Scientists have for the first time mapped the atomic structure of a protein within a living cell. The technique, which peered into cells with an X-ray laser, could allow scientists to explore some components of living cells as never before. "This is a new way to look inside cells," said David S Eisenberg, a biochemistry professor at University of California, Los Angeles, and Howard Hughes Medical Institute investigator. "There are a lot of semi-ordered materials in cells where an X-ray laser could provide powerful information," Eisenberg added. They include arrays in white blood cells that help to fight parasites and infections, insulin-containing structures in the pancreas and structures that break fatty acids and other molecules into smaller units to release energy. The research was conducted at the US Department of Energy's SLAC National Accelerator Laboratory. In the experiment at SLAC's Linac Coherent Light Source X-ray laser, researchers probed a soil-dwelling bacterium, Bacillus thuringiensis or Bt, that is commonly used as a natural insecticide. Strains of this bacterium produce microscopic protein crystals and spores that kill insects. Normally scientists need to find ways to crystallise proteins in order to get their structures - typically a time-consuming, hit-and-miss process - but these naturally occurring crystals eliminated that step. A liquid solution containing the living cells was jetted into the path of the ultrabright LCLS X-ray laser pulses. When a laser pulse struck a crystal, it created a pattern of diffracted X-ray light.
More than 30,000 of these patterns were combined and analysed by sophisticated software to reproduce the detailed 3-D structure of the protein. Many of the bacterial cells likely ruptured and spewed their crystal contents as they flew at high speed toward the X-rays. But because it took just thousandths of a second for the cells to reach the X-ray pulses, it's very likely that many of the X-ray images showed protein crystals that were still inside the cells, the researchers concluded. The research was published in the journal Proceedings of the National Academy of Sciences.