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Scientists Develop New Color-coded Test For Protein Folding

Date:
April 14, 2005
Source:
Stanford University
Summary:
Every protein is folded into a unique, three-dimensional shape that allows it to function properly. Now Stanford University scientists have developed a simple test that instantly changes color when a protein molecule attached to a gold nanoparticle folds or unfolds.
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Stanford chemist Richard Zare and his colleagues have developed a simple test for determining when protein molecules change shape. The researchers created a solution of gold nanoparticles coated with the protein cytochrome c. Lowering the pH from 10 to 4 caused the cytochrome c molecules to unfold and the particles to aggregate, turning the solution from red to blue. The technique may one day provide biomedical researchers a fast, affordable method for detecting antibodies and other disease-related proteins.
Credit: Photo Matthew R. Hammond/Stanford University

Every protein is folded into a unique, three-dimensional shape that allows it to function properly. Now Stanford University scientists have developed a simple test that instantly changes color when a protein molecule attached to a gold nanoparticle folds or unfolds. The new technique, which works on the same principle as ordinary pH tests that measure the acidity of water, is described in the March 2005 issue of the journal Chemistry and Biology.

"What we've developed is a simple and inexpensive sensor for determining when a protein changes its conformation," said study co-author Richard N. Zare, the Marguerite Blake Wilbur Professor in Natural Science in Stanford's Department of Chemistry. According to Zare, the new sensor may eventually provide biomedical researchers a fast, affordable method for detecting antibodies and other disease-related proteins.

Acid and base

In their experiment, Zare, postdoctoral fellow Soonwoo Chah and graduate student Matthew R. Hammond created a liquid solution containing nano-sized particles of gold saturated with a protein called cytochrome c.

"We chose gold nanoparticles because they are simple to prepare, easy to control and cost effective," the authors wrote. "To the best of our knowledge, however, gold nanoparticles have not been previously used to investigate the folding and unfolding of proteins."

The initial batch of gold-cytochrome solution had a rosy red hue and a pH value of 10—about the same as an over-the-counter heartburn medication. But when drops of hydrochloric acid were added, the solution began to change color, turning purple when the pH reached 5.8 and light blue at pH 4, which is close to the acidity of wine.

Lab analysis revealed that additional hydrochloric acid was causing the cytochrome c molecules to unfold. As a result, gold nanoparticles coated with cytochrome c began clumping together—a process that caused the solution to quickly change from red to blue as the acidity increased.

The researchers were surprised to discover that, when the pH was raised from 4 to 10, the blue solution turned reddish once again—a strong indication that some cytochrome c molecules had refolded into their original three-dimensional shape. In fact, the experiment showed that, when attached to gold film, cytochrome c can fold, unfold and refold countless times depending on the acidity of the solution, thus making it an ideal tool for detecting conformational changes in proteins.

"While we're not ready to mass-produce this technology, we believe it will eventually be useful for testing other, more complicated proteins," Zare said, noting that a gold nanoparticle sensor could turn out to be a quick and inexpensive way for doctors to identify antibodies and other signs of infection in the blood stream. Over the next few months, he and his colleagues plan to re-do the experiment using other protein molecules.

The Chemistry and Biology study was supported by a grant from the National Science Foundation


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The above post is reprinted from materials provided by Stanford University. Note: Materials may be edited for content and length.


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Stanford University. "Scientists Develop New Color-coded Test For Protein Folding." ScienceDaily. ScienceDaily, 14 April 2005. <www.sciencedaily.com/releases/2005/03/050326010448.htm>.
Stanford University. (2005, April 14). Scientists Develop New Color-coded Test For Protein Folding. ScienceDaily. Retrieved August 4, 2015 from www.sciencedaily.com/releases/2005/03/050326010448.htm
Stanford University. "Scientists Develop New Color-coded Test For Protein Folding." ScienceDaily. www.sciencedaily.com/releases/2005/03/050326010448.htm (accessed August 4, 2015).

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