SNS researchers overcome freezing sample problem in biostudies

SNS researchers overcome freezing sample problem in biostudies

9:50 AM, 22nd September 2012
SNS researchers overcome freezing sample problem in biostudies
Eugene Mamontov, lead instrument scientist at the Spallation Neutron Source's Backscattering Spectrometer, has developed a method to study biological samples at supercold temperatures.

OAK RIDGE, US: Researchers at the Spallation Neutron Source BASIS beam line at the Department of Energy’s Oak Ridge National Laboratory have successfully developed a method to study biomolecules (proteins) at temperatures far below freezing using a lithium chloride preparation in the aqueous solvent that prevents freezing.

Studying biosamples at supercold temperatures - 200 Kelvin - was previously impossible, as the water in such a solution inevitably freezes and with it, the biosample’s dynamic interactions freeze, too. The ability to study proteins at these temperatures gives researchers an important new avenue for understanding how they function in living organisms.

Neutron researchers need to study the dynamic interaction of proteins and their aqueous solvent at low temperatures to understand their vibrational behaviour at the atomic level. Then, while slowly raising the temperature to physiological conditions, they can study the unique biological “relaxational” motions that dominate as the temperature is raised.

Now Eugene Mamontov, Lead Instrument Scientist at the SNS’s Backscattering Spectrometer (BASIS) and Xiang-qiang Chu, his Postdoc, have successfully navigated the research roadblock with a unique method that stops the hydrated biomolecule from freezing.

Mamontov and Chu had already shown that a lithium chloride aqueous solution is remarkably similar in its dynamics to pure water and it does not freeze at very low temperatures. With the assistance of Hugh O’Neill and Qiu Zhang of the Biology and Soft Matter Division in ORNL’s Neutron Sciences Directorate, they mixed an aqueous solution of lithium chloride with protein, producing a slurry with bulk-like water inside.

“You look at it and you can’t tell the difference between the solution and pure water. You measure the dynamics. There is very little difference. Yet, unlike water, the stuff does not freeze down to about 200 Kelvin. It changes to a thick, glassy consistency; however it remains water-like,” explained Mamontov. “The protein kind of floats, moving inside the solvent (which is mostly water) - a much more realistic portrayal of proteins in living cells,” added Mamontov.

In a recent paper, they successfully studied the dynamics of the protein at many different temperatures in a realistic aqueous environment, without freezing. Proteins at temperatures as low as liquid helium or nitrogen behave essentially like atoms in any regular solid. But, when warmed, in addition to vibrating, explained Mamontov, “They start to do something else. They start to make relaxational motions. Think of tentacles, or some kind of mop with which you sweep the floor.”

Mamontov said the BASIS instrument is uniquely suited to study the problem. Unlike other spectrometers, BASIS can separately and simultaneously measure both the activity of the solvated protein and the aqueous solution that surrounds it.

“It is important to an understanding of life. It is fundamentally important to biological science. We need to know how the protein conforms, how it responds to the changing temperature of its solvent, in order to understand how a protein functions inside us,” said Mamontov.

The neutron scattering experiments at Oak Ridge National Laboratory’s (ORNL) Spallation Neutron Source were sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.

© Oak Ridge National Laboratory News

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