Seeing Alzheimer's amyloids(been unable to obtain crystals from fibr...)

Date:5/12/2008

been unable to obtain crystals from fibrils of full-length polypeptide chains. Structural models based on NMR data have also come up short. Scientists have made do with studying fragments of the A-beta peptide. The major barrier to determining the structure of A-beta fibrils is that the same peptide will exasperatingly assemble differently from fibril to fibrilunlike normal proteins, which reliably fold up the same way every time.

Grigorieff and his colleagues overcame this barrier by generating fibrils in a test tube under conditions that reduce the variability between fibrils, and by selecting about 200 images of fibrils that were most similar to each other and averaging them on a computer.

An expert at high resolution electron cryo-microscopy of protein complexes and macromolecular machines, Grigorieff said his lab made an image of the A-beta fibril at a resolution of eight Angstroms, revealing useful detail at a magnification of roughly a million times. Short of atomic resolution by a factor of 2.5 to 3, the image revealed how the peptide, a series of linked amino acids, was arranged in the tape-like fibril.

The next step will be a 3-D image that tells us exactly where all the amino acids are, postulates Grigorieff. This will tell us more about the chemical and biological properties of A-beta fibrils that we need to know to understand their role in Alzheimers.

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Contact: Laura Gardner gardner@brandeis.edu 781-736-4204 Brandeis University Source:Eurekalert

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