A crystal lattice structure in the cell wall of eubacteria formed by the linear chains of two alternating amino sugars (N-acetylglucosamine and N-acetylmuramic acid) that are connected to one another by the crosslinking of short peptide chains attached to N-acetylmuramic acid.
Murein serves a structural role in the cell wall of bacteria, giving structural strength and rigidity. It also serves to counteract osmotic pressure of the cytoplasm. It is involved in binary fission during bacterial cell reproduction. The Archaea have a similar layer called pseudopeptidoglycan.
The alternating sugars in the linear chain are joined by a β-(1,4)-glycosidic bond. On every N-acetylmuramic acid, a short amino acid chain (of 4 to 5 residues) is attached. Hence, cross-linking between amino acids attached to the sugar chain, particularly to N-acetylmuramic acid, a 3D structure that is strong and rigid results.
The sequence of amino acid and the molecular structure vary within species of bacteria. Murein is substantially thicker in Gram-positive bacteria than in Gram-negative bacteria.
Word origin: mur(amic acid) + –ein.
Synonym: mucopeptide, peptidoglycan.
See also: cell wall.