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Figure 1
Left: FSC plots from the aberration experiments on aldolase and 20S proteasome at 200 keV. The top plot shows the half-set FSC and the bottom plot shows the FSC against maps calculated from the respective atomic models (PDB entries 1zah and 6bdf; see text for details). Note that estimating the aberrations during the initial CTF refinement already produces a significant increase in resolution (red line). It also allows more effective Bayesian polishing and defocus refinement, increasing the resolution further (solid black line). Neglecting the aberrations while keeping the remainder of the parameters the same (dashed black line) allows us to isolate the effects of aberration correction. For the proteasome, it also exposes a slight (false) positive peak in the half-set FSC around 2.7 Å which corresponds to a negative peak in the reference FSC. This indicates that the phases of the complex amplitudes of the 3D map are, on average, flipped at this frequency band owing to the strong aberrations. Right: small regions of the resulting maps illustrating the effect of considering the aberrations. The maps correspond to the solid black lines (aberrations considered) and the dashed black lines (aberrations not considered) in the FSC plots. The aldolase maps were sharpened by a B factor of −50 Å2 and contoured at 3.7σ. The proteasome maps were sharpened by a B factor of −55 Å2 and contoured at 3.5σ. All maps were rendered by PyMOL v.1.8.4.1.

IUCrJ
Volume 7| Part 2| March 2020| Pages 253-267
ISSN: 2052-2525
https://doi.org/10.1107/S2052252520000081