Biosynthesis of pseudomurein: isolation of putative precursors from Methanobacterium thermoautotrophicum.

In aqueous trichloroacetic acid extracts of Methanobacterium thermoautotrophicum the following compounds, which are supposed to be precursors in the biosynthesis of the glycan strand of the pseudomurein, were isolated and identified: (i) a disaccharide (compound II) composed of uridine 5'-diphosphate, N-acetylglucosamine and N-acetyltalosaminuronic acid with N-acetylglucosamine at the reducing end, (ii) uridine 5'-diphospho-N-acetylglucosamine, and (iii) uridine 5'-diphospho-N-acetylgalactosamine. However, the corresponding monomeric derivative of N-acetyltalosaminuronic acid could not be detected. It is assumed that N-acetyltalosaminuronic acid may be formed from N-acetylgalactosamine by epimerisation and oxidation at the disaccharide level. These findings indicate that the biosynthetic pathways of murein and pseudomurein are quite different.