Due to strong interaction of electrons with matter, 3D electron diffraction tomography has been proven to be a reliable method to solve structures of very small crystals, compared to X-ray diffraction; even for small protein crystals [1]. 

Several procedures for automated acquisition of tomographic diffraction data sets have been described [2, 3], using precession technique or discrete beam tilt perpendicular to the goniometer tilt axis. However, those mentioned methods are mainly used for less beam sensitive materials and are not suitable for low dose applications.

Shi et al. [4-7] refined the collection of 3D data sets under low dose condition (less than 10 e^–/Ų). Here, the camera system is continuously acquiring diffraction data during a continuous tilt of the goniometer. This allows to completely scan the Fourier space. It turned out that the stability of the goniometer tilt speed and the limited flexibility of the tilt acquisition parameters are problematic.

Here, we present a newly developed automatic data acquisition system, combining real-time direct control of the TEM-deflection systems, the goniometer tilt and the acquisition of high-resolution diffraction patterns with a synchronized CMOS camera. This can be realized by the TVIPS Universal Scan Generator (USG), controlling eight TEM deflection coils, i. e. four beam deflection coils and four image deflection coils.

For a static goniometer alpha, the total beam tilt range (±3° to ±5°, depending on the TEM) can be fragmented by a defined beam tilt range, e.g. 0.5° (see Fig. 1). During the camera exposure time the beam is continuously tilted for this defined range (e.g. 0.5°). The continuous beam sweep during exposure time ensures the complete sampling of the Fourier space. 

Several crystal structures (Carbamazepin: C₁₅H₁₂N₂O, bismuth oxychloride: BiOCl, Mayenite: Ca₁₂Al₁₄O₃₃) have been successfully solved by this method. The total acquisition time for 190 high resolution (1Å resolution) diffraction patterns is about 15 minutes, with a total electron dose of about 10 e^–/Ų. The collected 3D electron diffraction data sets were processed using the EDT-PROCESS software [8].

References

1.       J. A. Rodriguez, M. I. Ivanova, M. R. Sawaya, D. Cascio, F. E. Reyes, D. Shi,S. Sangwan, E. L. Guenther, L. M. Johnson, M. Zhang, L. Jiang, M. A. Arbing, B. Nannenga, J. Hattne, J. Whitelegge, A. S.     Brewster, M. Messerschmidt, S. Boutet, N. K. Sauter, T.Gonen and D. Eisenberg: Structure of the toxic core of α-synuclein from invisible crystals, Nature (2015);  525 (7570).

2.       U. Kolb, T. Gorelik, C. Kübel, M.T. Otten and D. Hubert: Towards automated diffraction Tomography: part I- data acquisition, Ultramicroscopy (2007) ; 107(6-7):507-13.

3.       D. Zhang, P. Oleynikov, S. Hovmoller and X. Zou:Collecting 3D electron diffraction data by the rotation method, Z. Kristallogr (2010); 225 94–102.

4.       D. Shi, B.L. Nannenga, M.G. Iadanza and T. Gonen: Three-dimensional electron crystallography of protein microcrystals, eLife (2013); 2:e01345.

5.       B.L. Nannenga, D. Shi, j. Hattne, F.E. Reyes and T. Gonen: Structure of catalase determined by MicroED, eLife (2014); 3:e03600.

6.       B.L. Nannenga and T. Gonen:Protein structure determination by MicroED, Current Opinion in Structural Biology (2014); Volume 27:24–31.

7.       B.L. Nannenga, D. Shi, A.G.W. Leslie and T. Gonen: High-resolution structure determination by continuous-rotation data collection in MicroED, Nature Methods 11(2014); 927–930.

8.     M. Gemmi, P. Oleynikov: Scanning reciprocal space for solving unknown structures: energy filtered diffraction tomography and rotation diffraction tomography methods. Z. für Krist. 228 (2013) 51-58.

Figures:

Schematic visualizing of the newly developed data acquisition system: combining real-time direct control of the TEM-deflection systems, the goniometer tilt and the acquisition of high-resolution diffraction patterns with a synchronized CMOS camera.

Diffraction pattern of Mayenite using beam sweeping method acquired by a TemCam-F416 mounted on a Tecnai-F12.

Projection of 3D volumetric data (209 frames of 0.5° sweeping range, 5 minutes total acquisition time, 9 ē/Å2 total electron dose) of Mayenite in reciprocal space.

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