In biology textbooks, proteins have long been cast as static molecules, but new research suggests that they are far more dynamiceven to the point of seeming fluid in their movements. Scientists from the University of Pennsylvania describe in a paper that will appear Thursday in Nature their work on the internal motions of the calmodulin-peptide protein complex. "Everything is moving, and it's moving all the time, very fast," lead author A. Joshua Ward says. "The really exciting thing is they [proteins] move so much that, potentially, it dramatically influences how they work. This is the beginning of a long new story that fundamentally will have a lot to do with understanding protein function."

The scientists exposed the protein to 13 different temperatures, ranging from 278 degrees to 346 degrees kelvin, and watched it squirm using nuclear magnetic resonance (NMR) relaxation imaging. Compared to earlier crystallographic studies, the NMR data revealed a much broader range of motion. "The beauty of this experimental study is that motion and temperature are inextricably linked, and by understanding how motion changes in response to temperature, you understand more about the motions themselves," says Andrew Lee, now at the University of North Carolina. "The common thinking has been that the structure of proteins dictates their functions and that each one has a different biochemical task. But they fluctuate ... and these fluctuations are also critical for protein activity."