betatransducin

Betatransducin, or the transducin beta subunit, is a component of the heterotrimeric G protein transducin involved in vertebrate phototransduction. It is the beta subunit of transducin and is encoded by the GNB1 gene in humans. In rod and cone photoreceptors, transducin comprises Gαt (GNAT1 or GNAT2), Gβ1 (GNB1), and Gγt (GNGT1). The Gβ subunits are WD40 repeat-containing proteins that form a beta-propeller structure and act as regulatory subunits, stabilizing the heterotrimer and mediating interactions with Gα, Gγ, receptors, and downstream effectors.

Functionally, betatransducin participates in the assembly of the transducin heterotrimer in the dark and facilitates efficient GDP-GTP exchange on the Gα subunit upon receptor activation. After photon absorption, Gαt releases Gβγ, and the subunits, along with regulators, help terminate signaling and promote reassociation of the inactive heterotrimer. Gβ subunits also influence membrane targeting and the kinetics of signaling, contributing to the precise control of the phototransduction cascade.

Distribution and significance-wise, Gβ1-containing subunits are expressed broadly, with the highest abundance in retinal photoreceptors where betatransducin is integral to light signal transmission. In the retina, proper function of the transducin beta subunit supports the activation of downstream effectors and the restoration of dark conditions.

See also G protein beta subunit, transducin, phototransduction.