Iron oxidation state modulates active site structure in a heme peroxidase

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Ascorbate peroxidase (APX) is crucial for plant oxidative stress response.
• The W41A variant of APX exhibits unique distal histidine (His42) dynamics.
• Previous work showed His42 dissociation upon substrate binding in ferric W41A APX.

Purpose of the Study:

• To investigate the effect of heme iron reduction on His42 binding in W41A APX.
• To elucidate the structural and dynamic changes associated with heme reduction.
• To understand the interplay between oxidation state and conformational flexibility in heme proteins.

Main Methods:

• X-ray crystallography to determine protein structure.
• Spectroscopic techniques to monitor heme environment.
• Ligand binding assays to assess protein-ligand interactions.

Main Results:

• Heme iron reduction in W41A APX triggers His42 dissociation from the ferrous heme.
• Structural data reveal a transient bis-histidine-ligated ferrous intermediate.
• Spectroscopic and binding data corroborate His42 dissociation upon reduction.

Conclusions:

• Conformational movement in the heme active site is regulated by both ligand binding and metal oxidation state.
• These findings provide insights into the regulatory mechanisms of heme proteins.
• The study contributes to understanding the dynamic nature of enzyme active sites.