Second-Shell Hydrogen Bond Impacts Transition-State Structure in Bacillus subtilis Oxalate Decarboxylase

Area of Science:

• Biochemistry
• Enzymology
• Bioinorganic Chemistry

Background:

• Metalloenzymes utilize metal ions for catalysis, with surrounding amino acids modulating their properties.
• Oxalate decarboxylase (OxDC) is a manganese-dependent enzyme crucial for oxalate metabolism.
• Second-shell interactions, beyond direct metal ligands, can influence metal ion redox states and reactivity.

Purpose of the Study:

• To investigate the role of a specific hydrogen bond (Glu101-Trp132) in modulating the redox properties of manganese in OxDC.
• To test the hypothesis that this second-shell interaction stabilizes the Mn(III) state during catalysis.

Main Methods:

• Heavy-atom kinetic isotope effect measurements were performed on a W132F OxDC variant.
• Electron paramagnetic resonance (EPR) spectroscopy was used to characterize manganese states.

Main Results:

• Removing the Glu101-Trp132 hydrogen bond increases the energy of the oxalate radical intermediate.
• Altered zero-field splitting parameters were observed for the Mn(II) ion in the W132F variant.
• The findings suggest the hydrogen bond stabilizes the Mn(III) ion during catalytic turnover.

Conclusions:

• The Glu101-Trp132 hydrogen bond plays a significant role in modulating the redox properties of the manganese ion in OxDC.
• Second-shell interactions are critical for fine-tuning metalloenzyme activity and stability.
• This study provides insights into the catalytic mechanisms of manganese-dependent enzymes.