Zhong and his team took laser snapshots of a single myoglobin protein -- the protein that carries oxygen inside muscle tissue -- immersed in water in the laboratory. They were able to measure how fast the water molecules were moving around the protein, and see how those movements related to characteristics of the protein at that moment -- the electrical charge at a particular site, for instance, or changes in the protein's shape.
Proteins can execute a movement in a few billionths of a second. Water normally moves a thousand times faster -- on the scale of a trillionth of a second. In previous work, the Ohio State researchers showed that water molecules slow down substantially as they gets close to a protein.
This new study shows that the water molecules slow even more once they reach the protein. The water forms a very thin layer -- only three molecules thick -- around the protein, and this layer is key to maintaining the protein's structure and flexibility, lubricating its movements.
Their findings challenge the conventional wisdom of theorists who try to envision what is happening on these tiny scales. Because they can't directly see what's happening, scientists use simulations to fill the gap.
The simulation software has improved in recent years, Zhong said. But for two years his team has compared simulations to actual experiments, and found that the two don't match up.
We are pretty confident at this point that the simulations need to change, Zhong said. Our experimental data provide a benchmark for testing and improving them.
In the future, Zhong's team will study how water affects proteins interacting with each other, and with DNA.
Our ultimate goal is to understand why water is so unique and important to life, he said.
|Contact: Dongping Zhong|
Ohio State University