Atomic structures determined from digitally defined nanocrystalline regions.

Area of Science:

• Crystallography
• Electron Microscopy
• Structural Biology

Background:

• Nanocrystallography enables atomic structure determination of various molecules.
• Scanning nanobeam electron diffraction (SNED) probes atomic details in sub-10 nm regions.
• SNED can potentially eliminate the need for large crystal portions.

Purpose of the Study:

• To apply SNED for atomic structure determination of beam-sensitive peptide nanocrystals.
• To develop and validate scanning nanobeam diffraction tomography (SNDT).
• To demonstrate fragment-based ab initio structure solution and refinement using SNDT.

Main Methods:

• Utilizing a direct electron detector to record thousands of sparse diffraction patterns from multiple crystal orientations.
• Assigning each diffraction pattern to a specific location on a nanocrystal using coordinates.
• Constructing a scanning nanobeam diffraction tomogram representing a tilt series in reciprocal space.
• Digitally extracting intensities from specific regions within the tomogram.
• Merging intensities from multiple regions or crystals to improve data completeness.

Main Results:

• Atomic structures were determined from digitally defined regions of beam-sensitive peptide nanocrystals.
• Scanning nanobeam diffraction tomography was successfully applied.
• Fragment-based ab initio solutions were obtained from merged intensities of protein nanocrystal segments.
• These solutions were refined to atomic resolution, comparable to selected-area electron diffraction results.

Conclusions:

• Scanning nanobeam diffraction tomography allows atomic structure determination from digitally outlined regions of nanocrystals.
• This technique significantly advances the capabilities of nanocrystallography.
• SNDT opens new avenues for analyzing small or beam-sensitive crystalline samples.