PT  - JOURNAL ARTICLE
AU  - Martynowycz, Michael W.
AU  - Clabbers, Max T.B.
AU  - Hattne, Johan
AU  - Gonen, Tamir
TI  - Ab initio phasing macromolecular structures using electron-counted MicroED data
AID  - 10.1101/2021.10.16.464672
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.10.16.464672
4099  - http://biorxiv.org/content/early/2021/10/17/2021.10.16.464672.short
4100  - http://biorxiv.org/content/early/2021/10/17/2021.10.16.464672.full
AB  - Structures of two globular proteins were determined ab initio using microcrystal electron diffraction (MicroED) data that was collected on a direct electron detector in counting mode. Microcrystals were identified using a scanning electron microscope (SEM) and thinned with a focused ion-beam (FIB) to produce crystalline lamellae of ideal thickness. Continuous rotation data were collected using an ultra-low exposure rate on a Falcon 4 direct electron detector in electron-counting mode. For the first sample, triclinic lysozyme extending to 0.87 Å resolution, an ideal helical fragment of only three alanine residues provided initial phases. These phases were improved using density modification, allowing the entire atomic structure to be built automatically. A similar approach was successful on a second macromolecular sample, proteinase K, which is much larger and diffracted to a modest 1.5 Å resolution. These results demonstrate that macromolecules can be determined to sub-Ångström resolution by MicroED and that ab initio phasing can be successfully applied to counting data collected on a direct electron detector.Competing Interest StatementThe authors have declared no competing interest.