Peptidoglykanlager

Peptidoglykanlager, also known as the peptidoglycan layer or murein layer, is a rigid, mesh-like component that forms the cell wall of most bacteria. It surrounds the cytoplasmic membrane and, depending on the bacterial group, can be thick and exposed (Gram-positive) or thin and localized between an inner membrane and an outer membrane (Gram-negative). The layer provides mechanical strength and helps protect cells from osmotic lysis, contributing to cell shape and integrity.

The structure consists of long chains of alternating disaccharide units: N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). Each NAM carries a short peptide stem, typically containing L-alanine, D-glutamic acid, a diamino acid such as meso-diaminopimelic acid or lysine, and D-alanine. Cross-links between peptide stems link adjacent glycan strands, forming a three-dimensional lattice. In Gram-positive bacteria the layer is thick and often enriched with teichoic and lipoteichoic acids; in Gram-negative bacteria a thinner layer lies between the inner membrane and an outer membrane, with a periplasmic space containing related enzymes.

Biosynthesis of the peptidoglykanlager proceeds from UDP-NAM-pentapeptide in the cytoplasm to a lipid carrier (bactoprenol), then across the membrane where glycosyltransferases assemble glycan strands and penicillin-binding proteins catalyze peptide cross-links (transpeptidation). Antibiotics such as beta-lactams inhibit transpeptidation, while glycopeptides like vancomycin block elongation by binding the D-Ala-D-Ala terminus. The peptidoglycan layer is a major target for antibiotic action and a key determinant of bacterial viability and immune recognition. Some archaeal or atypical bacteria lack classical peptidoglycan, using alternative cell wall polymers.