X-ray Pulses Yield Biological Structures

Femtosecond X-ray pulses can produce high-quality diffraction data from both nanocrystalline and noncrystalline biomolecules, reports an international team of researchers experimenting at the new Linac Coherent Light Source at SLAC National Accelerator Laboratory, in Menlo Park, Calif. In theory, the ultrashort, intense X-ray bursts should enable researchers to extract structural information from a stream of small crystals or entities such as viruses or cells that have been difficult to examine using other techniques. The research team, led by Henry N. Chapman of Germany’s Center for Free-Electron Laser Science and Janos Hajdu of Sweden’s Uppsala University, worked on two such systems. In one study, the researchers used X-ray pulses to look at nanocrystals of the protein photosystem I (Nature, DOI: 10.1038/nature09750). The resulting protein structure matched one previously determined by conventional X-ray crystallography. A second study looked at mimivirus, the largest known virus (Nature, DOI: 10.1038/nature 09748). The mimivirus capsid is covered with fibrils that prevent crystallization. The X-ray data show that the capsid has icosahedral symmetry and an inhomogeneous core.