Biological single-particle imaging using XFELs - towards the next resolution revolution.

Dominik Oberthür

doi:10.1107/s2052252518015129

Abstract

Better injectors resulting from careful iterative optimization used at high repetition XFELs in combination with better detectors and further developed algorithms might, in the not so distant future, result in a 'resolution revolution' in SPI, enabling the molecular and atomic imaging of the dynamics of biological macromolecules without the need to freeze or crystallize the sample.

Highlights

While SFX resulted in new structures (Colletier et al, 2016; Kang et al, 2015; Redecke et al, 2013) that could not be obtained from crystallography at room temperature, and both revived and revolutionized time-resolved crystallography (Nogly et al, 2018; Olmos et al, 2018; Pande et al, 2016), the initial results from biological single-particle imaging (SPI) (Seibert et al, 2011; Ekeberg et al, 2016) showed that the X-ray intensity from XFELs, the available detectors, and techniques to introduce the sample into the focused X-ray sampling position, were all insufficient to obtain (near) atomic resolution structural information from biological macromolecules
While SFX resulted in new structures (Colletier et al, 2016; Kang et al, 2015; Redecke et al, 2013) that could not be obtained from crystallography at room temperature, and both revived and revolutionized time-resolved crystallography (Nogly et al, 2018; Olmos et al, 2018; Pande et al, 2016), the initial results from biological single-particle imaging (SPI) (Seibert et al, 2011; Ekeberg et al, 2016) showed that the X-ray intensity from XFELs, the available detectors, and techniques to introduce the sample into the focused X-ray sampling position, were all insufficient to obtain atomic resolution structural information from biological macromolecules
Other problems are rather specific to the nature of the generic SPI experiment: the number of X-ray pulses delivered by the FEL per second, the intensity of each pulse, shot-to-shot variations in pulse intensity and X-ray energy, sample delivery, the nature of the sample and associated radiation damage effects, and even the background noise/ scatter introduced from various sources, all remain challenges in FEL experiments

Summary

Introduction

While SFX resulted in new structures (Colletier et al, 2016; Kang et al, 2015; Redecke et al, 2013) that could not be obtained from crystallography at room temperature, and both revived and revolutionized time-resolved crystallography (Nogly et al, 2018; Olmos et al, 2018; Pande et al, 2016), the initial results from biological SPI (Seibert et al, 2011; Ekeberg et al, 2016) showed that the X-ray intensity from XFELs, the available detectors, and techniques to introduce the sample into the focused X-ray sampling position, were all insufficient to obtain (near) atomic resolution structural information from biological macromolecules. At the same time as the first SPI experiments were carried out, the ‘resolution revolution’ in cryo transmission electron microscopy (cryoEM) (Subramaniam et al, 2016) became evident, achieving the goal of near atomic resolution single-particle imaging.

Results

Conclusion