Proteins bring order into the water

New findings about protein folding

Water molecules dance around a protein (green) © idw - Ruhr-Universität Bochum
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It is especially the type of folding that determines their function in proteins - a dynamic process that runs very fast. In examining this "dance" of proteins so far one has ignored the partner: the water. Researchers have now observed this interplay between water and proteins using terahertz spectroscopy. For the first time, they were able to show that proteins influence the movements of the surrounding water network over large areas.

About 1, 000 molecules of water are "brought into line" by a protein. If they move as disorganized as a group of discodancers without protein, they tend to go to a minuet dance near a protein, according to the researchers in the current issue of Proceedings of the National Academy of Science PNAS.

Forgot dance partner

Until now, the focus of investigations on protein folding has been exclusively on the movements of the protein scaffold and the side chains. "It is believed, however, that the rapid movements of water, and in particular their coupling with protein movement, play an important role in protein folding and hence function, " explains Professor Martina Havenith-Newen of Ruhr-Universität Bochum (RUB), who was involved in the new study with colleagues from Illinois and Nevada. Fundamental questions that have so far remained unanswered: How far does the influence of proteins last? Do the fast water movements change when two proteins approach each other?

Absorption of terahertz radiation allows conclusions

The development of powerful laser sources in the terahertz (THz) range opens up completely new possibilities for research: depending on its state, water absorbs terahertz radiation in a characteristic way - thus making conclusions possible. For example, while at 370 Kelvin (97 ° C), only 0.7 percent of the radiation (at a frequency of approximately 1.5 THz) penetrates a 100-micron thick water layer, it is already 40 at 270 Kelvin (-3 ° C) Percent. So ice is much more transparent to terahertz radiation than water.

The reason for this lies in the tiny, fast vibrations in which networks of water molecules are constantly located. They last less than a picosecond (one trillionth of a second) and are determined by a striving of the water molecules away from each other and the rotations against each other. Frozen water absorbs the radiation at a different frequency than liquid water. Each measurement in the THz range is therefore characteristic of the state of the water. display

Minuet instead of disco

The researchers now took advantage of the fact that the vibrations of water networks are changing not only by the temperature, but also by the proximity of proteins.

"It can be imagined so that a protein brings the water molecules in its environment into a certain orderly movement, " explains Havenith-Newen. The movement of the uninfluenced water resembles the dance of discotheques, there are loose ties to the next partner, which break after a time. Water near protein dances more like a minuet. The movement is more coordinated, and binding to the next partner lasts longer. The result is that water near the body releases less THz radiation. This phenomenon makes it possible to directly observe the effects of proteins on water. The researchers conclude from the amount of absorbed radiation back to the state of the water.

Far-reaching influence

"Using our measurements, we were able to show for the first time that proteins influence the fast movements of the water network over large areas, " explains the chemist. Around 1, 000 water molecules are affected by a protein in their network movements. Such a far-reaching effect, which can be measured up to a distance of 15 to 20 angstroms (1 = one tenth of a nanometer), was predicted in simulations but could not be observed experimentally.

With the help of the new measurements, it was shown that the influence extends well beyond the range in which static changes of the structure, such as local density changes, can be observed (~ 3 )., "In the long term, it remains to be seen what role the terahertz dance of water plays with the protein for its biological function, " notes Havenith-Newen.

(idw - Ruhr-University Bochum, 19.12.2007 - DLO)