cGMP-specific phosphodiesterase type 6 (PDE6)

cGMP-specific phosphodiesterase type 6 (PDE6) is the central effector enzyme of the vertebrate phototransduction cascade, primarily located in the outer segments of rod and cone photoreceptor cells [NIH, Wikipedia]. It exists as a heterotetrameric complex in rods (comprising PDE6A, PDE6B, and two PDE6G subunits) and a homotetrameric complex in cones (comprising two PDE6C and two PDE6H subunits) [NIH, UniProt]. In the dark, PDE6 activity is inhibited by its gamma subunits; upon light stimulation, the G-protein transducin (Gαt) binds to these subunits and relieves the inhibition, allowing for the rapid hydrolysis of cyclic guanosine monophosphate (cGMP) [NIH, StatPearls]. This drop in cGMP levels triggers the closure of cGMP-gated ion channels, leading to membrane hyperpolarization and the transmission of visual signals to the brain [Wikipedia, NIH]. Mutations in the genes encoding PDE6 subunits are a major cause of inherited retinal dystrophies, such as retinitis pigmentosa and achromatopsia [NIH, Wikipedia]. While not typically a primary therapeutic target, PDE6 is a significant off-target for phosphodiesterase type 5 (PDE5) inhibitors like sildenafil and vardenafil, which can cause transient visual side effects such as cyanopsia (blue-tinted vision) and photophobia due to cross-reactivity with the PDE6 catalytic domain [NIH, StatPearls]. Therapeutic strategies targeting PDE6 currently focus on gene replacement therapies to restore function in patients with inherited retinal degenerations [NIH].

Other names

GMP-PDEPhotoreceptor phosphodiesteraseRod cGMP-specific 3',5'-cyclic phosphodiesteraseCone cGMP-specific 3',5'-cyclic phosphodiesterasePDE6APDE6BPDE6CPDE6GPDE6HPDE6D

Inhibition of the catalytic hydrolysis of cyclic guanosine monophosphate (cGMP) to 5'-GMP, leading to elevated cGMP levels in photoreceptor cells and preventing the closure of cGMP-gated ion channels [NIH].