When Nicole Sampson ’85 was a student at HMC, she became annoyed at the cost of the chemical used to kill algae in her waterbed. Thus, when given the opportunity to design her own experiment in a chemistry class, Sampson decided to synthesize the algaecide herself.

“Then I understood why it was so expensive,” she said. “Harvey Mudd College developed in me the motivation to go out and discover things.”

As a professor of chemistry at Stony Brook University, part of the State University of New York, Sampson has made significant discoveries in the field of enzyme chemistry. Enzymes are biological catalysts. These proteins make reactions proceed faster without being used up in the process. In recognition of her work on two very different enzymes, cholesterol oxidase and triosephosphate isomerase, as well as a third protein fertilin-beta, Sampson recently received the 2005 American Chemical Society (ACS) Biological Chemistry Division’s Pfizer Award in Enzyme Chemistry. In 2001, she was honored with the Arthur C. Cope Scholar Award, also from ACS.

“I really like to try to understand at an almost mechanical level how things function,” Sampson said. “These molecules are so big that they have a lot of the mechanical about them.”

Cholesterol oxidase has been a target in Sampson’s lab ever since she joined  Stony Brook University 12 years ago. This protein isn’t naturally found in humans, only bacteria, which use it to obtain energy. However, it is used in the standard test to measure cholesterol in the blood. Before Sampson began her work, most of the information on cholesterol oxidase dealt with its use in cholesterol testing.

Cholesterol, a fat-soluble molecule, is a component of cell membranes. Cholesterol oxidase, on the other hand, is a water-soluble protein. Sampson determined from the structures where they should bind, but not how

they did so, given the difference in solubility. Thus, she developed probes to investigate how cholesterol and cholesterol oxidase bind.

This work has been challenging because the standard ways to determine enzyme rates and mechanisms don’t apply since cholesterol is part of the cell membrane. For example, researchers often change the concentration of a molecule and see how that affects the reaction. Changing the concentration of cholesterol in a membrane, however, changes the membrane’s structure, which also affects the rate of reaction. Sampson developed new techniques that are now used by other researchers studying membrane-bound proteins. She has also worked with Alice Vrielink, a researcher at the University of California, Santa Cruz, to obtain x-ray crystallography data on the proteins.

“We started the study for fundamental, interesting reasons, but it has turned out that there may be lots of applications in the agricultural and medical areas,” Sampson said.

Cholesterol oxidase has become more important in recent years since the agriculture company Monsanto discovered that it is an insecticide. When ingested by beetles, cholesterol oxidase catalyzes the conversion of cholesterol to cholest-4-en-3-one in the insects’ gut cells. Cholest-4-en-3-one has a very different shape than cholesterol, so it doesn’t fit in cell membranes as well. The weakened gut cell membranes eventually fall apart, killing the insect.

The enzyme also may be important in some diseases. Mycobacterium tuberculosis, which causes tuberculosis, replicates within human macrophages very large cells that engulf and absorb waste and foreign materials in the human body. M. tuberculosis may get out of macrophages by using cholesterol oxidase to weaken their membranes.

“If this turns out to be a critical path for M. tuberculosis to live in macrophages, then it’s a potential drug target,” Sampson said.

Tuberculosis strikes about 15,000 people in the United States each year, and many more around the world. The disease is difficult to treat because many strains of M. tuberculosis are multi-drug resistant; a therapy targeting cholesterol oxidase would be very different from previous treatments.

Sampson also studies the protein-protein interactions involved in sperm binding to an egg during fertilization. Her work focuses on a protein called fertilin-beta, which is part of the sperm’s cell membrane. Binding of fertilin-beta to its receptor on the egg usually sets off a cascade of reactions, including fusion of the sperm and egg and prevention of further sperm from fertilizing the egg.

Fertilin-beta is a large protein, but Sampson has focused on a particular sequence responsible for its activity of just three amino acids, which are the building blocks of proteins. Her laboratory has made synthetic forms of fertilin-beta that include this three-amino-acid sequence repeated many times. These molecules are effective inhibitors of fertilization in mouse eggs and are being used to identify the crucial receptor(s) on the egg.

This research has important applications both to people who want to become pregnant and those who do not. A drug that binds to the fertilin-beta receptor and stimulates the reactions that inhibit sperm from binding could be a powerful contraceptive, in part because it would be cell-specific, as opposed to today’s hormonal birth control. The interaction fertilin-beta and its receptor could also be a problem for infertile couples, and drugs could be developed to stimulate binding.

Sampson’s fertility research is challenging in part because eggs are in short supply. Unlike many other kinds of cells, eggs cannot be grown in vitro. One mouse supplies about 30 eggs. As such, the receptors with which the fertilin-beta interacts on the egg are difficult to isolate.

“Because eggs are in such limited quantities, lots of genetics have been done on this system. However, those experiments don’t give the same results as biochemical experiments,” Sampson said. “We want to resolve why the outcomes are so different.”

In addition to her research, Sampson also teaches organic chemistry and other courses at Stony Brook University. This semester she has 800 students. Sometimes she feels frustrated by the lack of faculty-student interaction she’s able to achieve,

especially compared to HMC.

“When I went to UC Berkeley for graduate school, I realized what a nurturing environment HMC had been,” Sampson said. “Yes, Mudd is a difficult school, there’s lots of work, but the amount of faculty interaction was phenomenal.”