Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer (sacculus) that surrounds the bacterial cytoplasmic membrane. The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). Attached to the N-acetylmuramic acid is an oligopeptide chain made of three to five amino acids. The peptide chain can be cross-linked to the peptide chain of another strand forming the 3D mesh-like layer. Peptidoglycan serves a structural role in the bacterial cell wall, giving structural strength, as well as counteracting the osmotic pressure of the cytoplasm. This repetitive linking results in a dense peptidoglycan layer which is critical for maintaining cell form and withstanding high osmotic pressures, and it is regularly replaced by peptidoglycan production. Peptidoglycan hydrolysis and synthesis are two processes that must occur in order for cells to grow and multiply, a technique carried out in three stages: clipping of current material, insertion of new material, and re-crosslinking of existing material to new material.
In enzymology, a D-aspartate ligase is an enzyme that catalyzes the chemical reaction
In enzymology, a UDP-N-acetylmuramate—L-alanine ligase is an enzyme that catalyzes the chemical reaction
In enzymology, a UDP-N-acetylmuramoyl-L-alanine—D-glutamate ligase is an enzyme that catalyzes the chemical reaction
In enzymology, a UDP-N-acetylmuramoyl-L-alanyl-D-glutamate—L-lysine ligase is an enzyme that catalyzes the chemical reaction
In enzymology, a UDP-N-acetylmuramoyl-tripeptide—D-alanyl-D-alanine ligase is an enzyme that catalyzes the chemical reaction
In enzymology, an UDP-N-acetylmuramoylpentapeptide-lysine N6-alanyltransferase (EC 2.3.2.10) is an enzyme that catalyzes the chemical reaction
Peptidoglycan glycosyltransferase is an enzyme used in the biosynthesis of peptidoglycan. It transfers a disaccharide-peptide from a donor substrate to synthesize a glycan chain.
In enzymology, an undecaprenyldiphospho-muramoylpentapeptide beta-N-acetylglucosaminyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, an UDP-N-acetylglucosamine—lysosomal-enzyme N-acetylglucosaminephosphotransferase is an enzyme that catalyzes the chemical reaction
In enzymology, an undecaprenol kinase is an enzyme that catalyzes the chemical reaction
In enzymology, an undecaprenyl-phosphate galactose phosphotransferase is an enzyme that catalyzes the chemical reaction
The bacterial cell wall provides strength and rigidity to counteract internal osmotic pressure, and protection against the environment. The peptidoglycan layer gives the cell wall its strength, and helps maintain the overall shape of the cell. The basic peptidoglycan structure of both Gram-positive and Gram-negative bacteria comprises a sheet of glycan chains connected by short cross-linking polypeptides. Biosynthesis of peptidoglycan is a multi-step process comprising three main stages:
- formation of UDP-N-acetylmuramic acid (UDPMurNAc) from N-acetylglucosamine (GlcNAc).
- addition of a short polypeptide chain to the UDPMurNAc.
- addition of a second GlcNAc to the disaccharide-pentapeptide building block and transport of this unit through the cytoplasmic membrane and incorporation into the growing peptidoglycan layer.
Undecaprenyl-phosphate glucose phosphotransferase is an enzyme with systematic name UDP-glucose:ditrans,octacis-undecaprenyl-phosphate glucose phosphotransferase. This enzyme catalyses the following chemical reaction
UDP-N-acetylglucosamine—undecaprenyl-phosphate N-acetylglucosaminephosphotransferase is an enzyme with systematic name UDP-N-acetyl-alpha-D-glucosamine:ditrans,octacis-undecaprenyl phosphate N-acetyl-alpha-D-glucosaminephosphotransferase. This enzyme catalyses the following chemical reaction
UDP-N-acetylglucosamine---decaprenyl-phosphate N-acetylglucosaminephosphotransferase is an enzyme with systematic name UDP-N-acetyl-alpha-D-glucosamine:trans,octacis-decaprenyl-phosphate N-acetylglucosaminephosphotransferase. This enzyme catalyses the following chemical reaction
UDP-N-acetylmuramoyl-L-alanyl-D-glutamate—2,6-diaminopimelate ligase is an enzyme with systematic name UDP-N-acetylmuramoyl-L-alanyl-D-glutamate:meso-2,6-diaminoheptanedioate gamma-ligase (ADP-forming). This enzyme catalyses the following chemical reaction
UDP-N-acetylmuramoyl-L-alanyl-D-glutamate—D-lysine ligase is an enzyme with systematic name UDP-N-acetylmuramoyl-L-alanyl-D-glutamate:D-lysine alpha-ligase (ADP-forming). This enzyme catalyses the following chemical reaction
Lipid II is a precursor molecule in the synthesis of the cell wall of bacteria. It is a peptidoglycan, which is amphipathic and named for its bactoprenol hydrocarbon chain, which acts as a lipid anchor, embedding itself in the bacterial cell membrane. Lipid II must translocate across the cell membrane to deliver and incorporate its disaccharide-pentapeptide "building block" into the peptidoglycan mesh. Lipid II is the target of several antibiotics.
Undecaprenyl phosphate (UP), also known lipid-P, bactoprenol and C55-P., is a molecule with the primary function of trafficking polysaccharides across the cell membrane, largely contributing to the overall structure of the cell wall in Gram-positive bacteria. In some situations, UP can also be utilized to carry other cell-wall polysaccharides, but UP is the designated lipid carrier for peptidoglycan. During the process of carrying the peptidoglycan across the cell membrane, N-acetylglucosamine and N-acetylmuramic acid are linked to UP on the cytoplasmic side of the membrane before being carried across. UP works in a cycle of phosphorylation and dephosphorylation as the lipid carrier gets used, recycled, and reacts with undecaprenyl phosphate. This type of synthesis is referred to as de novo synthesis where a complex molecule is created from simpler molecules as opposed to a complete recycle of the entire structure.
