Slowly pulling proteins apart reveals unexpected path to stability

From Duke University:

DURHAM, N.C. — Proteins are long strings of amino acids jumbled together like earphones left inside of a pocket for too long. But while a protein’s mess of intertwined knots may look haphazard, their specific folds are extremely important to their biological functions. Misfolded proteins are thought to be the genesis of diseases such as Alzheimer’s, Parkinson’s, Huntington’s and cystic fibrosis, just to name a few.

To get a detailed look at how different proteins are folded, researchers freeze them in a crystalline structure and bombard them with extremely short bursts of x-rays. By recording how the x-rays bounce off the samples, scientists can reconstruct the different shapes–or conformations–that a protein can take. They then use a variety of techniques to determine how the proteins fold themselves into their final structures.

But there are limits to these techniques that have caused most studies to focus on smaller, simpler proteins. The average protein found within a human cell, however, is neither small nor simple. Most are more like an economy-sized box of Christmas lights that have haven’t been opened in a decade.

In a new study, researchers at Duke University have taken a different approach to studying the conformations of one of these larger proteins. By slowly pulling apart a protein called Protein S, they discovered a previously unknown stable conformation made possible by a little help from its best friend.

The results, to be published in the September 9, 2016 issue of the Journal of Biological Chemistry (online on July 4, 2016), show that biochemists need to start rethinking some of their assumptions.

“Our study shows that some of our field’s long-held ideas need to be revised,” said Piotr Marszalek, professor of mechanical engineering and materials science at Duke. “Previous assumptions that were made about large proteins showing a lack of structure or stability might …

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