Indiana University Research & Creative Activity

Food

Volume 30 Number 1
Fall 2007

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Milos Novotny
Milos Novotny
Photo courtesy Indiana University

mass spectrometry instrument
Ion mobility-mass spectrometry instrument
Photo by Roberta Kwok

Sweet Science

by Roberta Kwok

Sugar seems pretty simple. It's sweet, it's grainy or powdery, it makes your coffee taste better. Look closely, though, and it turns out that sugars do a lot more than feed us. Table sugar is just one of a huge class of sugar molecules--also known as carbohydrates or glycans--that play a role in everything from immune response to cancer metastasis to tick bites.

"There are whole areas where carbohydrates are important that don't really have anything to do with nutrition," says Douglas Sheeley, a research program director at the National Institutes of Health (NIH).

Sugars are attached to virtually all the cells in our bodies, acting like bar codes that help other cells recognize them. They're also attached to many of our proteins, the molecules responsible for carrying out important jobs like digesting food and fighting off infections. A single sugar molecule on red blood cells, for instance, determines whether a person's blood type is A, B, or O. Faulty sugar attachments can signal autoimmune diseases such as lupus or rheumatoid arthritis, as well as more serious disorders that can cause brain defects or premature death. And sugars have been found on the surfaces of unsavory agents like HIV, anthrax bacteria, and malaria parasites, giving scientists hope that a carbohydrate-based vaccine could help our immune systems neutralize these invaders.

Sugars haven't always been recognized as worthy of scientific scrutiny, however. As far back as the late 1800s, scientists, including the great Nobel Prize-winning chemist Emil Fischer, were predicting the biological importance of sugars, but nobody really paid attention.

"People just didn't care," says Milos Novotny, a Distinguished Professor and Lilly Chemistry Alumni Chair in the Department of Chemistry at Indiana University Bloomington. "Everybody jumped on DNA and proteins--for good reasons, because obviously they are important molecules. Sugars were neglected for a number of years."

Novotny admits that he didn't see the appeal of sugar molecules at first, either. When he was a young graduate student in Czechoslovakia, he thought it was "the most boring area."

A lot has changed since then. Novotny now leads the National Center for Glycomics and Glycoproteomics (NCGG) at IU Bloomington, a research center devoted to the study of carbohydrates. Funded by a $3.2 million grant from the NIH, the center's goal is to develop new technologies to analyze the notoriously difficult structures of sugars. More important, the center is using these tools to help biologists identify and measure sugars in living systems, with the hope that understanding sugars will eventually lead to new medical therapies.

"It's a resource for the community," says Sheeley, who heads the glycomics program at the NIH's National Center for Research Resources. "That's really the most important part of the IU center's mission: to help people solve problems they wouldn't otherwise be able to solve."

Housed in a few rooms filled with humming machines and dangling wires, the center looks like a fairly modest enterprise. "From here to the wall is NCGG," says the center's assistant director, Yehia Mechref, on a tour of the facility, marking the middle of one room with his arm. But these rooms--along with the laboratories of a few other IU faculty--contain some of the latest and greatest technology for sugar analysis. Now in its third year, the center has leading-edge capabilities that have attracted scientists from Italy, the United Kingdom, the Czech Republic, and the United States.

"Our services are not just local," says Mechref, a senior scientist in the Department of Chemistry who coordinates many of the center's services along with Randy Arnold, the proteomics manager. "It's an international collaboration."

One of the center's main projects is close to home, at the IU School of Medicine. With IU cancer researchers Linda Malkas, Robert Hickey, and Christopher Sweeney, the chemists at NCGG are studying how sugar patterns change in patients with breast or prostate cancer.

Scientists have known for years that sugars and cancer are connected, says Malkas, who studies breast cancer and holds the Vera Bradley Chair of Oncology at the School of Medicine. Cancer cells, for instance, switch from an oxygen-based to sugar-based diet, and the sugars attached to cancer cells appear different from those on normal cells. But no one quite knows how all these sugar-related changes fit together. "We just know that sugars get screwed up in cancer," Malkas says.

