Ultrafast Light-Driven Electron Transfer in a Ru(II)tris(bipyridine)-Labeled Multiheme Cytochrome

Area of Science:

• Biochemistry and Biophysics
• Bioinorganic Chemistry
• Spectroscopy

Background:

• Multiheme cytochromes are crucial for electron transport in biological systems.
• Understanding electron transfer factors in these proteins is essential for bionanoelectronic applications.
• The structure-function relationship of electron transfer in multiheme cytochromes remains an active area of research.

Purpose of the Study:

• To investigate the heme-heme electron transfer dynamics in the multiheme cytochrome STC from *Shewanella oneidensis*.
• To determine the influence of protein structure and labeling on electron transfer rates.
• To establish the utility of ultrafast spectroscopy for studying interheme electron transfer.

Main Methods:

• Site-selective labeling of STC with a Ruthenium(II)(bipyridine)3 dye.
• Ultrafast transient absorbance spectroscopy to monitor light-driven electron transfer.
• Kinetic modeling, molecular dynamics simulations, and density functional theory calculations for corroboration.

Main Results:

• Resolved ultrafast electron transfer rates between specific hemes in STC.
• Heme IV → Heme III transfer rate: 87 × 10^6 s^-1; Heme I → Heme II transfer rate: 125 × 10^6 s^-1.
• Observed electron transfer rates are significantly faster than previously computed values for unlabeled STC.

Conclusions:

• The study demonstrates that Ru-labeling and ultrafast spectroscopy can effectively resolve interheme electron transfer dynamics.
• The T-shaped heme packing arrangement in STC facilitates rapid electron transfer.
• These findings highlight the potential of multiheme cytochromes in bionanoelectronic devices.