Electron transfer in ruthenium-modified spinach plastocyanin mutants

Area of Science:

• Biochemistry
• Biophysical Chemistry
• Spectroscopy

Background:

• Plastocyanin (Pc) is a copper-containing protein involved in electron transfer.
• Site-directed mutagenesis allows for targeted modification of protein properties.
• Ruthenium complexes are photoactive and can be used as probes in electron transfer studies.

Purpose of the Study:

• To investigate electron transfer (ET) dynamics in modified plastocyanin-ruthenium complexes.
• To determine the relationship between metal-to-metal distance and ET rates.
• To measure the reorganization energy of the copper-to-ruthenium ET reaction.

Main Methods:

• Site-directed mutagenesis to create histidine mutants of spinach plastocyanin.
• Covalent attachment of a photoactive ruthenium complex to surface-exposed histidine residues.
• Characterization using optical absorption, CD, and EPR spectroscopy.
• Time-resolved optical spectroscopy with an external quencher to study electron transfer kinetics.

Main Results:

• Pc-Ruthenium complexes were successfully synthesized and characterized.
• Electron transfer rates showed an exponential dependence on metal-to-metal separation (decay factor of 1.1 Å⁻¹).
• A reorganization energy of 1.2 eV was determined for the copper-to-ruthenium ET reaction.
• Temperature dependence of the driving force was found to be significant.

Conclusions:

• The study provides quantitative data on electron transfer mechanisms in metalloproteins.
• The findings contribute to understanding the principles governing biological electron transport.
• The methodology allows for probing intramolecular electron transfer in modified proteins.