Comments on the g tensor variations in selenium-substituted 2Fe-2S iron-sulfur proteins

Area of Science:

• Biochemistry
• Bioinorganic Chemistry
• Biophysics

Background:

• Reduced iron-sulfur proteins, specifically 2Fe-2S ferredoxins, are crucial in biological electron transfer.
• Understanding the electronic structure of these proteins is key to elucidating their function.
• Selenium substitution offers a tool to probe the active site environment.

Purpose of the Study:

• To investigate the electronic structure of selenium-substituted 2Fe-2S ferredoxins.
• To determine if a previously proposed model for native ferredoxins applies to selenium derivatives.
• To correlate experimental g values with structural distortions.

Main Methods:

• Electron paramagnetic resonance (EPR) spectroscopy to measure g values (gx, gy, gz).
• Analysis of g value correlations as a function of gy--gx.
• Comparison of experimental data with a theoretical model of rhombic distortion.

Main Results:

• A correlation between g values was observed in selenium-substituted ferredoxins, mirroring native proteins.
• The experimental data align with a model involving variable rhombic distortion at the iron site.
• Excellent agreement was achieved using g values from Fe(III)Se2S2 clusters in ZnS crystals for Fe(III).

Conclusions:

• The model of variable rhombic distortion successfully explains the electronic properties of selenium-substituted 2Fe-2S ferredoxins.
• Selenium substitution does not fundamentally alter the electronic behavior explained by this distortion model.
• This study validates the applicability of the rhombic distortion model across different ferredoxin derivatives.