Skip to main content

Molecular basis for branched steviol glucoside biosynthesis in Stevia rebaudiana

New research reveals the molecular machinery behind the high-intensity sweetness of Stevia rebaudiana. The results could be used to engineer new non-caloric products without the aftertaste that many associate with sweetener marketed as Stevia.

Although the genes and proteins in the biochemical pathway responsible for stevia synthesis are almost completely known, this is the first time that the three-dimensional structure of the proteins that make rebaudioside A or 'RebA,' the major ingredient in the product Stevia, has been published, according to the researchers of a new paper in the Proceedings of the National Academy of Sciences.

Dlium Molecular basis for branched steviol glucoside biosynthesis in Stevia rebaudiana

"If someone is diabetic or obese and needs to remove sugar from their diet, they can turn to artificial sweeteners made from chemical synthesis (aspartame, saccharin, etc), but all of these have 'off-tastes' not associated with sugar, and some have their own health issues," said Joseph Jez of the Washington University in St. Louis.

"Stevias and their related molecules occur naturally in plants and are more than 200 times sweeter than sugar. They've been consumed for centuries in Central and South America, and are safe for consumers," Jez said.

"Many major food and beverage companies are looking ahead and aiming to reduce sugar/calories in various projects over the next few years in response to consumer demands worldwide," he said.

Researchers determined the structure of the RebA protein by X-ray crystallography. Their analysis shows how RebA is synthesized by a key plant enzyme and how the chemical structure needed for that high-intensity sweetness is built biochemically.

To make something 200 times sweeter than a single glucose molecule, the plant enzyme decorates a core terpene scaffold with three special sugars. That extra-sweet taste from the stevia plant comes with an unwanted flavor downside, however.

"For me, the sweetness of Stevia comes with an aftertaste of licked aluminum foil. The taste is particular to the predominant molecules in the plant leaf: the stevioside and RebA. It is their chemical structure that hits the taste receptors on the tongue that trigger 'sweet,' but they also hit other taste receptors that trigger the other tastes," Jez said.

"RebA is abundant in the stevia plant and was the first product made from the plant because it was easy to purify in bulk. Call this 'Stevia 1.0'. But in the leaf are other related compounds with different structures that hit the 'sweet' without the aftertaste. Those are 'Stevia 2.0,' and they will be big," said Jez.

Many consumers experience this slightly metallic aftertaste. There are many ways that the newly published protein structure information could be used to help improve sweeteners.

"One could use the snapshot of the protein that makes RebA to guide protein engineering efforts to tailor the types and/or pattern of sugars in the stevias. This could be used to explore the chemical space between 'sweet' and 'yuck'," Jez said.

"There are also molecules in other plants that are not 'stevias' but can deliver intense sweetness. We could use the information of how the stevia plant does it as a way of finding those details," he said.

Journal : Soon Goo Lee et al. Molecular basis for branched steviol glucoside biosynthesis, PNAS, June 10, 2019, DOI:10.1073/pnas.1902104116

Popular Posts

Thomas Sutikna lives with Homo floresiensis

BLOG - On October 28, 2004, a paper was published in Nature describing the dwarf hominin we know today as Homo floresiensis that has shocked the world. The report changed the geographical landscape of early humans that previously stated that the Pleistocene Asia was only represented by two species, Homo erectus and Homo sapiens . The report titled "A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia" written by Peter Brown and Mike J. Morwood from the University of New England with Thomas Sutikna, Raden Pandji Soejono, Jatmiko, E. Wahyu Saptomo and Rokus Awe Due from the National Archaeology Research Institute (ARKENAS), Indonesia, presents more diversity in the genus Homo. “Immediately, my fever vanished. I couldn’t sleep well that night. I couldn’t wait for sunrise. In the early morning we went to the site, and when we arrived in the cave, I didn’t say a thing because both my mind and heart couldn’t handle this incredible moment. I just went down...

Black potato (Coleus rotundifolius)

Black potato ( Coleus rotundifolius ) is a species of plant in Lamiaceae, herbaceous, fibrous roots and tubers, erect and slightly creeping stems, quadrangular, thick, and slightly odorous. Single leaves, thick, membranous, opposite and alternate. Leaves are oval, dark green and shiny on the upper side, bright green on the lower side. Up to 5 cm long, up to 4 cm wide, slightly hairy and pinnate leaf veins. Leaf stalks up to 4 cm long. Small, purple flowers. Star-shaped petals, lip-shaped crown, dark to light purple with a slightly curved tube shape. Flowering from February-August. Small tubers, brown and white flesh and tuber length 2-4 cm. Kingdom: Plantae Phylum: Tracheophyta Subphylum: Angiospermae Class: Magnoliopsida Order: Lamiales Family: Lamiaceae Subfamily: Nepetoideae Tribe: Ocimeae Subtribe: Plectranthinae Genus: Coleus Species: Coleus rotundifolius

Wild durian (Cullenia exarillata)

Wild durian ( Cullenia exarillata ) is a species of plant in the Malvaceae, a tall tree with smooth, greyish-white bark, peeling on older trees, a straight trunk, horizontal branches and often with a series of knob-like tubercles for flower and fruit attachment. C. exarillata has young branches and the underside of the leaves is covered with golden brown peltate or shield-like scales. The leaves are single, alternate, glabrous, glossy green on the upper side and covered with silvery or orange peltate scales on the underside. Hermaphroditic flowers are tubular and also covered with golden brown scales, 4-5 cm long and cream or reddish brown in color. Flowers have no petals, formed of tubular bracteoles and tubular calyxes, 5-lobed. Fruit is round, 10-13 cm in diameter, covered with thorns and clustered along the branches. Many seeds, reddish brown, 4-5 cm long and 2-3 cm wide. The seeds are enclosed by a fleshy, whitish aril. The fruit splits open when ripe and dries to release the s...