Abstract:
Archaea possess a variety of cell wall types, none of them identical to bacterial peptidoglycan (murein). The methanogenic archaea Methanobacteria and Methanopyrus sp. possess cell walls of pseudomurein, a structural analogue of murein with a glycan backbone cross-linked by an L-amino acid peptide.  In this paper we present structures of methanogen pseudomurein peptide ligases (termed pMurE) from Methanothermus fervidus (Mfer762) and Methanothermobacter thermautotrophicus (Mth734) that are structurally most closely related to bacterial MurE peptide ligases. The homology of the archaeal pMurE and bacterial MurE proteins is clear both at the overall topology of the structure and at the level of the individual domains. The presence of pMurE ligases in members of the Methanobacteriales and Methanopyrales, that are structurally related to bacterial MurE ligases, supports the idea that the origins of cell walls in some methanogenic archaea and bacteria are evolutionarily related.