Opsins act as GEFs for G alpha-t

Stable Identifier
R-HSA-420883
Type
Reaction
Species
Homo sapiens
Compartment
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Summation

Transducin (Gt) is a heterotrimeric G protein encoded by GNAT genes and is naturally expressed in vertebrate retina rods and cones. There are two types, alpha-1 chain (expressed in rods by GNAT1) (Lerea CL et al, 1989) and alpha-2 chain (expressed in cones by GNAT2) (Morris TA and Fong SL, 1993). Stimulated opsins can act as GEFs for G (t) alpha subunits by replacing GDP with GTP. Consequently, the G (t) alpha subunit is activated and results in the "vertebrate phototransduction cascade" (Chen CK, 2005). Cyclic GMP Phosphodiesterase is activated which lowers cGMP levels (an intracellular second messenger molecule). Lower cGMP levels can then lead to the closure of cGMP-regulated Na+ and Ca2+ ion channels and a hyperpolarized membrane potential.

Literature References
PubMed ID Title Journal Year
2534964 Alpha transducin is present in blue-, green-, and red-sensitive cone photoreceptors in the human retina

Lerea, CL, Bunt-Milam, AH, Hurley, JB

Neuron 1989
8406495 Characterization of the gene encoding human cone transducin alpha-subunit (GNAT2)

Morris, TA, Fong, SL

Genomics 1993
16634148 The vertebrate phototransduction cascade: amplification and termination mechanisms

Chen, CK

Rev Physiol Biochem Pharmacol 2005
Participants
Participant Of
Catalyst Activity
Catalyst Activity
Title
guanyl-nucleotide exchange factor activity of Opsins:photon [photoreceptor disc membrane]
Physical Entity
Activity
Orthologous Events
Authored
Reviewed