By G.P. Thomas
An International team of researchers including those from the physics, chemistry and biochemistry departments at the Arizona State University have devised a new nanocrystallography technique to capture three-dimensional images of biological molecules ensconced in protein nanocrystals.
Details of the new imaging technique will be presented at the American Crystallographic Association (ACA) meeting scheduled to be held in Boston, Massachusetts from 28 July to 1 August, 2012.
Conventional crystallography involves interaction of a beam of x-rays with a crystal. The density of electrons in the crystal is then determined by patterns of dark and light diffraction spots appearing on a photo detector. The pattern provides information on chemical bonds and three-dimensional position of atoms. The crystal is frozen to minimize radiation damage and is mounted on a rotating axis and subjected to X-ray beams. Freezing crystals prevents the study of molecules in their natural state. In order to facilitate this, the international team of researchers sent a beam of micron-sized droplets of protein nanocrystals streaming in a single file in vacuum across the X-ray beam. The X-ray beam was from the Linac Coherence Light Source (LCLS) at the SLAC National Accelerator Laboratory in Menlo Park. To quickly image the molecules before they are damaged by the laser beam, the scientists fired brief bursts of laser light measuring 100 times per second and detected the scattering pattern of each particle before they were destroyed. The numerous snapshots were then pieced together to obtain three-dimensional models of the molecules. One such molecule that was studied is the Photosystem 1-ferredoxin that drives photosynthesis in plants. The molecules were excited with green laser light to replicate the effect of sunlight falling on a leaf before capturing the X-ray image.