Diabetes Research Gets a New Tool
Scientist Wolfgang Peti pioneers using powerful magnets to study enzymes
At minus 459.67 degrees Fahrenheit—absolute zero—all motion, even the swirling of atoms, stops cold. Just a few degrees above that is the sweet spot for a machine that Wolfgang Peti, PhD, hopes will help unravel the biological basis of diabetes. He’s an expert in a research technique called nuclear magnetic resonance (NMR) spectroscopy, which depends on a powerful magnet that works only at frigid extremes. Early this year, Peti, an associate professor of medical science and chemistry at Brown University, received a cool $1.6 million Pathway to Stop Diabetes award from the American Diabetes Association (ADA) to bring this advanced scientific tool to the fight against diabetes.
Peti, who was born in Austria, has wanted to be a scientist ever since he was a boy. “I liked math, chemistry, and physics,” he says. “That’s the most fun I had.” NMR requires a solid understanding of all those topics and lured Peti to the field. For most of his career, Peti has applied NMR to the study of enzymes, the hardworking proteins that speed chemical reactions in the body. The body contains around 20,000 different proteins, some of which orchestrate the complex maneuvers that maintain blood glucose levels. For example, when blood glucose increases after eating, enzymes in the pancreas recognize the rise and tell pancreatic cells to release insulin. The insulin travels throughout the body, interacting with specific enzymes here and there, and acting as a signal for cells to absorb and store the excess blood glucose.
Studying diabetes-related enzymes with NMR is possible because the core of each atom behaves like a tiny magnet. Enzymes are microscopic collections of interconnected atoms, mostly carbon, nitrogen, oxygen, and hydrogen. The magnetic properties of each atom depend on its surroundings. By exerting a strong magnetic field on an enzyme, NMR can tease out an atom’s magnetic properties and thus its environment, allowing researchers to reconstruct what the enzyme looks like and how it works. Knowing an enzyme’s structure and function can help scientists develop new medications that target a particular enzyme, either blocking it from doing harm or helping it do some good in the body. Peti has solved the structure of more than 25 proteins with NMR so far, but he’s just getting started.
The Hard Part
Asked what the most challenging aspect of his research is, Peti doesn’t hesitate: It’s making the enzyme sample. Enzymes for NMR experiments are built in the laboratory. Peti says it can take his lab over four years to figure out how to make a new enzyme.
They start with genes, which are nature’s instruction manual. Genes tell an organism how to produce proteins. To make an enzyme sample in the lab, scientists insert a gene for the particular enzyme into a willing organism host—usually bacteria, but sometimes yeast, insect, or mammalian cells. To produce one type of enzyme, the scientists need to optimize the host, temperature, incubation time (which can be weeks long), pH, purification strategy, and dozens of other variables. Constructing another enzyme may involve a completely different process. This is part of what makes Peti’s lab special—it is the only lab in the world that has figured out how to produce certain enzymes.
In addition to the normal enzyme-growing pains, Peti must also clear some NMR-related hurdles. To make an NMR sample, scientists sometimes have to “label” it with costly atoms that have a desirable magnetic profile. For example, to look at the nitrogen atoms in an enzyme with NMR, they have to use a rare extra-heavy version of nitrogen. Some samples need multiple labels, while others need to be grown in D20, a heavy version of water. This can make an NMR sample very expensive (see “The Cost of Doing Science,” below).
Without the Pathway grant, Peti would not have been able to afford to pay such close attention to diabetes. “It’s very hard to change your direction,” he says, but the ADA funding gave him the opportunity to do diabetes research. Peti remembers getting the phone call that he’d won the grant just before Christmas. “I was very happy,” he says, as obtaining funding for basic science is often difficult at best. “It made my Christmas very relaxed, and I was excited to get the research started.”
Wolfgang Peti, PhD, will use the funds from the ADA Pathway award to bring his NMR prowess to diabetes science. “My grandmother did have diabetes, but quite frankly we all know people that have diabetes,” says Peti. His research team plans to do “whatever we need to get an answer,” enlisting additional scientific methods as necessary, such as X-ray crystallography. But NMR is where Peti feels most at home, and the method will offer a unique perspective on three emerging areas of diabetes research.
Communication between enzymes helps keep many biological processes running smoothly. Some interact with other enzymes by stripping them of phosphate chemicals, a biological equivalent of purse snatching. Peti studies an enzyme that removes phosphates from around 100 other enzymes. One helps turn glycogen, a glucose storage molecule, into glucose. If you could prevent activating this enzyme, then “you would have less glucose in your blood,” says Peti. The challenge is to do this without interfering with the 99 other enzymes, avoiding unwanted side effects. Peti and his team are using NMR to understand exactly how the phosphate-removal enzyme recognizes the glucose-releasing enzyme. Then they could design a drug to specifically block that interaction, lowering blood glucose while leaving all the other enzymes alone.
A second avenue of diabetes research Peti is pursuing with the Pathway grant involves the insulin receptor, a protein that recognizes insulin and tells a cell to absorb glucose from the blood. Certain genetic mutations to the insulin receptor are unusually common in people who have very long life spans (around 100 years or so). In fruit flies, these same mutations can also prolong life. Studying the mutations is aided by NMR. Peti hopes to explain how these mutations increase life span.
Wiggle, Wiggle, Wiggle
In another research project, Peti studies how a recently discovered inhibitor—a chemical that binds to and turns off certain enzymes—may help insulin work better in the body. Many medications are inhibitors that fight disease by blocking harmful enzymes. Peti’s inhibitor blocks an enzyme that shuts down the insulin receptor. Without an active insulin receptor, insulin’s voice is silenced—a common factor in type 2 diabetes. “No one had any idea how [the inhibitor] works,” he says, because it binds to a flexible region of the harmful enzyme. Most research techniques are blind to flexible protein parts, but NMR can detect protein jiggles. Peti’s team is using NMR to map out the interaction between the inhibitor and the flexible insulin-signaling enzyme. Once they understand how the inhibitor hangs on to the floppy enzyme and blocks it, Peti hopes they’ll be able to develop new diabetes medications that keep the insulin receptor, and insulin’s voice, at full volume.
The Cost of Doing Science
Research is an expensive endeavor. Here are some numbers from Wolfgang Peti’s laboratory. These represent only some of his expenses.
$7 per hour: Rate to use the NMR machine, which comes to $1,200 per week. NMR experiments can take hours or days, with the machine in almost constant use.
$500 to $1,500: Typical cost of producing one NMR protein sample.
$2.9 million: List price for the larger of the two NMRs owned by Brown University.
Brrr: Why Is the Magnet So Cold?
The magnet inside the NMR machine is actually just a coil of wire. The electrical current running through the wire generates a magnetic field. To produce a very strong magnetic field, researchers need to eliminate electrical resistance inside the wire. That’s accomplished by putting the wire inside jackets of liquid helium and nitrogen at extremely low temperatures.