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| Home > Publications database > Enhanced EMC—Advantages of partially known orientations in x-ray single particle imaging |
| Journal Article | PUBDB-2024-06703 |
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2024
American Institute of Physics
Melville, NY
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Please use a persistent id in citations: doi:10.1063/5.0188772 doi:10.3204/PUBDB-2024-06703
Abstract: Single particle imaging of proteins in the gas phase with x-ray free-electron lasers holds great potential to study fast protein dynamics, butis currently limited by weak and noisy data. A further challenge is to discover the proteins’ orientation as each protein is randomly orientedwhen exposed to x-rays. Algorithms such as the expand, maximize, and compress (EMC) exist that can solve the orientation problem andreconstruct the three-dimensional diffraction intensity space, given sufficient measurements. If information about orientation were known,for example, by using an electric field to orient the particles, the reconstruction would benefit and potentially reach better results. We usedsimulated diffraction experiments to test how the reconstructions from EMC improve with particles’ orientation to a preferred axis. Ourreconstructions converged to correct maps of the three-dimensional diffraction space with fewer measurements if biased orientation information was considered. Even for a moderate bias, there was still significant improvement. Biased orientations also substantially improvedthe results in the case of missing central information, in particular in the case of small datasets. The effects were even more significant whenadding a background with 50% the strength of the averaged diffraction signal photons to the diffraction patterns, sometimes reducing the datarequirement for convergence by a factor of 10. This demonstrates the usefulness of having biased orientation information in single particleimaging experiments, even for a weaker bias than what was previously known. This could be a key component in overcoming the problemswith background noise that currently plague these experiments.
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