Bitter taste puzzle is licked

Researchers have taken a big leap forward in understanding our sense of taste by identifying the genes that enable us to recognise bitter substances.

This discovery could eventually lead to medicines which mask their own bitter taste, an important goal given that studies have shown that patients often avoid taking vital drugs if they taste foul.

The research might even result in agricultural sprays which the target the taste buds of pests to prevent them from eating crops.

Cells in our tongues sense four basic tastes - sweet, salty, sour and bitter - plus a fifth, monosodium glutamate. But until now scientists did not know exactly how we tasted bitter and sweet things.

Several different research groups have been mining genomic data and contributing to the discovery of bitter taste receptors.

Human Genome Project

Scientists at Harvard Medical School used information from the Human Genome Project (HGP), which by this June will have sequenced nearly all the DNA in our chromosomes.

"The HGP is a fantastic resource," said neurobiologist Dr Linda Buck, one of the research team. "We couldn't have done the work without it."

The Harvard team began by looking through a database of mouse genes. They zoomed in on the part of a chromosome where genetic mutations had been shown to knock out a rodent's sense for bitter food.

They then used the HGP's powerful database technology to call up the corresponding location in human DNA. Trawling though it, they found a whole cluster of genes coding for cell receptors.

These are proteins that poke out of the cell wall and signal the presence of a particular taste molecule. They do this by having a complementary shape to the taste molecule, rather like a lock and key.

To prove that the receptor genes they had found did in fact produce the taste receptors, the scientists analysed the cells in mouse taste buds. They found that the genes did indeed produce receptor proteins and furthermore the genes were not active in any other cells in the body.

Could help the medicine go down

"These findings are important in explaining why we perceive so many tastes as bitter," said Dr Buck. "It's because there are so many types of receptors for this one taste. Some of these may turn out to be sweet receptors, but my money is on most of them being for bitter tastes."

Dr Buck plans to use the information to find out what happens in our brains when we taste bitter foods.

But pharmaceutical companies may well be interested in developing additives to medicines that lock up bitter-taste receptors. This would stop us from perceiving the terrible taste of many medicines.

Chemical companies may also benefit from research into insects' sense of taste as a safer and more environmentally friendly alternative to pesticides.

The research is published in the journal Nature in which Dr Stuart Firestein of Columbia University comments: "Of course, these developments are not trivial. But with the receptors that we now have and the application of a similar strategy to newly available genome data, it should be well within our power to lick these problems."