Which polysaccharide is found in the archaeal cell wall instead of peptidoglycan?
Bacterial cell walls are built on peptidoglycan, a heteropolymer of N-acetylglucosamine and N-acetylmuramic acid crosslinked by peptide bridges sensitive to lysozyme and penicillin. Archaea do not synthesize peptidoglycan; instead, methanogenic euryarchaeota that possess a rigid wall produce pseudomurein, also called pseudopeptidoglycan, which superficially resembles peptidoglycan but differs chemically enough to confer resistance to classical wall antibiotics. Pseudomurein consists of N-acetylglucosamine linked to N-acetyltalosaminuronic acid rather than N-acetylmuramic acid, bearing L-amino acids at crosslink positions rather than D-amino acids typical of bacteria, and featuring beta-1,3 glycosidic linkages in place of beta-1,4. Teichoic acid is unique to Gram-positive walls, chitin is polymer of N-acetylglucosamine found in fungi and arthropods, not in archaea. Thus presence of pseudomurein instead of true murein defines wall chemistry in certain methanogens and explains why lysozyme and beta-lactams fail to lyse these organisms despite similar morphology. Genomic analysis shows pseudomurein biosynthetic enzymes are unrelated to bacterial Mur ligases, suggesting independent evolutionary origin, and presence of NAT instead of NAM impacts innate immune recognition because mammalian peptidoglycan recognition proteins like PGRP and NOD receptors fail to detect archaeal wall, contributing to commensal tolerance in gut methanogens.
Ref: Albers & Meyer, Nature Rev Microbiol 2011, Pseudomurein; Kandler & Konig, Archaea 1998, Cell Walls.