A picosecond-resolution crystallographic

movie of a functioning protein has been created by a multinational collaboration. Crystallographers have amassed snapshots of thousands of frozen proteins, but those structure determinations provide only limited information on how a protein actually works. It would be more informative to capture a protein’s full collection of motions as it functions (see the article by Eric Galburt and Barry Stoddard in Physics Today, July 2001, page 33 ). Now, using the European Synchrotron Radiation Facility in Grenoble, France, researchers have made picosecond movies of a mutant form of myoglobin—the protein that stores oxygen in muscle tissue—ridding itself of a toxic carbon monoxide molecule. To capture this process, the scientists first hit the protein with a 1-ps pulse of laser light to dislodge the CO, then used an intense 150-ps x-ray pulse with a variable time delay. A CCD camera recorded the diffraction pattern at each time delay; from that recording, the collaborators deduced the sequence of the rapid structural changes. The movie showed the CO migrating to various sites in the protein, with the myoglobin rearranging its shape accordingly. The picosecond time scale of the structural changes is similar to the time scale of many molecular dynamics simulations, and could allow for closer comparison between theory and experiment. (F. Schotte et al., Science 300 , 1944, 2003 http://dx.doi.org/10.1126/science.1078797 )