FUNCTIONAL EXPRESSION OF THE TASTE SPECIFIC G-PROTEIN, ALPHA-GUSTDUCIN

The taste-specific G-protein alpha-subunit, alpha-gustducin, was expre ssed using a baculovirus based system. alpha-Gustducin was demonstrate d to be myristoylated and was also palmitoylated in insect larval cell s. Recombinant alpha-gustducin was purified to homogeneity, Neither re ceptors nor effecters that interact with gustducin in taste are known. However, alpha-gustducin has a close structural similarity to the vis ual G-protein, alpha-transducin. Therefore alpha-gustducin was reconsi tituted with components of the visual system to determine the degree o f its functional similarity with a-transducin. Despite the fact that t he sequences of alpha-gustducin and alpha-transducin share only 80% id entity-with each other, the interactions and functions of these two pr oteins were quantitatively identical. These included the interaction w ith receptor, bovine rhodopsin, with effector, bovine retinal cyclic G MP-phosophodiesterase, and with bovine brain and retinal G-protein bet a gamma-heterodimers; receptor-catalysed GDP-GTP exchange and the intr insic GTPase activity of alpha-gustducin and alpha-transducin were als o identical, G(i) alpha which is 70% identical with alpha-transducin i nteracts with different receptor and effector proteins and has very di fferent guanine-nucleotide binding properties. Therefore, the function al equivalence of alpha-gustducin and alpha-transducin suggest that ta ste buds are likely to contain receptor and effector proteins that sha re many properties with their retinal equivalents.