Opsins binds G alpha-t

Stable Identifier
Reaction [transition]
Homo sapiens
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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). Photon activated-opsins can bind to G(t) alpha subunits and stimulate them. Activation of the G(t) alpha subunit 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
8406495 Characterization of the gene encoding human cone transducin alpha-subunit (GNAT2)

Fong, SL, Morris, TA

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

Chen, CK

Rev Physiol Biochem Pharmacol 2005
Catalyst Activity

guanyl-nucleotide exchange factor activity of Opsins:photon [photoreceptor disc membrane]

Orthologous Events
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