Quantification of light-induced miniSOG superoxide production using the selective marker, 2-hydroxyethidium

Area of Science:

• Biochemistry and Molecular Biology
• Cell Biology
• Photochemistry

Background:

• Genetically-encoded photosensitizers (RGPs) enable controlled reactive oxygen species (ROS) production for applications like cell ablation.
• The specific ROS species generated by RGPs, including miniSOG, are often unclear due to indirect measurement methods.
• miniSOG, derived from phototropin 2, is known to produce singlet oxygen (¹O₂), but its superoxide (O₂⁻) production is uncharacterized.

Purpose of the Study:

• To clarify the reactive oxygen species (ROS) profile of the genetically-encoded photosensitizer miniSOG.
• To determine if miniSOG and its chromophore, flavin mononucleotide, produce superoxide (O₂⁻) in addition to singlet oxygen (¹O₂).
• To establish a reliable method for measuring O₂⁻ production in systems co-producing ¹O₂.

Main Methods:

• Utilized High-Performance Liquid Chromatography (HPLC) to separate dihydroethidium (DHE) oxidation products for quantifying O₂⁻.
• Validated DHE as an O₂⁻ indicator insensitive to ¹O₂ in mixed ROS systems.
• Measured light-dependent O₂⁻ production from purified miniSOG and flavin mononucleotide under specific light excitation.

Main Results:

• Demonstrated that dihydroethidium (DHE) is a suitable and specific probe for superoxide (O₂⁻) detection, unaffected by singlet oxygen (¹O₂).
• Confirmed that miniSOG, and its free chromophore flavin mononucleotide, produce both singlet oxygen (¹O₂) and superoxide (O₂⁻).
• Quantified miniSOG's superoxide production rate at approximately 4.0 µmol O₂⁻/min/µmol photosensitizer under 5.9 mW/mm² excitation at 470 nm, consistent across varying light fluences.

Conclusions:

• The genetically-encoded photosensitizer miniSOG generates both singlet oxygen and superoxide, necessitating consideration of O₂⁻ in its biological effects.
• Dihydroethidium (DHE) provides a reliable method for quantifying superoxide production in systems involving singlet oxygen.
• Future research and applications utilizing miniSOG should account for the dual ROS production (¹O₂ and O₂⁻) for accurate interpretation of phenotypes.