Pseudopeptidoglycan

Pseudopeptidoglycan, also known as pseudomurein, is a cell wall polymer found in a subset of archaea. It serves a role analogous to bacterial peptidoglycan by providing structural strength and osmotic protection, but its chemical makeup and linkages differ substantially from bacterial walls.

Structure and composition: Pseudomurein is built from repeating sugar units of N-acetylglucosamine (GlcNAc) and N-acetyltalosaminuronic acid (NAT) linked by beta-1,3 glycosidic bonds. The sugar backbone is cross-linked by peptides that often incorporate L-lysine, rather than the D-alanine-containing peptides typical of bacterial peptidoglycan. These features produce a distinct three-dimensional network.

Relation to peptidoglycan: Unlike bacterial peptidoglycan, pseudomurein lacks N-acetylmuramic acid (NAM) and uses a different sugar set and glycosidic linkage. The beta-1,3 bonds and the alternative peptide cross-links render pseudomurein resistant to lysozyme, an enzyme that normally targets the bacterial cell wall, and influence how it responds to certain antibiotics.

Occurrence and significance: Pseudomurein is found in several methanogenic archaea, particularly within certain orders such as Methanobacteriales. It contributes to cell wall integrity in organisms inhabiting extreme environments and affects susceptibility to antimicrobial agents that target peptidoglycan synthesis in bacteria.

Notes: The term pseudopeptidoglycan reflects both its functional similarity to peptidoglycan and its distinct chemical composition. The study of pseudomurein helps illuminate the diversity of cell wall architectures across the domains of life.