Peptidoglycan - Structure

Structure

The peptidoglycan layer in the bacterial cell wall is a crystal lattice structure formed from linear chains of two alternating amino sugars, namely N-acetylglucosamine (GlcNAc or NAG) and N-acetylmuramic acid (MurNAc or NAM). The alternating sugars are connected by a β-(1,4)-glycosidic bond. Each MurNAc is attached to a short (4- to 5-residue) amino acid chain, containing -alanine, -glutamic acid, meso-diaminopimelic acid, and -alanine in the case of Escherichia coli (a Gram-negative bacteria) or -alanine, -glutamine, -lysine, and -alanine with a 5-glycine interbridge between tetrapeptides in the case of Staphylococcus aureus (a Gram-positive bacteria). These amino acids, except the -amino acids, do not occur in proteins and are thought to help protect against attacks by most peptidases.

Cross-linking between amino acids in different linear amino sugar chains occurs with the help of the enzyme transpeptidase and results in a 3-dimensional structure that is strong and rigid. The specific amino acid sequence and molecular structure vary with the bacterial species.

  • The structure of peptidoglycan.

  • Gram-positive cell wall

  • Penicillin binding protein forming cross-links in newly formed bacterial cell wall.

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