Presentation on theme: "Resolution Assessment in CryoEM Kristin Shingler Friday, August 2 nd, 2013."— Presentation transcript:
Resolution Assessment in CryoEM Kristin Shingler Friday, August 2 nd, 2013
What is Resolution? In short, how close two objects can be without appearing as one. Atomic resolution is achieved in x-ray crystallography. Typically, cryoEM generates sub-nanometer resolution, but recent reconstructions have approached atomic resolution.
Semliki Forest Virus 1986 3.2 nanometer r esolution Vogel et al., 1986 Nature
Sub-nanometer Resolution Hepatitis B Capsid, 9.1Å Resolution Conway et al., 1997 Science
Atomic Resolution Human Adenovirus 5, 3.6Å Resolution Liu et al., 2010 Science
What does resolution really mean? Zhou, Current Opinions in Structural Biology, 2008
What does resolution really mean? Baker et al., Methods in Enzymology, 2010
Resolution Assessment in X-ray Crystallography Modified Figure 5 from Wlodawer et al. 2007 Determined by how closely the crystal lattice can be packed, while still maintaining diffraction Various statistical measurements correlate the resolution
3D Reconstruction Work Flow Baker, Olson, and Fuller 1999 Microbiology and Molecular Biology Reviews
Fourier Shell Correlation F 1 – Structure Factor for Map #1 F 2 – Structure Factor for Map #2 r i – individual voxel element r – radius “measures the normliazed cross-correlation coefficient between two 3D volumes as a function of spatial frequency” - van Heel
Conventional Resolution Estimation versus Gold Standard ConventionalGold Standard Model Even Map Odd Map FSC and Resolution Estimate Model ½ Data Map ½ Data Map FSC and Resolution Estimate
Conventional Resolution Estimation versus Gold Standard Scheres and Chene, 2012 Nature Methods
Why this paper? Elife is an open access journal It provides readers with both the reviewers comments AND the author’s response to reviewers An excellent example of high quality work showing the disparity between conventional and gold standard resolution assessment
Timeline of Events The authors first reported the resolution of their map to be 4.6Å by using conventional resolution assessment This method was challenged by reviewers The authors reassessed resolution using the gold standard method and found the map was 5.3Å resolution
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