Atomic structures determined from digitally defined nanocrystalline regions

Abstract

Nanocrystallography has transformed our ability to interrogate the atomic structures of proteins, peptides, organic molecules and materials. By probing atomic level details in ordered sub-10 nm regions of nanocrystals, approaches in scanning nanobeam electron diffraction extend the reach of nanocrystallography and mitigate the need for diffraction from large portions of one or more crystals. We now apply scanning nanobeam electron diffraction to determine atomic structures from digitally defined regions of beam-sensitive peptide nanocrystals. Using a direct electron detector, we record thousands of sparse diffraction patterns over multiple crystal orientations. We assign each pattern to a specific location on a single nanocrystal with axial, lateral and angular coordinates. This approach yields a collection of patterns that represent a tilt series across an angular wedge of reciprocal space: a scanning nanobeam diffraction tomogram. From this diffraction tomogram, we can digitally extract intensities from any desired region of a scan in real or diffraction space, exclusive of all other scanned points. Intensities from multiple regions of a crystal or from multiple crystals can be merged to increase data completeness and mitigate missing wedges. Merged intensities from digitally defined regions of two crystals of a segment from the OsPYL/RCAR5 protein produce fragment-based ab-initio solutions that can be refined to atomic resolution, analogous to structures determined by selected area electron diffraction. In allowing atomic structures to now be determined from digitally outlined regions of a nanocrystal, scanning nanobeam diffraction tomography breaks new ground in nanocrystallography.