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Biotech Science

First X-Ray Diffraction Image of a Single Virus 57

KentuckyFC writes "X-ray crystallography has been a workhorse for chemists since the 1940s and 50s, revealing the 3D structure of complex biological molecules such as haemoglobin, DNA and insulin. But the technique 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. But today, a team of US researchers say they have created the first image of a single uncrystallized virus using x-ray diffraction. The trick is to take a diffraction pattern of the virus and then subtract the diffraction pattern of its surroundings (abstract). The breakthrough paves the way for scientists to start teasing apart the 3D structures of the many proteins that have eluded biologists to date."
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First X-Ray Diffraction Image of a Single Virus

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  • Makes sense (Score:1, Interesting)

    by clonan ( 64380 ) on Friday June 20, 2008 @12:08PM (#23874353)

    If you look at the density of a protein (which is pretty much all of a virus) it looks like a crystal. The common high school idea of a protein as a drop of fatty amino acids surrounded but wet amino acids is very false.

    I wonder when they will start imaging other proteins?

    This could be a boon to proteinomics!

  • by blueg3 ( 192743 ) on Friday June 20, 2008 @12:56PM (#23875081)

    While the statement "you cannot focus X-rays like you can visible light with lenses" is misleading, it's true. You can't focus X-rays like you can focus visible light, and you can't do it (effectively) with lenses. However, you can focus X-rays.

  • by clonan ( 64380 ) on Friday June 20, 2008 @03:49PM (#23877675)

    Actually refolding is fairly rare and almost always results from an environmental change (the protein get shoved into a membrane or it is surrounded by chaperon proteins). There are hinges and the like which affect functionality but thoes are very specific domains typically including a proline which isn't really an amino acid. Whole sale spontaneous refolding is essentially unheard of.

    I went to a public high school and an engineering college. I heard the oil-drop model of proteins until I took biochem as a junior in college. The Biochem I took was actually a graduate level course.

  • by Anonymous Coward on Saturday June 21, 2008 @12:09AM (#23882195)

    This is actually a very important point. The limiting factor in pretty much any coherent diffractive imaging (CDI) experiment is the angle to which one can measure scattering. This angle depends strongly on the wavelength of the light and the size of the detector: shorter wavelengths and larger detectors get you better potential resolution.

    Whether or not you can measure scattering to the highest possible angle is often another question entirely. In particular, for biological specimens, there appears to be a pretty fundamental limit on how much energy you can deposit in the sample before it, for lack of a better term, blows up. That's why papers of this ilk usually rely on the supposition that one can measure 100,000 or more such patterns and combine them to form a very high resolution data set (or at least a reconstruction that's consistent with all the data).

    CDI's a pretty new field and some of us think it has a lot of promise; however, it should be pointed out that for something like a virus, one might well be better off with a TEM. There you could probably get better than 1 nm resolution on a 100 nm thick sample. Of course, with TEM the resolution becomes poorer as the sample thickness increases, so like traditional X-ray microscopy, CDI probably has a more credible application in cellular imaging.

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