UDP-N-acetylmuramate---L-alanine ligase

 

UDP-N-acetylmuramate-alanine ligase (MurC) is an essential, cytoplasmic peptidoglycan biosynthetic enzyme that catalyses the ATP-dependent ligation of L-alanine (Ala) and UDP-N-acetylmuramic acid (UNAM) to form UDP-N-acetylmuramyl-L-alanine (UNAM-Ala). This reaction is part of the biosynthesis of cell walls in bacteria. MurC is a nonribosomal peptide ligase which utilises ATP to form an amide bond between L-alanine and UNAM. Mechanistic studies on the Escherichia coli enzyme demonstrated that the enzyme-catalysed reaction proceeds through an acyl phosphate UNAM intermediate prior to L-alanine addition.

 

Reference Protein and Structure

Sequence
P45066 UniProt (6.3.2.8) IPR005758 (Sequence Homologues) (PDB Homologues)
Biological species
Haemophilus influenzae Rd KW20 (Bacteria) Uniprot
PDB
1p3d - Crystal Structure of UDP-N-acetylmuramic acid:L-alanine ligase (MurC) in Complex with UMA and ANP. (1.7 Å) PDBe PDBsum 1p3d
Catalytic CATH Domains
3.40.1190.10 CATHdb (see all for 1p3d)
Cofactors
Magnesium(2+) (1)
Click To Show Structure

Enzyme Reaction (EC:6.3.2.8)

ATP(4-)
CHEBI:30616ChEBI
+
L-alanine zwitterion
CHEBI:57972ChEBI
+
UDP-N-acetyl-alpha-D-muramate(3-)
CHEBI:70757ChEBI
→
hydrogenphosphate
CHEBI:43474ChEBI
+
UDP-N-acetyl-alpha-D-muramoyl-L-alaninate(3-)
CHEBI:83898ChEBI
+
ADP(3-)
CHEBI:456216ChEBI
+
hydron
CHEBI:15378ChEBI
Alternative enzyme names: L-Ala ligase, L-alanine-adding enzyme, MurC synthetase, UDP-N-acetylmuramoyl-L-alanine synthetase, UDP-N-acetylmuramoylalanine synthetase, UDP-N-acetylmuramyl:L-alanine ligase, UDP-MurNAc:L-alanine ligase, UDP-acetylmuramyl-L-alanine synthetase, UDPMurNAc-L-alanine synthetase, Alanine-adding enzyme, Uridine 5'-diphosphate-N-acetylmuramyl-L-alanine synthetase, Uridine diphosphate N-acetylmuramate:L-alanine ligase, Uridine diphospho-N-acetylmuramoylalanine synthetase, Uridine-diphosphate-N-acetylmuramate:L-alanine ligase, UDP-N-acetylmuramate:L-alanine ligase (ADP-forming),

Enzyme Mechanism

Introduction

An acyl-phosphate intermediate is formed via transfer of the γ-phosphate of ATP to the carboxylate of UNAM or the C-terminal carboxylate of UNAM peptide. The amide of the incoming amino acid displaces the phosphate by nucleophilic attack, thereby extending the peptide chain.

Catalytic Residues Roles

UniProt PDB* (1p3d)
Thr130, Glu173 Thr130A, Glu173A Forms part of the divalent metal ion binding site. metal ligand
Lys129 Lys129A Part of a well conserved ATP binding motif, helps stabilise the reactive intermediates and transition states formed during the course of the reaction. The side chain N-eta of Lys 129 contacts a gamma-phosphate oxygen. electrostatic stabiliser
*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file; y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain; C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.

Chemical Components

References

  1. Mol CD et al. (2003), J Bacteriol, 185, 4152-4162. Crystal Structures of Active Fully Assembled Substrate- and Product-Bound Complexes of UDP-N-Acetylmuramic Acid:L-Alanine Ligase (MurC) from Haemophilus influenzae. DOI:10.1128/jb.185.14.4152-4162.2003. PMID:12837790.
  2. Deva T et al. (2006), Acta Crystallogr D Biol Crystallogr, 62, 1466-1474. Structure of Escherichia coli UDP-N-acetylmuramoyl:L-alanine ligase (MurC). DOI:10.1107/S0907444906038376. PMID:17139082.
  3. Marmor S et al. (2001), Biochemistry, 40, 12207-12214. Biochemical Characterization of a Phosphinate Inhibitor ofEscherichia coliMurC. DOI:10.1021/bi015567m.
  4. Bouhss A et al. (1997), Biochemistry, 36, 11556-11563. Invariant Amino Acids in the Mur Peptide Synthetases of Bacterial Peptidoglycan Synthesis and Their Modification by Site-Directed Mutagenesis in the UDP-MurNAc:l-Alanine Ligase fromEscherichiacoli†. DOI:10.1021/bi970797f. PMID:9305945.
  5. Falk PJ et al. (1996), Biochemistry, 35, 1417-1422. Biochemical evidence for the formation of a covalent acyl-phosphate linkage between UDP-N-acetylmuramate and ATP in the Escherichia coli UDP-N-acetylmuramate:L-alanine ligase-catalyzed reaction. DOI:10.1021/bi952078b. PMID:8634271.

Step 1.

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Catalytic Residues Roles

Residue Roles
Lys129A electrostatic stabiliser
Glu173A metal ligand
Thr130A metal ligand

Chemical Components

Step 1.

Contributors

Alex Gutteridge, Craig Porter, Gemma L. Holliday