Everything about Transducin totally explained
Transducin (also called G
t) is a heterotrimeric
G protein that's naturally
expressed in
vertebrate retina rods and cones (a different Transducin gene is expressed in each cell type). Heterotrimeric Transducin (alpha-beta-gamma
subunits) is activated by a conformational change in
rhodopsin due to the
absorption of a
photon by rhodopsin's active group
retinal; Activation causes the GDP bound to the alpha subunit to be exchanged with GTP from solution and results in activated alpha dissociating from beta-gamma. Active Transducin-alpha then causes
cyclic GMP Phosphodiesterase to increase its activity, thereby lowering the concentration of
cGMP, an intracellular second-messenger molecule. Decrease in cGMP concentration leads to the closure of cGMP-regulated
ion channels and a hyperpolarized
membrane potential. This chain of signaling events is also called "the vertebrate phototransduction cascade".
The termination of Transducin activity occurs when (active) GTP bound Transducin is hydrolyzed to Transducin-GDP, a process which is accelerated by a complex containing an RGS (
Regulator of G-protein signaling)-protein and the gamma-subunit of the effector, cyclic GMP Phosphodiesterase.
Genes
Further Information
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