Structural and Functional Characterization of a Novel 4,5-Dihydroxyphthalate Decarboxylase for Protocatechuic Acid...

Area of Science:

• Biochemistry
• Environmental Microbiology
• Enzymology

Background:

• Phthalate esters (PAEs) are persistent environmental pollutants.
• PAE degradation involves 4,5-dihydroxyphthalate (4,5-DHP) as a key intermediate.
• 4,5-DHP is converted to protocatechuate (PCA), a compound with therapeutic potential.

Purpose of the Study:

• To elucidate the molecular architecture and catalytic mechanism of a novel 4,5-DHP decarboxylase (DhpD).
• To characterize the enzyme's activity and identify key residues for its function.
• To explore a potential biosynthetic pathway for PCA.

Main Methods:

• Isolation and characterization of DhpD (PAE-UM2851) from ultramicrobacteria.
• Enzymatic assays to determine optimal activity conditions (pH, temperature) and kinetic parameters (Km).
• Fourier-transform infrared (FTIR) spectroscopy to confirm product formation.
• Structure-function analysis to identify essential catalytic residues.

Main Results:

• PAE-UM2851 functions as a 4,5-DHP decarboxylase, converting 4,5-DHP to PCA.
• Optimal activity observed at pH 7.5 and 45 °C, with a Km of 911.5 μM.
• FTIR confirmed decarboxylation via reduced CO and OH vibrational modes.
• Five conserved residues (Ser57, Arg84, Thr115, Lys150, His223) are crucial for regioselective catalysis.

Conclusions:

• The study clarifies the catalytic mechanism of DhpD in PAE metabolism.
• Identified key residues provide insights into enzyme regulation and substrate specificity.
• The findings suggest a potential biosynthetic route for producing PCA.