National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)
P41GM136508
United States
Department of Defense (DOD, United States)
HDTRA1-21-1-0004
United States
Howard Hughes Medical Institute (HHMI)
United States
Citation
Journal: bioRxiv / Year: 2024 Title: Energy filtering enables macromolecular MicroED data at sub-atomic resolution. Authors: Max T B Clabbers / Johan Hattne / Michael W Martynowycz / Tamir Gonen / Abstract: High resolution information is important for accurate structure modelling. However, this level of detail is typically difficult to attain in macromolecular crystallography because the diffracted ...High resolution information is important for accurate structure modelling. However, this level of detail is typically difficult to attain in macromolecular crystallography because the diffracted intensities rapidly fade with increasing resolution. The problem cannot be circumvented by increasing the fluence as this leads to detrimental radiation damage. Previously, we demonstrated that high quality MicroED data can be obtained at low flux conditions using electron counting with direct electron detectors. The improved sensitivity and accuracy of these detectors essentially eliminate the read-out noise, such that the measurement of faint high-resolution reflections is limited by other sources of noise. Inelastic scattering is a major contributor of such noise, increasing background counts and broadening diffraction spots. Here, we demonstrate that a substantial improvement in signal-to-noise ratio can be achieved using an energy filter to largely remove the inelastically scattered electrons. This strategy resulted in sub-atomic resolution MicroED data from proteinase K crystals, enabling accurate structure modelling and the visualization of detailed features. Interestingly, filtering out the noise revealed diffuse scattering phenomena that can hold additional structural information. Our findings suggest that combining energy filtering and electron counting can provide more accurate measurements at higher resolution, providing better insights into protein function and facilitating more precise model refinement.
ProteinaseK / Endopeptidase K / Tritirachium alkaline proteinase
Mass: 28958.791 Da / Num. of mol.: 1 Source method: isolated from a genetically manipulated source Source: (gene. exp.) Parengyodontium album (fungus) / Gene: PROK / Production host: Parengyodontium album (fungus) / References: UniProt: P06873, peptidase K
Cryogen: NITROGEN / Specimen holder model: FEI TITAN KRIOS AUTOGRID HOLDER / Temperature (max): 90 K / Temperature (min): 77 K
Image recording
Average exposure time: 1 sec. / Electron dose: 0.002 e/Å2 / Film or detector model: FEI FALCON IV (4k x 4k) / Num. of diffraction images: 420 / Num. of grids imaged: 1 / Num. of real images: 1
EM imaging optics
Energyfilter name: TFS Selectris / Energyfilter slit width: 10 eV
Image scans
Sampling size: 14 µm / Width: 4096 / Height: 4096
EM diffraction
Camera length: 1402 mm
EM diffraction shell
Resolution: 1.09→56.82 Å / Fourier space coverage: 97.5 % / Multiplicity: 28.5 / Num. of structure factors: 98228 / Phase residual: 16.04 °
EM diffraction stats
Fourier space coverage: 97.5 % / High resolution: 1.09 Å / Num. of intensities measured: 2811895 / Num. of structure factors: 98228 / Phase error rejection criteria: None / Rmerge: 28.4
Reflection
Biso Wilson estimate: 8.76 Å2
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Processing
EM software
ID
Name
Version
Category
1
SerialEM
4.2.0
imageacquisition
6
Coot
0.9.8.93
modelfitting
8
PHASER
2.8.3
molecularreplacement
10
XDS
BUILT=20230630
symmetrydetermination
11
XSCALE
BUILT=20230630
crystallographymerging
12
phenix.refine
1.21.1
3Dreconstruction
19
PHENIX
1.21.1
modelrefinement
EM 3D crystal entity
∠α: 90 ° / ∠β: 90 ° / ∠γ: 90 ° / A: 66.92 Å / B: 66.92 Å / C: 107.56 Å / Space group name: P43212 / Space group num: 96
CTF correction
Type: NONE
3D reconstruction
Resolution: 1.09 Å / Resolution method: DIFFRACTION PATTERN/LAYERLINES / Symmetry type: 3D CRYSTAL
Atomic model building
B value: 11.29 / Protocol: OTHER / Space: RECIPROCAL / Target criteria: Maximum likelihood