REPLACEMENT OF DIAMINOPIMELIC ACID BY CYSTATHIONINE OR LANTHIONINE IN THE PEPTIDOGLYCAN OF ESCHERICHIA-COLI

In Escherichia coli, auxotrophy for diaminopimelic acid (A(2)pm) can be suppressed by growth with exogenous cystathionine or lanthionine. The incorporation of cystathionine into peptidoglycan metabolism was examined with a dapA metC mutant, whereas for lanthionine, a dnpA metA mutant strain was used. Analysis of peptidoglycan precursors and sacculi isolated from cells grown with epimeric cystathionine or lanthionine showed that meso-A(2)pm was totally replaced in the same position by either sulfur containing amino acid. Moreover, mainly L-allo-cystathionine (95%) or meso-lanthionine (93%) was incorporated into the precursors and sacculi. For this purpose, a new, efficient high-pressure liquid chromatography (HPLC) technique for analysis of the cystathionine isomers was developed. The formation of the UDP-MurNAc tripeptide appeared to be a critical step, since the MurE synthetase accepted meso-lanthionine or D-allo- or L-allo-cystathionine in vitro as good substrates, although with higher K-m values. Presumably, the 10-fold-higher UDP-MurNAc-L-LAla-D-Glu pool of cells grown with cystathionine or lanthionine ensured a normal rate of synthesis. The kinetic parameters of the MurF synthetase catalyzing the addition of D-alanyl-D-alanine were very similar for the meso-A(2)pm-, L-allo-cystathione-, and meso-lanthionine-containing UDP-MurNAc tripeptides. HPLC analysis of the soluble fragments resulting from 95% digestion by Chalaropsis N-acetylmuramidase of the peptidoglycan material in isolated sacculi revealed that the proportion of the main dimer was far lower in cystathione and lanthionine sacculi.