Solving protein structure from sparse serial microcrystal diffraction data at a storage-ring synchrotron source

• Published in: IUCrJ Vol. 5; no. 5; pp. 548 - 558
• Main Authors: Lan, Ti-Yen, Wierman, Jennifer L., Tate, Mark W., Philipp, Hugh T., Martin-Garcia, Jose M., Zhu, Lan, Kissick, David, Fromme, Petra, Fischetti, Robert F., Liu, Wei, Elser, Veit, Gruner, Sol M.
• Format: Journal Article
• Language: English
• Published: England International Union of Crystallography 01.09.2018
• Subjects: Algorithms; Analysis; Crystal structure; Crystallography; Diffraction; EMC algorithm; Frames; Free electron lasers; Indexing; Laser beams; Methods; Microcrystals; NANOSCIENCE AND NANOTECHNOLOGY; protein microcrystallography; Protein structure; Proteins; Radiation damage; Research Papers; sparse data; storage-ring synchrotron sources; Synchrotron radiation sources; X-ray crystallography; X-ray serial microcrystallography; X-rays; X-ray serial microcrystallography; protein microcrystallography; EMC algorithm; sparse data; storage-ring synchrotron sources
• ISSN: 2052-2525; 2052-2525
• DOI: 10.1107/S205225251800903X

In recent years, the success of serial femtosecond crystallography and the paucity of beamtime at X-ray free-electron lasers have motivated the development of serial microcrystallography experiments at storage-ring synchrotron sources. However, especially at storage-ring sources, if a crystal is too small it will have suffered significant radiation damage before diffracting a sufficient number of X-rays into Bragg peaks for peak-indexing software to determine the crystal orientation. As a consequence, the data frames of small crystals often cannot be indexed and are discarded. Introduced here is a method based on the expand–maximize–compress (EMC) algorithm to solve protein structures, specifically from data frames for which indexing methods fail because too few X-rays are diffracted into Bragg peaks. The method is demonstrated on a real serial microcrystallography data set whose signals are too weak to be indexed by conventional methods. In spite of the daunting background scatter from the sample-delivery medium, it was still possible to solve the protein structure at 2.1 Å resolution. The ability of the EMC algorithm to analyze weak data frames will help to reduce sample consumption. It will also allow serial microcrystallography to be performed with crystals that are otherwise too small to be feasibly analyzed at storage-ring sources.