Scientists learn to predict protein-stabilizing ability of small molecules

’Osmolytes’ critical to survival of kidney cells and organisms in extreme environments

Researchers at the University of Texas Medical Branch at Galveston (UTMB) have developed a new way to predict the ability of certain small molecules to protect proteins in the cells of a wide variety of organisms living in extreme environments. The technique, described in a paper published online Oct. 7 in the Proceedings of the Natural Academy of Sciences (PNAS), is a method of calculating the stabilizing effect on cellular proteins by small organic molecules called “osmolytes.” It could have implications for the study of Alzheimer’s disease, cystic fibrosis, kidney disease and stabilizing protein drugs.

Osmolytes, whose effects were first well described in 1982, work to preserve various forms of life under extraordinarily hostile conditions. They keep cells alive in human kidneys, for example, despite high concentrations of the protein-destroying chemical urea; they enable a species of frog found in the Arctic literally to be frozen solid and then thawed without harm; and they make it possible for the remarkable microscopic creatures known as “water bears” to survive complete drying, exposure to intense radiation, and temperatures ranging from a few degrees above absolute zero to that of superheated steam.

In the PNAS paper, Matthew Auton and D. Wayne Bolen describe their application of thermodynamic calculations to successfully predict the ability of a variety of osmolytes to protect proteins in cells under stress. Proteins function as molecular machines, performing tasks essential for cellular survival; extremes of heat and cold and changes in the chemical environment around the cell can cause the proteins to lose their proper shape and prevent them from functioning properly. Osmolytes, however, are able to force proteins to take on the correct shape and stay on the job.

“You can think of protein structure as origami, like strips of paper folded up into unique structures,” said Bolen, senior author on the paper and a professor of human biological chemistry and genetics at UTMB. “Understanding how and why they fold or unfold — they’re not very stable, and there’s this constant pressure on them to unfold — is a major goal of biomedical science. What we’ve done is shown that we can calculate how osmolytes will influence the stability of different proteins, and we’ve also determined how different parts of the proteins interact with the osmolytes, which can give us significant insights on the protein-folding process.”

Protein folding and unfolding, Bolen said, are critical features of disorders like Alzheimer’s disease, mad cow disease and cystic fibrosis. Osmolytes perform vital functions in many different locations in the human body, notably the kidneys and the brain. “Without osmolytes, the kidneys wouldn’t function at all, and brain tissue wouldn’t be able to be as resilient as it is,” Bolen said. “Medicine has only really emphasized their role in the kidneys, but they also occur in a lot of other tissues, and this technique should be quite useful for medical researchers looking at osmolytes throughout the body.”