Peptidoglycan is a net-like polymer which surrounds the cytoplasmic membrane of most bacteria and functions to maintain cell shape and prevent rupture due to the internal turgor. In E. coli K-12, the peptidoglycan consists of glycan strands of alternating subunits of N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) which are cross-linked by short peptides. The pathway for constructing this net involves two cell compartments: cytoplasm and periplasmic space. The pathway starts with a beta-D-fructofuranose going through a mannose PTS permease, phosphorylating the compound and producing a beta-D-fructofuranose 6 phosphate. This compound can be obtained from the glycolysis and pyruvate dehydrogenase or from an isomerization reaction of Beta-D-glucose 6-phosphate through a glucose-6-phosphate isomerase. The compound Beta-D-fructofuranose 6 phosphate and L-Glutamine react with a glucosamine fructose-6-phosphate aminotransferase, thus producing a glucosamine 6-phosphate and a l-glutamic acid. The glucosamine 6-phosphate interacts with phosphoglucosamine mutase in a reversible reaction producing glucosamine-1P. Glucosamine-1p and acetyl-CoA undergo acetylation through a bifunctional protein glmU releasing Coa and a hydrogen ion and producing a N-acetyl-glucosamine 1-phosphate. Glmu, being a bifunctional protein catalyzes the interaction of N-acetyl-glucosamine 1-phosphate, hydrogen ion and UTP into UDP-N-acetylglucosamine and pyrophosphate. UDP-N-acetylglucosamine then interacts with phosphoenolpyruvic acid and a UDP-N acetylglucosamine 1- carboxyvinyltransferase releasing a phosphate and the compound UDP-N-acetyl-alpha-D-glucosamine-enolpyruvate. The latter undergoes a NADPH dependent reduction producing a UDP-N-acetyl-alpha-D-muramate catalyzed by a UDP-N-acetylenolpyruvoylglucosamine reductase. UDP-N-acetyl-alpha-D-muramate and L-alanine react in an ATP-mediated ligation through a UDP-N-acetylmuramate-alanine ligase releasing an ADP, hydrogen ion, phosphate and a UDP-N-acetylmuramoyl-L-alanine. Next, UDP-N-acetylmuramoylalanine-D-glutamate ligase catalyzes an ATP, D-glutamic acid and UDP-N-acetylmuramoyl-L-alanine releasing ADP, phosphate and UDP-N-acetylmuramoyl-L-alanyl-D-glutamate. The latter product then interacts with meso-diaminopimelate in an ATP mediated ligation through a UDP-N-acetylmuramoylalanine-D-glutamate-2,6-diaminopimelate ligase resulting in ADP, phosphate, hydrogen ion and UDP-N-Acetylmuramoyl-L-alanyl-D-gamma-glutamyl-meso-2,6-diaminopimelate. This compound in turn with D-alanyl-D-alanine react in an ATP-mediated ligation through UDP-N-Acetylmuramoyl-tripeptide-D-alanyl-D-alanine ligase to produce UDP-N-acetyl-alpha-D-muramoyl-L-alanyl-gama-D-glutamyl-meso-2,6-diaminopimeloyl-Dalanyl-D-alanine and hydrogen ion, ADP, phosphate. UDP-N-acetyl-alpha-D-muramoyl-L-alanyl-gama-D-glutamyl-meso-2,6-diaminopimeloyl-Dalanyl-D-alanine interacts with di-trans,octa-cis-undecaprenyl phosphate through a phospho-N-acetylmuramoyl-pentapeptide-transferase, resulting in UMP and Undecaprenyl-diphospho-N-acetylmuramoyl-L-alanyl-D-glutamyl-meso-2,6-diaminopimeloyl-D-alanyl-D-alanine which in turn reacts with a UDP-N-acetylglucosamine through a N-acetylglucosaminyl transferase to produce a hydrogen, UDP and ditrans,octacis-undecaprenyldiphospho-N-acetyl-(N-acetylglucosaminyl)muramoyl-L-alanyl-gamma-D-glutamyl-meso-2,6-diaminopimeloyl-D-alanyl-D-alanine. This compound ends the cytoplasmic part of the pathway. ditrans,octacis-undecaprenyldiphospho-N-acetyl-(N-acetylglucosaminyl)muramoyl-L-alanyl-gamma-D-glutamyl-meso-2,6-diaminopimeloyl-D-alanyl-D-alanine is transported through a lipi II flippase. Once in the periplasmic space, the compound reacts with a penicillin binding protein 1A prodducing a peptidoglycan dimer, a hydrogen ion, and UDP. The peptidoglycan dimer then reacts with a penicillin binding protein 1B producing a peptidoglycan with D,D, cross-links and a D-alanine.

Peptidoglycan Biosynthesis I References