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Protein Movie Reveals Atomic Details
By Nancy Touchette

Scientists have captured real-time moving images of a protein in action in greater detail than ever seen before. Viewers can see the movement of individual atoms as a carbon monoxide molecule is let loose from a myoglobin protein.

X-ray crystallography reveals motion in myoglobin as carbon monoxide (center yellow circle) is swept away. View movie (952 kb)

“This is something I have dreamed about for a long time,” says Philip A. Anfinrud of the National Institutes of Health in Bethesda, Maryland, who participated in the recent study. “We can see the individual atoms and when they move and how they move. It’s pretty cool.”

Such moving images of proteins go a long way toward realizing the ultimate goals of human genome research. Understanding how proteins function in intimate detail is key to understanding how cells, tissues, and organs work together in a healthy human being.

Eventually, researchers would like to know how genetic mutations affect protein function so they can use the information to design new therapies.

“Imagine a steam locomotive displayed in a museum,” says Anfinrud. “How much more could you learn by going to a train station and watching them stoke up a fire, blow the whistle, and make it chug its way down the tracks?”

In the study, published in Science, the researchers used a laser to release a carbon monoxide molecule from its binding site in a mutated form of myoglobin. Myoglobin is a protein that delivers oxygen to muscles and removes carbon monoxide, which is toxic.

The movie was generated from a series of images acquired over intervals nearly as short as one 10-billionth of a second, using X-ray crystallography.

With this technique, researchers pulse an X-ray beam at a protein crystal—an ordered array of protein molecules. Electrons bouncing off the crystal are detected by a computer, forming patterns that researchers use to deduce the protein’s structure.

By piecing together the individual pictures, the researchers produced a movie of the motion inside the myoglobin protein as carbon monoxide was swept away. They were surprised to see movement far more dramatic than what they had predicted from static models of the protein.

A train in motion provides significantly more information about how it works than a static model. And proteins are not much different, says Anfinrud.

“When we are able to look at a protein and rationally alter its structure to change its behavior, we can become real engineers of biology,” he says.

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F. Schotte et al. Watching a protein as it functions with 150-ps time-resolved X-ray crystallography. Science 300, 1944-1947 (June 20, 2003).

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