Researchers map iron transport protein

The paper, which will appear in the Proceedings of the National Academy of Sciences, details the work of Associate Professor Martin Lawrence and doctoral candidate Anoop Sendamarai. The pair have spent the past two years studying Steap3, a protein involved in regulating the body’s absorption of iron.

The results of their studies – the first three-dimensional maps of the atoms that make up Steap3 – could allow pharmaceutical companies to someday design drugs to regulate iron levels in the blood.

“Iron is essential,” Lawrence said. “You can’t live without it, but it’s a double-edged sword. Too much of a good thing can kill you.”

Iron serves several important functions in the bloodstream. It carries oxygen, transports electrons within cells and plays an important role in enzyme systems.

Iron irregularities are some of the most common blood disorders in the world. According to the World Health Organization, iron deficiency, which can lead to anemia, affects more than a billion people around the world and can cause developmental and immune system problems.

Conversely, having too much iron, a condition called hemochromatosis, can also hurt the body by releasing destructive free radicals, Lawrence said. Hemochromatosis affects about one in every 300 people and is most common in people of northern European ancestry. Left untreated, it can lead to early death, often by age 50.

“We’re struck by how many people have too much or too little iron,” Lawrence said.

To understand Steap3’s role in transporting and maintaining balanced levels of iron, Lawrence and Sendamarai first had find and purify samples of the protein and then turn those samples into crystals.

Lawrence said the result of the crystallization process, if done correctly, is analogous to the rigid structure of a brick wall. If done incorrectly, it more closely resembles a pile of bricks.

“It’s kind of a black art really more than a science,” Lawrence said. “You can’t always predict the kind of witch’s brew that needs to be around to get it to crystallize.”

He said only a handful of labs in the country are crystallizing iron transport proteins like Steap3, a fact that places MSU on the same shelf as places like Harvard Medical School.

Once crystallized, the samples are shot with a powerful X-ray beam. Electrons in the sample diffract the X-rays, creating patterns on a digital sensor. The technique, called X-ray crystallography, has been used since the 1950s to de-termine the structure of different substances.

In their basement lab in the campus’s New Chemistry Building, Lawrence and Sendamarai then examined the diffraction patterns created by Steap3.

“It’s kind of like a contour map,” Sendamarai said. “Whenever we see the peaks, we know there are atoms.”

Working backward, they can mathematically determine the position of atoms in the protein and display them in three dimensions.

The computer-drawn result, a three-dimensional image that resembles tangled ribbons and strings, is an picture of what the atoms of Steap3 look like.

Sendamarai said having that picture, which depicts all the nooks and crannies on the protein’s surface, could allow drug companies to design drugs to fit those spots like puzzle pieces.

If a future drug fits those nooks just right, it could help treat hemochroma-tosis. From there, Sendamarai said it would be conceivable to work backward and possibly treat iron deficiencies or anemia.

Lawrence said that Steap3 is only one in a family of proteins that affect iron transport. This summer, in addition to continuing to study Steap3, Lawrence and Sendamarai hope to learn whether the lab will receive a grant from the National Institutes of Health to work on other iron transport proteins.

“It’s a critical step towards toward learning to modulate iron levels in pa-tients with too much or too little iron,” Sendamarai said. “But, there are a lot of question marks left in iron transport. It’s a big field.”

Source: Montana State University