Transducin

Transducin is a protein that is integral to the function of photoreceptor cells in the retina of the eye. It is a type of G protein, which are proteins that act as molecular switches inside cells, and is involved in the transmission of signals from light-sensitive molecules to other parts of the cell.

Structure

Transducin is a heterotrimeric G protein, meaning it is composed of three different subunits: alpha (Gα), beta (Gβ), and gamma (Gγ). The Gα subunit is the part of the protein that binds to guanosine triphosphate (GTP) and guanosine diphosphate (GDP), molecules that are crucial for the protein's function.

Function

In the dark, the Gα subunit of transducin is bound to GDP and the protein is inactive. When light hits the retina, it causes a change in the shape of a molecule called rhodopsin, which is located in the photoreceptor cells. This change in shape allows rhodopsin to bind to the Gα subunit of transducin, causing GDP to be released and GTP to bind in its place. This activates the transducin, which then separates from the rhodopsin and splits into its Gα and Gβγ subunits.

The Gα subunit, now activated, binds to another protein called phosphodiesterase, activating it as well. This leads to a decrease in the concentration of a molecule called cyclic guanosine monophosphate (cGMP) in the cell. As the concentration of cGMP decreases, the ion channels that it was keeping open close, leading to a change in the electrical charge of the cell. This change in charge is what ultimately leads to the transmission of a signal to the brain, allowing us to perceive light.

Clinical significance

Mutations in the genes that encode for the subunits of transducin can lead to various forms of retinal degeneration, including retinitis pigmentosa and congenital stationary night blindness. These conditions are characterized by a progressive loss of vision due to the death of photoreceptor cells in the retina.

See also

• G protein
• Photoreceptor cell
• Rhodopsin
• Phosphodiesterase
• Retinitis pigmentosa
• Congenital stationary night blindness

Transducin Resources
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