Taste protein relays bitter signal.

Molecular neurobiologists have discovered a new protein, gustducin, that seems to reside only in the taste buds and may act as a messenger for bitter-taste signals.

This protein contains 354 amino acids, and it is the first found to be specific to taste cells, report Susan K. McLaughlin and her colleagues at the Roche Institute of Molecular Biology in Nutley, N.J. Gustducin represents a new variant of the G proteins, molecules known to relay sensory signals by setting off the cascade of chemical reactions that leads to the stimulation of a nerve cell.

The researchers were surprised at how much this new molecule looks like the transducins, G proteins in the eye's rods and cones, notes Robert F. Margolskee, who heads the Roche Institute group. Based on this similarity, the researchers infer that gustducin activates a particular enzyme known to be involved in the sensation of bitter.

The Roche researchers, who did their work in rats, found no gustducin in other parts of the tongue or in other tissue studied, they report in the June 18 NATURE. They hope to use this protein to help them find the receptor molecule that latches on to bitter substances in the mouth. "Our long-term plan is to try to recreate taste [perception] in a test-tube," Margolskee says.