PEPTIDOGLYCAN

PEPTIDOGLYCAN

The term peptidoglycan was derived from the peptides and the sugars (glycan) that make a molecule; it is also called ‘Murein’. It is found only in bacterial cell walls, thus, its synthesis can be targeted by antibiotics. Peptidoglycan, the polymer of sugars and amino acids,  is a complex, interwoven network that surrounds the entire bacterial cell.

Peptidoglycan consists of carbohydrate backbone (glycan chain) composed of alternating units of N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) molecules.  Glycan chains are connected by short peptides.Attached to each of the muramic acid molecules are a tetrapeptide consisting of both D- and L- amino acids, the precise composition of which differs between bacteria. Teichoic acid and lipoteichoic acid which are polymers of a sugar alcohol (ribitol or glycerol) are embedded in it.

Special Amino Acids Found in Peptidoglycan Layer:

➧ Diaminopimelic acid: Unique to bacterial cells.
➧ D- alanine: Involved in the cross links between tetrapeptides and in the action of penicillin.

Functions of Peptidoglycan Layer

• It provides rigid support to bacterial cells and maintains the characteristic shape of the cell.
• Allows bacterial cell to withstand media of low osmotic pressure, such as water.

Medical Importance of Peptidoglycan Layer

• Peptidoglycan is a good target for antibacterial drugs.  Eg. Penicillins, cephalosporins etc inhibit transpeptidase reaction which makes cross-links between the two adjacent tetrapeptides.
• Lysozyme enzyme present in human tears, mucus, and saliva cleave peptidoglycan backbone breaking its glycosyl bonds.

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