Inter-cofactor protein remodeling rewires short-circuited transmembrane electron transfer

Area of Science:

• Biochemistry and Biophysics
• Photosynthesis Research
• Protein Engineering

Background:

• Intraprotein electron transfer (ET) is crucial for biological energy conversion, relying on precise control of cofactor environments.
• Efficient long-range ET often involves aromatic residues that facilitate electron conduction through intervening protein structures.
• The bacterial photosynthetic reaction center possesses a vestigial ET pathway with limited native function.

Purpose of the Study:

• To revitalize and enhance a dormant electron transfer pathway in the bacterial photosynthetic reaction center.
• To investigate the role of specific amino acid substitutions (tryptophan and threonine) in improving electron conduction.
• To optimize transmembrane charge separation efficiency through protein engineering.

Main Methods:

• Systematic substitution of amino acid residues, specifically introducing tryptophans, within the bacterial photosynthetic reaction center.
• Scanning for optimal tryptophan placement to identify improved electron conduction routes between tetrapyrrole and quinone cofactors.
• Investigating synergistic effects of combining tryptophan substitutions with threonine to modulate quinone binding and redox potential.

Main Results:

• Introduction of tryptophans identified significantly improved electron conduction pathways, revitalizing a vestigial ET route.
• Pairing tryptophans with threonine maximally enhanced a key ET step, achieving yields of approximately 95%.
• Combined substitutions dramatically improved transmembrane charge separation, demonstrating a highly efficient engineered pathway.

Conclusions:

• Engineered electron transfer pathways can be revitalized to achieve high efficiency in biological systems.
• Tryptophan and threonine substitutions are effective in enhancing electron conduction and modulating cofactor properties.
• This study demonstrates a successful redesign of a previously inactive pathway for significantly improved photosynthetic function.