By peeling sugars off their proteins and analyzing them, Novotny's group can create a "profile" of the sugars in a patient's blood sample. One of the center's strengths is its ability to process samples quickly--almost 10 per minute--using only a tiny amount of blood each time. The first scientists to study the sugar content of blood weren't so lucky. "They had to work with liters and liters of blood to isolate enough material," says Novotny. "We can do it out of just barely 10 microliters of blood. So the sensitivity has phenomenally improved."

With a flood of new data, the chemists need some serious technology support from computer scientists. Haixu Tang, a NCGG co-investigator and professor in the IU School of Informatics, provides speedy software to interpret the results, allowing the researchers to look at all of the sugars in a blood sample instead of just a few. This comprehensive survey is typical of glycomics, the study of all sugars in a living system. Tang says glycomics is one of the newer "so-called ‘omics' approaches," joining older fields such as genomics, the study of all genes in an organism, and proteomics, the study of all proteins.

Eventually, the NCGG group hopes to find a subtle tweak in sugar levels that could act as a red flag for cancer. They've already detected differences between the sugar profiles of healthy patients and patients with advanced (stage 4) breast cancer. With more samples from cancer patients in stages 1 through 3, they might have the makings of a clinical test for early cancer detection. "This is all virgin territory, we have no idea," says Malkas. "But it's a very beautiful vista out there."

Scattered throughout the Chemistry Building at IU Bloomington, three other labs are working on the nuts and bolts of NCGG's operation. Co-investigators David Clemmer, James Reilly, and Stephen Jacobson are out to tackle the sticky problem of sugar structures, each in his own way.

The organizations of sugars, which are made by linking simple molecules like glucose, are enough to make even an experienced chemist dizzy. "The structures are very intricate," says Novotny. "It's kind of mind-boggling how many different ways you can put these basic sugar units together." Unlike DNA and proteins, which are linear chains, sugars can have elaborate branches. There is no easy way to synthesize sugars or figure out their chemical sequence. To make things more complicated, many sugars look very similar, with only minor--but important--differences between them. Sheeley gives the example of starch and cellulose, two carbohydrates that are both made of repeating glucose units.

"One thing you eat, and one you make wood with," he says. A lollipop may contain both, but the exact arrangement of the glucose molecules "makes all the difference between the candy and the stick."

Clemmer, who holds the Robert and Marjorie Mann Chair in the chemistry department, has developed an instrument to distinguish the toughest look-alikes of all. These twin sugars, called isomers, have slightly different 3-D structures but the exact same mass, which makes them difficult to separate with traditional analytical methods. To solve this problem, Clemmer relies on a tongue-twister technology called "ion mobility-mass spectrometry," carried out by an equally twisted-looking set of vacuum tubes and colored wires. The machine whisks the isomers through a vacuum tube, relying on drag force to slow down the larger isomer. The smaller isomer will zip through the tube more quickly, allowing Clemmer to pull apart the two molecules.

Meanwhile, both Reilly and Jacobson are cutting sugars down to size. Reilly's latest method zaps sugars into smaller fragments with a laser, which can reveal clues to a sugar's detailed structure. Jacobson's expertise is in microfluidics, or analyzing extremely small amounts of liquid. "He can do everything in a miniaturized form," says Mechref. While a standard analysis of a liquid sample takes about half an hour, Jacobson's instruments can get it done in three minutes.

By pooling their talents, the chemists at NCGG are coming closer to cracking the sugar code. "They have a wealth of expertise in analytical chemistry," says Sheeley. "And an environment where they can work together, where they can approach this multidisciplinary problem, is a good thing for this kind of enterprise."

Still, scientists have a long way to go before they find the Holy Grail of carbohydrates: the glycome, or the complete set of sugars in the human body. Unlike the human genome, which has a specific size, no one knows how many sugars we humans are capable of making. And the glycoproteome, or all the possible combinations of sugars and proteins, is even more overwhelming.

"That's why glycobiology is the most incredible frontier, because we don't know the limitations," says Richard Cummings, the William Patterson Timmie Professor in the Department of Biochemistry at Emory University who chairs the NCGG's advisory board. "We won't know when we're finished."

Roberta Kwok is a freelance science writer. She is currently studying science communication at University of California at Santa Cruz.