The Structural Architecture of an Infectious Mammalian Prion Using Electron Cryomicroscopy
Fig 5
Single particle averaging of GPI-anchorless PrP 27–30 fibril images.
(A) Average from 1072 fibril segments (top left) and the logarithm of their summed power spectrum (bottom left). The arrowhead indicates the characteristic 4.8 Å cross-β signal. Representative 2D class average of 100 single protofilaments (top right) and their averaged Fourier-transform (bottom right). Single and double arrows are pointing to intensities at 19.1 Å (single pixel) and ~40 Å (38.3 Å and 44.6 Å pixels), respectively. (B) Gallery of 2D class averages obtained from reference-free analysis of individual protofilaments. Box size is 150 by 150 pixels, equivalent to 20.1 by 20.1 nm. (C) Histogram of manually determined sizes of densities along the protofilament from the class averages in (B). The majority of densities fall into the classes between 15 and 25 Å. (D) The average over all amplitude spectra of all class averages. A plot of the meridian of the Fourier-transform (red line) reveals a broad peak around 40.2 Å and a smaller peak at 20.1 Å (arrows). The Nyquist frequency (2.68 Å) corresponds with the 75 pixel outer border of the spectra. Scale bars, 10 nm.