Sugar fuels life. But to power our cells, sugar molecules have to slip in and out of cells. And in humans, the sugar sometimes needs to travel deep into tissues such as the intestines or the brain, far removed from the bloodstream.
Thanks to technological advances, scientists are still making new discoveries about these basic processes. And now, a team led by Stanford molecular biologist Liang Feng, PhD, and Carnegie Institution/Stanford biologist Wolf Frommer, PhD, has unraveled the molecular structure and function of a type of protein that straddles cell membranes, allowing sugar to pass.
The name of the compound — oh, those scientists and their senses of humor — is SWEET, which stands for "Sugars Will Eventually be Exported Transporters." SWEETs are found in all sorts of creatures, including humans, and plants; bacteria have semiSWEETs that are about half the size of a SWEET.
To determine the structure of these super-small proteins, Feng and his team used powerful X-ray equipment at the Argonne National Laboratory in Illinois and the Stanford Synchrotron Radiation Lightsource on campus. "Before our study, we had no idea what the protein looked like and how it could function," Feng told me.
As described in a paper published earlier this month in Nature, Feng and his colleagues learned that SWEET actively changes shape to swallow sugar, unlike a fixed channel such as a train tunnel. SWEET swings open jaws like a crocodile, clamps them shut, then shoots the sugar into the cell interior.
SWEETs, and the two other types of sugar transporters found in humans, could play a prominent role in a variety of human diseases, including diabetes, although most research now has been done in plants. The project produced what Feng calls "snapshots" of SWEET transporting sugar. Next, he plans to develop a moving "video" of the protein.
"We need to understand the blueprint of this machinery," Feng said. "What we learn could be used to improve crop yield or to design drugs that can help with sugar-related diseases such as diabetes."
Becky Bach is a former park ranger who now spends her time writing about science or on her yoga mat. She is a science-writing intern in the Office of Communications and Public Affairs.
Previously: Civilization and its dietary (dis)contents: Do modern diets starve our gut-microbial community?, Joyride: Brief post-antibiotic sugar spike gives pathogens a lift, Short and sweet: Three days in a sugar solution, and you've got your see-through tissue sample
Image courtesy of Liang Feng