<p>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 is comprised of a sheet of glycan chains connected by short cross-linking polypeptides. Biosynthesis of peptidoglycan is a multi-step (11-12 steps) process comprising three main stages:</p><p> <ul><li>(1) formation of UDP-N-acetylmuramic acid (UDPMurNAc) from N-acetylglucosamine (GlcNAc).</li><li>(2) addition of a short polypeptide chain to the UDPMurNAc.</li><li>(3) 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.</li></ul> </p><p>Stage two involves four key Mur ligase enzymes: MurC (<db_xref db="EC" dbkey="6.3.2.8"/>) [<cite idref="PUB00035788"/>], MurD (<db_xref db="EC" dbkey="6.3.2.9"/>) [<cite idref="PUB00035789"/>], MurE (<db_xref db="EC" dbkey="6.3.2.13"/>) [<cite idref="PUB00035790"/>] and MurF (<db_xref db="EC" dbkey="6.3.2.10"/>) [<cite idref="PUB00035791"/>]. These four Mur ligases are responsible for the successive additions of L-alanine, D-glutamate, meso-diaminopimelate or L-lysine, and D-alanyl-D-alanine to UDP-N-acetylmuramic acid. All four Mur ligases are topologically similar to one another, even though they display low sequence identity. They are each composed of three domains: an N-terminal Rossmann-fold domain responsible for binding the UDPMurNAc substrate; a central domain (similar to ATP-binding domains of several ATPases and GTPases); and a C-terminal domain (similar to dihydrofolate reductase fold) that appears to be associated with binding the incoming amino acid. The conserved sequence motifs found in the four Mur enzymes also map to other members of the Mur ligase family, including folylpolyglutamate synthetase, cyanophycin synthetase and the capB enzyme from Bacillales [<cite idref="PUB00035792"/>]. </p><p>This entry represents UDP-N-acetylmuramoylalanine-D-glutamate ligase (MurD). MurD catalyses the addition of d-glutamate to the nucleotide precursor UDP-N-acetylmuramoyl-l-alanine. </p>