Peptidoglycan precursor Lipid II and Penicillin-Binding Proteins (Lipid II/PBP)

Peptidoglycan precursor Lipid II is a vital, membrane-anchored molecule essential for the construction of the bacterial cell wall. It consists of a C55-isoprenoid (bactoprenol) carrier linked via a pyrophosphate group to a disaccharide-pentapeptide unit. Lipid II is transported across the cytoplasmic membrane, where it serves as the substrate for transglycosylases that polymerize the glycan chains and transpeptidases (known as Penicillin-Binding Proteins or PBPs) that cross-link the peptide stems to form a robust peptidoglycan network [1, 2]. This machinery is the primary target for many of the most clinically significant antibiotics. Glycopeptides, such as vancomycin, bind to the D-alanyl-D-alanine terminus of the Lipid II pentapeptide, physically blocking the enzymatic actions of transglycosylases and transpeptidases [3]. Beta-lactam antibiotics, including penicillins and cephalosporins, act as structural analogs of the D-Ala-D-Ala substrate and covalently inhibit PBPs, preventing the cross-linking necessary for cell wall stability [2, 4]. Because this machinery is unique to bacteria and absent in human cells, it remains a highly effective and selective target for treating a wide range of bacterial infections, although the emergence of resistance mechanisms like modified Lipid II (D-Ala-D-Lac) or altered PBPs poses a significant therapeutic challenge [1, 5]. [1] Breukink E, de Kruijff B. Lipid II as a target for antibiotics. Nat Rev Drug Discov. 2006;5(4):321-332. [2] Sauvage E, et al. The penicillin-binding proteins: structure and role in peptidoglycan biosynthesis. FEMS Microbiol Rev. 2008;32(2):234-258. [3] Kahne D, et al. Glycopeptide and lipoglycopeptide antibiotics. Chem Rev. 2005;105(2):425-448. [4] Tipper DJ, Strominger JL. Mechanism of action of penicillins. Proc Natl Acad Sci U S A. 1965;54(4):1133-1141. [5] Courvalin P. Vancomycin resistance in Gram-positive cocci. Clin Infect Dis. 2006;42 Suppl 1:S25-34.

Other names

Lipid IIUndecaprenyl-pyrophosphoryl-MurNAc-pentapeptide-GlcNAcPenicillin-Binding ProteinsPBPsTransglycosylaseTranspeptidaseCell wall synthesis machineryPeptidoglycan biosynthesis pathway

Inhibition of bacterial cell wall synthesis by binding to the D-Ala-D-Ala terminus of Lipid II (preventing polymerization and cross-linking) or by covalently inhibiting the transpeptidase activity of Penicillin-Binding Proteins (PBPs).