Beans spill their secrets for a healthy diet
Good news is on the way for anyone who craves the health benefits of soybeans, but hasn't acquired a taste for tofu. Scientists have identified an enzyme for producing genistein--the substance that confers soybeans with their health-promoting benefits--and have transferred it into another plant. By demonstrating that this enzyme works efficiently in a well-studied laboratory plant, their work suggests food crops more suited to a Western palate might one day be engineered with the health-boosting nutrient.
The abundance of soya in the traditional Japanese diet is thought to contribute to a lower rate of heart disease, osteoporosis, and certain kinds of cancer in the population. Soybeans' health benefits are attributable to high levels of isoflavone molecules, such as genistein, that resemble the sex hormone estrogen. In plants, isoflavones are almost exclusively found in soybeans and other legumes, where they help ward off diseases and play a role in nitrogen absorption. In humans, their biochemical action is still a bit of a mystery, but scientists believe they block certain harmful effects of estrogen by binding to estrogen receptors that relay hormone signals to certain tissues of the body.
Unfortunately, in most Western diets, the intake of soy-based foods is very low and the isoflavone content of soy is variable. Now a team of scientists headed by Brian McGonigle has identified isoflavone synthase--the enzyme responsible for isoflavone production in soy. Using the knowledge that isoflavone synthase has characteristics of an important and well-studied class of enzymes called cytochrome P450s, the scientists searched their collection of soybean DNA sequences for candidate genes and introduced them into a yeast strain that had been engineered to produce a plant version of another enzyme known to be involved in isoflavone synthesis. To see whether the yeast contained the enzyme they were looking for, they then isolated the yeast's cellular membranes (which contained the accessory protein and the candidate protein from soybean) and chemical precursors for isoflavone synthesis. When they found a strain that produced genistein, they knew they had identified the isoflavone synthase gene. As a final step, they transferred the gene into Arabidopsis, a laboratory plant that normally doesn't produce genistein, but does contain some of its precursors. Sure enough, in the transgenic plants, the newly introduced isoflavone synthase turned isoflavone precursors into genistein. Future work could investigate whether the enzyme can be introduced into crops destined for human consumption.
Contact
(Author)
Dr. Brian McGonigle
DuPont Agricultural Products
Experimental Station
P.O. Box 80402
Wilmington, DE 19880-0402
Fax 302 695 8480
[email protected]
Contact
(Research News & Views)
Dr. Jerry Shay
University of Texas - Southwestern Medical Center
Department of Cell Biology
5323 Harry Hines Blvd.
Dallas, TX 75235-9039
Tel: 214 648 3282
Fax: 214 648 8694
[email protected]
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