Aug 8 – 10, 2019
Flatiron Institute
America/New_York timezone

Non-Uniformity of Projection Distributions Attenuates Resolution in Cryo-EM

Aug 8, 2019, 5:15 PM
2h
Ingrid Daubechies Auditorium (Flatiron Institute)

Ingrid Daubechies Auditorium

Flatiron Institute

162 Fifth Ave, 2nd fl. New York, NY 10010

Speaker

Dr Philip Baldwin (The Salk Institute)

Description

Virtually every single-particle cryo-EM experiment currently suffers from specimen adherence to the air-water interface, leading to a non-uniform distribution in the set of projection views. Non-uniform (anisotropic) distributions can negatively affect map quality, elongate structural features, and in some cases, prohibit interpretation altogether. Although some consequences of non-uniform sampling have been described qualitatively, we know little about how sampling quantitatively affects resolution in cryo-EM. Here, we show how inhomogeneity in any projection distribution scheme attenuates the global Fourier Shell Correlation (FSC) in relation to the number of particles and a single geometrical parameter, which we term the sampling compensation factor (SCF). The reciprocal of the SCF is defined as the average over Fourier shells of the reciprocal of the per-particle sampling and normalized to unity for uniform distributions. The SCF ranges from one to zero, with values close to the latter implying large regions of poorly sampled or completely missing data in Fourier space. Using two synthetic test cases, influenza hemagglutinin and human apoferritin, we demonstrate how any amount of sampling inhomogeneity always attenuates the FSC compared to a uniform distribution.

Primary author

Dr Philip Baldwin (The Salk Institute)

Co-author

Prof. Dmitry Lyumkis (The Salk Institute)

Presentation materials

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