Gustducin

Gustducin is a G protein associated with taste and the gustatory system, found in some taste receptor cells. Research on the discovery and isolation of gustaducin is recent. It is known to play a large role in the transduction of bitter, sweet and umami stimuli. Its pathways (especially for detecting bitter stimuli) are many and diverse. Gustducin is a G protein associated with taste and the gustatory system, found in some taste receptor cells. Research on the discovery and isolation of gustaducin is recent. It is known to play a large role in the transduction of bitter, sweet and umami stimuli. Its pathways (especially for detecting bitter stimuli) are many and diverse. An intriguing feature of gustducin is its similarity to transducin. These two G proteins have been shown to be structurally and functionally similar, leading researchers to believe that the sense of taste evolved in a similar fashion to the sense of sight. Gustducin is a heterotrimeric protein composed of the products of the GNAT3 (α-subunit), GNB1 (β-subunit) and GNG13 (γ-subunit). Gustducin was discovered in 1992 when degenerate oligonucleotide primers were synthesized and mixed with a taste tissue cDNA library. The DNA products were amplified by the polymerase chain reaction method, and eight positive clones were shown to encode the α subunits of G-proteins, (which interact with G-protein-coupled receptors). Of these eight, two had previously been shown to encode rod and cone α-transducin. The eighth clone, α-gustducin, was unique to the gustatory tissue. Upon analyzing the amino-acid sequence of α-gustducin, it was discovered that α-gustducins and α-transducins were closely related. This work showed that α-gustducin's protein sequence gives it 80% identity to both rod and cone a-transducin. Despite the structural similarities, the two proteins have very different functionalities. However, the two proteins have similar mechanism and capabilities. Transducin removes the inhibition from cGMP Phosphodiesterase, which leads to the breakdown of cGMP. Similarly, α-gustducin binds the inhibitory subunits of taste cell cAMP Phosphodiesterase which causes a decrease in cAMP levels. Also, the terminal 38 amino acids of α-gustducin and α-transducin are identical. This suggests that gustducin can interact with opsin and opsin-like G-coupled receptors. Conversely, this also suggests that transducin can interact with taste receptors.