Transducin

Transducin

Illustration of the interaction between rhodopsin and transducin.

Transducin is a G protein found in the retina of the eye. It plays a crucial role in the phototransduction cascade, which is the process by which light is converted into electrical signals in the photoreceptor cells.

Structure

Transducin is a heterotrimeric protein composed of three subunits: alpha (_), beta (_), and gamma (_). The alpha subunit is responsible for binding and hydrolyzing GTP, while the beta and gamma subunits form a stable dimer that anchors the protein to the cell membrane.

Function

Transducin is activated by the rhodopsin receptor, a G protein-coupled receptor (GPCR) that is activated by light. When rhodopsin absorbs a photon, it undergoes a conformational change and activates transducin by facilitating the exchange of GDP for GTP on the alpha subunit. The activated alpha subunit then dissociates from the beta-gamma dimer and interacts with phosphodiesterase, leading to a decrease in cGMP levels and the closure of cGMP-gated ion channels. This results in the hyperpolarization of the photoreceptor cell and the transmission of a signal to the brain.

Role in Vision

Transducin is essential for scotopic vision, which is vision under low-light conditions. It is primarily found in rod cells, which are responsible for detecting light intensity and are highly sensitive to low levels of light. In bright light conditions, transducin is less active, and cone cells take over the role of phototransduction.

Related Proteins

Transducin is part of a larger family of G proteins that are involved in various signaling pathways throughout the body. Other members of this family include Gs, Gi, and Gq proteins, each of which interacts with different receptors and effectors to mediate diverse physiological responses.

Clinical Significance

Mutations in the genes encoding transducin subunits can lead to visual disorders. For example, mutations in the GNAT1 gene, which encodes the alpha subunit of transducin, have been associated with night blindness and other retinal dysfunctions.

Related Pages

• Phototransduction
• Rhodopsin
• G protein-coupled receptor
• Retina