Terahertz spectroscopy provides a window on protein-water rearrangements during the folding process, such as breaking protein-water-hydrogen bonds and replacing them with protein-protein-hydrogen bonds, Gruebele said. The remaking of hydrogen bonds helps organize the structure of a protein.
In tests on ubiquitin, a common protein in cells, the researchers found that water molecules bound to the protein changed to a native-type arrangement much faster than the protein. The water motion helped establish the correct configuration, making it much easier for the protein to fold.
"Water can be viewed as a 'designer fluid' in living cells," Gruebele said. "Our experiments showed that the volume of active water was about the same size as that of the protein."
The diameter of a single water molecule is about 3 angstroms (an angstrom is about one hundred-millionth of a centimeter), while that of a typical protein is about 30 angstroms. Although the average protein has only 10 times the diameter of a water molecule, it has 1,000 times the volume. Larger proteins can have hundreds of thousands times the volume. A single protein can therefore affect, and be influenced by, thousands of water molecules.
"We previously thought proteins would affect only those water molecules directly stuck to them," Gruebele said. "Now we know proteins will affect a volume of water comparable to their own. That's pretty amazing."
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| Contact: James E. Kloeppel kloeppel@illinois.edu 217-244-1073 University of Illinois at Urbana-Champaign Source:Eurekalert |