Structure of the 2,4'-dihydroxyacetophenone dioxygenase from Alcaligenes sp. 4HAP

Area of Science:

• Biochemistry
• Enzymology
• Structural Biology

Background:

• 2,4 andomIndex'-dihydroxyacetophenone dioxygenase (DAD) is an unusual enzyme catalyzing C-C bond cleavage in a substituent.
• DAD belongs to the cupin superfamily and contains non-heme iron.
• The enzyme is a homotetramer composed of 20.3 kDa subunits.

Purpose of the Study:

• To determine the first X-ray structure of the DAD enzyme from Alcaligenes sp. 4HAP.
• To elucidate the structural basis for DAD's unique catalytic mechanism.

Main Methods:

• X-ray crystallography at 2.2 Å resolution.
• Protein structure determination and analysis.
• Molecular modeling of substrate binding.

Main Results:

• The DAD enzyme adopts a cupin fold and forms dimers with a hydrophobic interface.
• The catalytic non-heme iron is coordinated by three histidine residues and a putative carbonate or formate ligand.
• The active site is a hydrophobic cavity, suggesting peroxide radical-mediated heterolysis of the substrate.

Conclusions:

• The determined structure provides insights into the unique catalytic mechanism of DAD.
• The active site architecture explains the enzyme's specificity for C-C bond cleavage in the substrate substituent.
• This study lays the groundwork for further investigations into dioxygenase mechanisms.