FEL Reveals Detailed Architecture of Proteins

A novel free-electron laser (FEL) x-ray technique that obtains high-resolution structural insight into biomolecules can deliver structural data that could be used to design tailor-made medications.

Understanding the structure of biomolecules is important for the fields of medicine and biology because their shape often determines their function. These structures are commonly determined by x-ray crystallography, but this process is often difficult and slow, and the failure rate is high.

Schematic representation of the experimental setup at the Coherent X-ray Imaging end station at the Linac Coherent Light Source. Millions of tiny crystals are injected into the free-electron laser beam in a thin liquid jet. Diffraction patterns are generated when a crystal intersects a free-electron x-ray flash and are captured on a detector shown on the left. (Images: MPI for Medical Research)

Now, scientists from Max Planck Advanced Study Group and Max Planck Institute for Medical Research have used the Linac Coherent Light Source (LCLS) in California to determine the structure of the small protein lysozyme — the first enzyme ever to have its structure revealed — down to a resolution of 0.19 nm. Ten thousand snapshot exposures from crystals measuring only one-thousandth of a millimeter were collated; the data was comparable to that obtained using traditional approaches and lysozyme crystals that are one hundredfold larger. No signs of radiation damage were found.

“We were able to show that atomic resolution information can be collected before radiation damage has a chance to take effect,” said Anton Barty, co-author and DESY scientist. “The key is ultrashort pulses — we see no effects of damage before the x-ray pulse has already passed.”

“The good agreement benchmarks the method, making it a valuable tool for systems that yield only tiny crystals,” said Ilme Schlichting of Max Planck Institute for Medical Research.

Structure of the protein lysozyme. The spatial arrangement of the 129 amino acids is schematically depicted in the form of spirals (helices) and arrows (pleated sheets).

Using the LCLS enables scientists to study previously intractable molecular structures. This is because the x-ray flashes from the laser are extremely bright, so only the tiniest crystals are needed for a structural analysis. The microcrystals used in this study almost vaporized immediately when subjected to the intense x-ray light.

“The exceptionally intense x-ray pulses possible with FELs open the door for analyzing completely new classes of biomolecules like proteins from the cell membrane, that are hard or nearly impossible to crystallize,” said Henry Chapman of the German accelerator center DESY. “This will allow us to explore uncharted terrain in structural biology.”

The study appeared in Science.

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