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SLAC Snapshot

February 3, 2011 - 5:02pm

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The LCLS Atomic, Molecular and Optical instrument hutch where experiments were performed | Photo courtesy of Brad Plummer

The LCLS Atomic, Molecular and Optical instrument hutch where experiments were performed | Photo courtesy of Brad Plummer

“Say cheese!” Millions of Americans are likely to be saying that this weekend, and not just those cheering on the Packers this weekend (take them by three).

After all, Super Bowl parties are a great place to take pictures, especially if your team happens to be winning. But it’s tough to take great pictures of a crowd that’s constantly moving. It’s even harder if you’ve got extra-hyper toddlers or extra-squirmy pets. So rather than apply a straightjacket (which don’t show up so well on Facebook posts or holiday pictures), many people solve the problem by taking a lot of snapshots, and trying to take them really fast.

In a sense, that’s what researchers at the Office of Sciences’ Stanford Linear Accelerator Laboratory (SLAC) recently did with proteins and viruses. Proteins and viruses probably couldn’t match a puppy for sheer squirminess, but they are extremely tiny, which makes it tough to take their snapshots. Yet it’s important to do so because the structure of viruses and proteins is often related to how they function.

To take their ‘snapshots,’ researchers at the Department of Energy’s Stanford Linear Accelerator (SLAC), which is managed by the Office of Science, used the world’s first hard X-ray free-electron laser – the Linac Coherent Light Source – to blast laser light at viruses and protein nanocrystals in extremely short pulses (a few millionths of a billionth of a second long). The strobe-like bursts were so short that the ‘picture’ was taken before the sample exploded. Well, it’s not EXACTLY a picture. Before the sample is destroyed, x-rays from the beam bounce off the sample in all directions, to be sensed by sophisticated detectors. By looking at a series of many upon many of these “diffraction patterns,” scientists can reconstruct the actual structure of the sample. That’s how scientists were able to assemble a composite picture of the protein, using 10,000 of the 3 million snapshots taken.

The protein SLAC scientists took a picture of was called Photosystem I, which converts sunlight to energy during photosynthesis. It is also among a specialized class of proteins called membrane proteins. Membrane proteins serve as a bridge between the inside and the outside of cells, which makes them important for both diseases trying to infect them and the drugs devised to fight them. These proteins are also exceptionally difficult to image – scientists can spend years trying to get them to sit still for a snapshot through the process of crystallization. Because of those difficulties, scientists have determined the structures of only a handful of the estimated 30,000 human membrane proteins, even though they are targets of more than 50 percent of the medicines on the market.

Taking pictures of viruses in motion is also extremely difficult. The press release announcing that SLAC scientists had taken snapshots of the Mimivirus noted, “biologists have long dreamed of making images of viruses, whole microbes and living cells without freezing slicing or otherwise disturbing them,” gives a sense of the difficulties involved.

By taking these snapshots, SLAC researchers have shown a potential way to save years of research, and perhaps speed up the process to new cures. So with that flashy future in mind, put on a big smile and just “Say ch- !”

For more information on the Office of Science, please go to: http://www.science.doe.gov/.

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