Saturday, August 02, 2008

First X-ray diffraction image of a single virus

Virus x-ray

X-ray crystallography has been a workhorse technique for chemists since the 1940s and 50s. For many years, it was the only way to determine the 3D structure of complex biological molecules such haemoglobin, DNA and insulin. Many a Nobel prize has been won poring over diffraction images with a magnifying glass.

But x-ray crystallography has a severe limitation: it only works with molecules that form into crystals and that turns out to be a tiny fraction of the proteins that make up living things.

So for many years scientists have searched in vain for a technique that can image single molecules in 3D with the resolution, utility and cost-effectiveness of x-ray diffraction.

That search might now be over. Today, John Miao at the University of California, Los Angeles, makes the claim that he and his team have taken the first picture of a single unstained virus using a technique called x-ray diffraction microscopy. Until now this kind of imaging has only been done with micrometre-sized objects.

Miao’s improvement comes from taking a diffraction pattern of the virus and then subtracting the diffraction pattern of its surroundings. The resolution of his images is a mere 22 nanometres, that’s an improvement of three orders of magnitude.

If confirmed, that’s an extraordinary breakthrough. With brighter x-ray sources, the team says higher resolution images will be possible and that it’s just a matter of time before they start teasing apart the 3D structures of the many proteins that have eluded biologists to date.

But best of all, x-ray diffraction gear is so cheap that this kind of technique should be within reach of almost any university lab in the world.

Ref: Quantitative Imaging of Single, Unstained Viruses with Coherent X-rays

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