This rendering shows a lysozyme structural model against its X-ray diffraction pattern from SLAC’s Linac Coherent Light Source (LCLS), a powerful X-ray laser facility. Researchers have achieved high-resolution images of these simple biomolecules using advanced crystallography at LCLS. This successful demonstration paves the way for studies of more complex biological structures. Image Credit: Anton Barty/DESY |
An international team led by the U.S.
Department of Energy’s (DOE) SLAC National Accelerator Laboratory has proved
how the world’s most powerful X-ray laser can assist in cracking the structures
of biomolecules, and in the processes helped to pioneer critical new investigative
avenues in biology.
The team’s experiments, reported in Science, used SLAC’s Linac Coherent
Light Source (LCLS) to obtain ultrahigh-resolution views of crystallized
biomolecules, including a small protein found in egg whites called lysozyme.
For decades, scientists have reconstructed
the shape of biological molecules and proteins by illuminating crystallized
samples with X-rays to study how they scatter the light. The team’s work
with lysozyme represents the first-ever high-resolution experiments using
serial femtosecond crystallography—the split-second imaging of tiny crystals
using ultrashort, ultrabright X-ray laser pulses (a femtosecond is one
quadrillionth of a second).
The technique used a higher resolution than
previously achieved using X-ray lasers, allowing scientists to use smaller
crystals than typical with other methods, and could also enable researchers to
view molecular dynamics in a way never before possible.
“We were able to actually visualize the
structure of the molecule at a resolution so high we start to infer the
position of individual atoms,” said Sébastien Boutet, a staff scientist at LCLS
who led the research.
“Not only that, but the structure we
observed matches the known structure of lysozyme and shows no significant sign
of radiation damage, despite the fact that the pulses completely destroy the
sample. This is the first high-resolution demonstration of the ‘diffraction-before-destruction’ technique on biological samples, where we’re
able to measure a sample before the powerful pulses of the LCLS damage it,” he
added.
The team chose lysozyme as the first sample
for their research because it is easy to crystallize and has been extensively
studied. Their work not only determined lysozyme’s structure at such high
resolution that it showed individual amino acids, but also proved the ability
to use extremely small crystals for a range of applications. Boutet says the
team has also studied more complex proteins and systems that they are analyzing
now.
Ultimately, scientists using LCLS are
driving toward an atomic- and molecular-scale understanding of complex
biological systems—such as the membrane proteins that are critical in cell
functions and the mechanisms that power photosynthesis—which could lead to
discoveries in a range of sciences, from pharmaceutical breakthroughs to new
sources of alternative energy.
The experiment was the first study
performed on the new Coherent X-ray Imaging (CXI) instrument, a “molecular
camera” designed, built, and commissioned by SLAC and now available to the
scientific community. Also key to the study was a novel custom-made detector,
the Cornell-SLAC Pixel Array Detector (CSPAD), developed in collaboration
between Cornell University and SLAC for use at the CXI
instrument.
“This
important demonstration shows that the technique works, and it paves the way
for a lot of exciting experiments to come,” says Boutet.
