Lipid II

Lipid II

Lipid II is a critical intermediate in the synthesis of peptidoglycan, a component found in the cell wall of bacteria. It is a bactoprenol-linked peptidoglycan subunit that plays a significant role in bacterial cell wall biosynthesis.

Structure

The structure of Lipid II consists of a bactoprenol molecule, a pentapeptide, and a N-acetylglucosamine (NAG)-N-acetylmuramic acid (NAM) disaccharide. The bactoprenol molecule is a lipid carrier that anchors the molecule in the bacterial cell membrane. The pentapeptide is attached to the NAM sugar, and the NAG-NAM disaccharide forms the backbone of the peptidoglycan.

Function

Lipid II serves as a substrate for the transglycosylation and transpeptidation reactions that occur during the final stages of peptidoglycan synthesis. The transglycosylation reaction extends the peptidoglycan chain by adding new NAG-NAM units from Lipid II. The transpeptidation reaction cross-links the peptide chains to provide strength and rigidity to the cell wall.

Role in Antibiotic Action

Many antibiotics, such as vancomycin and teicoplanin, exert their antibacterial effects by binding to Lipid II. This binding prevents the incorporation of Lipid II into the peptidoglycan layer, thereby inhibiting cell wall synthesis and leading to bacterial cell death.

Lipid II Synthesis

The synthesis of Lipid II is a multi-step process that begins with the formation of UDP-NAM-pentapeptide in the cytoplasm. This molecule is then transferred to a bactoprenol phosphate on the inner face of the cell membrane to form Lipid I. The addition of a NAG unit from UDP-NAG results in the formation of Lipid II.

See Also

• Peptidoglycan
• Bactoprenol
• Vancomycin
• Teicoplanin