3HDS: Crystal Structure Of 4-methylmuconolactone Methylisomerase In Complex With Mes

When methyl-substituted aromatic compounds are degraded via ortho (intradiol)-cleavage of 4-methylcatechol, the dead-end metabolite 4-methylmuconolactone (4-ML) is formed. Degradation of 4-ML has only been described in few bacterial species, including Pseudomonas reinekei MT1. The isomerization of 4-ML to 3-methylmuconolactone (3-ML) is the first step required for the mineralization of 4-ML and is catalyzed by an enzyme termed 4-methylmuconolactone methylisomerase (MLMI). We identified the gene encoding MLMI in P. reinekei MT1 and solved the crystal structures of MLMI in complex with 3-ML at 1.4-A resolution, with 4-ML at 1.9-A resolution and with a MES buffer molecule at 1.45-A resolution. MLMI exhibits a ferredoxin-like fold and assembles as a tight functional homodimeric complex. We were able to assign the active site clefts of MLMI from P. reinekei MT1 and of the homologous MLMI from Cupriavidus necator JMP134, which has previously been crystallized in a structural genomics project. Kinetic and structural analysis of wild-type MLMI and variants created by site-directed mutagenesis indicate Tyr-39 and His-26 to be the most probable catalytic residues. The previously proposed involvement of Cys-67 in covalent catalysis can now be excluded. Residue His-52 was found to be important for substrate affinity, with only marginal effect on catalytic activity. Based on these results, a novel catalytic mechanism for the isomerization of 4-ML to 3-ML by MLMI, involving a bislactonic intermediate, is proposed. This broadens the knowledge about the diverse group of proteins exhibiting a ferredoxin-like fold.
PDB ID: 3HDSDownload
MMDB ID: 77027
PDB Deposition Date: 2009/5/7
Updated in MMDB: 2009/09
Experimental Method:
x-ray diffraction
Resolution: 1.45  Å
Source Organism:
Pseudomonas reinekei
Similar Structures:
Biological Unit for 3HDS: trimeric; determined by author and by software (PISA)
Molecular Components in 3HDS
Label Count Molecule
Proteins (3 molecules)
4-methylmuconolactone Methylisomerase
Molecule annotation
Short Peptide Aswsa
Molecule annotation
Chemicals (2 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB