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X-ray laser lights up small wonders

Thomas White (DESY)

A three-dimensional rendering of X-ray data obtained from over 15,000 single nanocrystal diffraction snapshots recorded at the Linac Coherent Light Source, the world's first hard X-ray free-electron laser, located at SLAC National Accelerator Laboratory. The 3-D structure of proteins -- in this case Photosystem I -- can be determined from these diffraction patterns. Each nanocrystal was destroyed by the intense X-ray pulse, but not before information about its structure was revealed.

Scientists are using intense, ultra-short X-ray pulses from a free-electron laser to collect data on the 3-D structure of proteins and single-shot images of an intact virus.

The feat demonstrates a way to use X-rays "to look at very, very small objects with really high resolution," Michael Bogan, a staff scientist at the Department of Energy's SLAC National Accelerator Laboratory, told me today.

The proof-of-concept studies using the world's first hard X-ray free-electron laser — the Linac Coherent Light Source, located at the lab — were published in this week's issue of the journal Nature.


The research was led by Henry Chapman of the Center for Free Electron Laser Science at the German national laboratory DESY and Janos Hajdu of Sweden's Uppsala University, together with a team of more than 80 researchers, including Bogan, from 21 institutions.

"The LCLS beam is a billion times brighter than previous X-ray sources, and so intense it can cut through steel," Chapman said in a news release. "Yet these incredible X-ray bursts are used with surgical, microscopic precision and exquisite control, and this is opening whole new realms of scientific possibilities."

The technique opens up pathways that could lead to new drugs designed to target specific proteins,  to new views of the internal structure of viruses, or to new insights into why plants are so efficient at converting sunlight into energy.

Diffraction before destruction
Until now, making X-ray images of such tiny objects was difficult because conventional X-rays destroyed the object being imaged before any useful structural data was recorded.

The hard X-ray free-electron laser gets around this problem by shooting femtosecond-long pulses at the object. A femtosecond is one-quadrillionth of a second. Think a few millionths of a billionth of a second long. "And they are coming in so quickly that the X-rays scatter off that object and we capture them on a camera — and then the object explodes," Bogan explained.

This concept is known as "diffraction before destruction," he said.

Since the objects are destroyed soon after they are hit by the laser, to create the images, researchers send streams of the objects into the path of the X-ray beam.

Protein structure
In the protein structure experiment, the team targeted Photosystem I, a protein found in the membrane of plant cells that plays a key role in converting sunlight into energy.

To make the image of the protein's structure, they squirted millions of nanocrystals containing copies of Photosystem I in a liquid jet 10 times thinner than a hair across the X-ray beam. The laser pulses hit the crystals at various angles and scattered into the detector, forming the patterns needed to reconstitute the images.

The team then combined 10,000 of the 3 million snapshots into the known molecular structure of Photosystem I. In a few weeks, a second round of the experiment will use even shorter pulses, potentially allowing the team to get "single-atom resolution of these membrane structures. This will be really, really, really incredible," Bogan said.

Some researchers will use the technology to understand the structure of proteins that they want to target with new drugs, he noted. The Department of Energy has, well, energy on its mind.

"We're trying to understand how these Photosystem membrane proteins can actually convert the sun's light into energy, and so the next targets are to start looking at other proteins involved in this process such as Photosystem II, which is another unsolved membrane protein," Bogan said.

If researchers can understand how plants convert sunlight into energy so efficiently, they may be able to reverse-engineer the process, he added. "Just having the basic understanding of how this is working would be tremendously useful."

Amoeba virus
For the virus experiment, the researchers sprayed an aerosol stream of virus particles into the beam, allowing them to make single-shot portraits of the Mimivirus, the world's largest known virus, which infects amoebas.

The images show the 20-sided structure of the virus' outer coat and an area of denser material inside, which may represent genetic material. The team speculates that shorter, brighter pulses focused to a smaller area should improve the resolution of the images to reveal details as small as a nanometer.

"This is a brand new way to look at a biological object," team member Jean-Michel Claverie, director of the Structural & Genomic Information Lab in Marseille, said in a news release. "This will allow us address not only questions related to the internal structure of the virus, but its intrinsic variability from one individual virus particle to the next — a microscopic variability that might play a fundamental role in evolution."

Bogan noted that the realm of research opened up by this new imaging technique is just now becoming apparent. He likened it to being handed a computer that is more than a billion times faster than what's currently available.

"You couldn't even imagine what you would be able to do with this thing because it would be so powerful," he told me. "And that's really where we are right now. We are at the very beginning of this capability, and these are the first demonstrations of the type of biological experiments we'll be doing with them."

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John Roach is a contributing writer for msnbc.com. Connect with the Cosmic Log community by hitting the "like" button on the Cosmic Log Facebook page or following msnbc.com's science editor, Alan Boyle, on Twitter (@b0yle).