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Abstract
A sample of purified Syrian hamster PrP27–30 prion fibers was analyzed by synchrotron small-angle X-ray scattering (SAXS). The SAXS pattern obtained was fitted to a model based on infinitely long cylinders with a log-normal intensity distribution, a hard-sphere structure factor and a general Porod term for larger aggregates. The diameter calculated for the cylinders determined from the fit was 11.0 ± 0.2 nm. This measurement offers an estimation of the diameter of PrPSc fibers in suspension, i.e., free of errors derived from estimations based on 2D projections in transmission electron microscopy images, subjected to further possible distortions from the negative stain. This diameter, which corresponds to a maximum diameter of approximately 5.5 nm for each of the two intertwined protofilaments making up the fibers, rules out the possibility that PrPSc conforms to a stack of in-register, single-rung flat PrPSc monomers; rather, PrPSc subunits must necessarily coil, most likely several times, into themselves.
Disclosure of Potential Conflicts of Interest
No potential conflicts of interest were disclosed.
Acknowledgments
This study was supported by grants FOOD-CT-2006-023183 (STRAINBARRIER) and FP7 222887 (PRIORITY) from the European Union, and BFU2006-04588/BMC from the Spanish Ministry of Science and Education.