Compiled by BioPhotonics staff
UPPSALA, Sweden – Imaging individual biological molecules using
even the most powerful microscopes has given scientists grief, but with the aid
of extremely intensive and ultrashort x-ray pulses from the first free-electron
laser, scientists now can capture images of viruses, membrane structures and single-cell
Paving the way for studies of biological structures at molecular
levels, an international research team from Uppsala University and the Swedish University
of Agricultural Sciences has captured an image of an intact virus and a membrane
structure from a photo-synthetic bacterium with the free-electron laser. The group’s
findings were published in two articles in the journal Nature, Feb. 3, 2011 (doi: 10.1038/nature09748
and doi: 10.1038/nature09750).
For years, biologists have dreamed of capturing images of viruses,
single-cell organisms and bacteria without having to section, freeze or mark them
with metals, a technique necessary for electron microscopy. The new findings now
make it possible.
The free-electron laser in the hard x-ray area – the Linac
Coherent Light Source – has a light intensity that can cut through steel.
A single pulse contains as much energy as all the sunlight hitting the Earth focused
on a square millimeter. Its light pulses are extremely short, ~50 to 70 fs, which
means that it can replicate an image of a micrometer-size virus before it is heated
up and destroyed.
X-ray diffraction, an instrument in identifying biological structures,
requires crystallized samples of sufficient size, which means that many particles
must be packed into crystals. For single particles, the x-ray dose must be increased
so much that the particle is destroyed. However, a few years ago it was suggested
that extremely short pulses from a free electron laser could create an image of
the particle before it was damaged. The method currently is being tested on biological
Studies have been conducted to test the method on Mimivirus, the
world’s largest known virus. Larger than some single-cell organisms and the
only virus that can be infected by a virus of its own, its size and special surface
structure could not be studied by conventional imaging methods. The team also has
proved that x-ray pulses can be used to study the structure of vitally important
membrane proteins, most notably the protein complex that captures sunlight and converts
it to energy in photosynthesizing organisms.
With the new methodology, scientists can – for the first
time – begin to piece the “blank patches” in structural biology
together to study at the level of the atom.