CO₂/bicarbonate modulates cone photoreceptor ROS-GC1 and restores its CORD6-linked catalytic activity

Area of Science:

• Biochemistry
• Molecular Biology
• Vision Science

Background:

• Photoreceptor cells are crucial for vision, converting light into electrical signals.
• Guanylate cyclase (GC) enzymes play a key role in phototransduction.
• Cone cells, responsible for color vision, have unique signaling pathways.

Purpose of the Study:

• To investigate the role of gaseous carbon dioxide (CO2) in modulating photoreceptor guanylate cyclase 1 (ROS-GC1) activity.
• To elucidate the mechanism by which CO2 affects cone phototransduction.
• To understand the link between CO2 modulation of ROS-GC1 and cone-rod dystrophy type 6 (CORD6).

Main Methods:

• Utilized a recombinant reconstituted system mimicking cellular conditions.
• Investigated the interaction of CO2, carbonic anhydrase II (CAII), and bicarbonate with ROS-GC1.
• Analyzed the effects of a specific ROS-GC1 mutation (R787C) associated with CORD6.

Main Results:

• Demonstrated that CO2 directly activates ROS-GC1 via carbonic anhydrase II (CAII) and bicarbonate production.
• Showed that the CO2 pathway is calcium (Ca2+)-independent and synergizes with Ca2+-modulated phototransduction.
• Identified that a R787C mutation in ROS-GC1 causes CORD6 by altering enzyme activity and Ca2+ sensitivity, with bicarbonate partially rescuing the defect.

Conclusions:

• CO2 acts as a novel modulator of cone phototransduction through ROS-GC1 activation.
• The CO2-bicarbonate pathway provides a calcium-independent mechanism that complements and enhances cone signaling.
• Understanding this pathway and its link to CORD6 offers insights into retinal disease mechanisms and potential therapeutic targets.