How To Salvage Rejected X-ray Crystallography Data

During their quests for biomolecule structures, X-ray crystallographers toss out data that’s useful after all, two independent teams contend in the journal Science. They report strategies for using traditionally ignored information to improve structures’ quality. When solving an unfamiliar protein’s structure, crystallographers obtain phase information to interpret X-ray diffraction patterns. For that task, they normally employ heavy atoms, such as selenium, but this isn’t always straightforward. For four different proteins, Qun Liu of the New York Structural Biology Center, Wayne A. Hendrickson of Columbia University, and colleagues combined data from multiple crystals, demonstrating that typically neglected information in a protein’s own sulfur atoms provides phase assistance with no heavy atoms needed (DOI: 10.1126/science.1218753). P. Andrew Karplus of Oregon State University and Kay Diederichs of the University of Konstanz, Germany, developed a statistical quantity called CC*. Compared with established criteria, CC* better tells researchers at what point the outer edges of diffraction patterns should be cut from calculations, the authors say (DOI: 10.1126/science.1218231). Pattern edges give the highest resolution information about atomic positions but can get clouded by noise, a tough trade-off that the authors suggest CC* resolves.