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![[Figure 2]](rr5162fig2mag.jpg)
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Figure 2
Plot of average structure-factor amplitude against resolution to aid the selection of the optimal blurring/sharpening B value, as shown in the CCP-EM GUI (Burnley et al., 2017  ). The data correspond to a cryo-EM reconstruction of β-galactosidase (PDB entry 5a1a, EMDB entry EMD-2084; Bartesaghi et al., 2015). Different levels of map blurring and sharpening are shown, using an array of B values from −100 Å (blurring) to +100 Å (sharpening) in increments of 20 Å. For the optimally blurred/sharpened map, the average amplitude should decay to zero at the `high-resolution limit' (above which the data contain no information about the true structure). For high levels of map sharpening, the average amplitude persistently increases with resolution: this indicates over-sharpening. For high levels of map blurring, the average amplitude approaches zero rapidly prior to reaching the high-resolution limit, resulting in a loss of high-resolution information. In this case, the optimal average level of blurring over the map is around 40 Å (subjectively determined by manual inspection of the plot), in agreement with the maps shown in Figs. 1 and 3. |
![[Figure 2]](rr5162fig2.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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