June 9, 2010 Three-dimensional imaging is dramatically expanding
the ability of researchers to examine biological specimens,
enabling a peek into their internal structures. And recent
advances in X-ray diffraction methods have helped extend the
limit of this approach. While significant progress has been made
in optical microscopy to break the diffraction barrier, such
techniques rely on fluorescent labeling technologies, which
prohibit the quantitative 3-D imaging of the entire contents of
cells. Cryo-electron microscopy can image structures at a
resolution of 3 to 5 nanometers, but this only works with thin
or sectioned specimens. And although X-ray protein
crystallography is currently the primary method used for
determining the 3-D structure of protein molecules, many
biological specimens -- such as whole cells, cellular
organelles, some viruses and many important protein molecules --
are difficult or impossible to crystallize, making their
structures inaccessible. Overcoming these limitations requires
the