamic acid is the l‐form. After enzymatic solubilization of the peptidoglycan by lysozyme or by Myxobacter AL1 enzyme 90% of the peptidoglycan amino acids are found in the soluble part; this has been fractionated on Sephadex G‐50 and in most of the fractions obtained the ratio Glu/A2pm is 1, as expect ed, but the ratio Ala/A2pm is closer to 1 than to 2, indicating some other, not yet defined cross link to diaminopimelic acid. The insoluble residue obtained after lysozyme or Myxobacter AL1 enzyme digestion contains a poly (l‐glutamic acid); partial acid hydrolysis allows the solubilization of various l‐glutamic acid oligopeptides, which have been studied by mass spectrometry, after N‐acetylation and per‐methylation; Fig. 3 shows a partial mass spectrum obtained from a peptide containing 6 or 7 glutamic acid residues, proving the sequence Glu‐Glu‐Glu‐Glu; pyroglutamic acid is observed in all spectra, indicating that at least the N‐terminal glutamic acid residue is in α‐linkage. The intact polymer could not be isolated, but the largest fragment obtained has an average chain length of eleven glutamic acid residues. The presence of l‐glutamic acid polymers seems to be restricted to human and bovine strains of Mycobacteria and to Mycobacterium kansasii. Copyright © 1973, Wiley Blackwell. All rights reserved