Abstract

With recent developments in X-ray sources, instrumentation and data-analysis tools, time-resolved crystallographic experiments, which were originally the preserve of a few expert groups, are becoming simpler and can be carried out at more radiation sources, and are thus increasingly accessible to a growing user base. However, these experiments are just that: discrete experiments, not just `data collections'. As such, careful planning and consideration of potential pitfalls is required to enable a successful experiment. Here, some of the key factors that should be considered during the planning and execution of a time-resolved structural study are outlined, with a particular focus on synchrotron-based experiments.

Highlights

  • Macromolecular X-ray crystallography has become nearubiquitous at synchrotrons, which often house multiple heavily automated beamlines dedicated to macromolecular crystallography, permitting routine in-house and even remote data collection without extensive user training

  • Serial crystallography approaches at both X-ray free-electron lasers (XFELs) and synchrotrons generally encompass four types of sampledelivery methods, which include liquid-injection, microfluidics, fixed-target and hybrid approaches; these have recently been reviewed in detail (Martiel et al, 2019; Grunbein & Nass Kovacs, 2019)

  • gas dynamic virtual focusing nozzle (GDVN) injectors are well suited to XFEL experiments but are less ideal for synchrotron measurements, especially on monochromatic macromolecular crystallography (MX) beamlines

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Summary

Introduction

Macromolecular X-ray crystallography has become nearubiquitous at synchrotrons, which often house multiple heavily automated beamlines dedicated to macromolecular crystallography, permitting routine in-house and even remote data collection without extensive user training. D78, 14–29 research papers unravelling of biochemical mechanisms of proteins, for example via mutation studies, substrate analogues or freezetrapping techniques (Moffat, 2001) While these classical X-ray crystallographic approaches have been extremely powerful in obtaining insight into equilibrium-state structures, structures obtained from mutants, or with substrate analogues or inhibitors, have the potential to reflect artefacts that only exist in the mutant or particular ligand complex, when trying to probe a reaction mechanism by determining the structure of reaction intermediate-like states. These can go unnoticed when follow-up studies with other techniques or on wild-type proteins are not carried out (Moffat, 2001).

The scientific question
Feasibility
Prior experimental knowledge
Microcrystal properties: size and homogeneity
Obtaining microcrystals
Initial crystal characterization
Sample delivery
Liquid and viscous jets
Fixed targets
Reaction initiation
Photoactivation
Diffusion or rapid mixing
Crystals versus solution
Shoot it and see?
Data-collection modes
Data-quality assessment
How many data are enough?
Preferred orientation
Isomorphism
Resolution
Scaling statistics
Electron density
Minimum exposure time
Dose limits for room-temperature SSX
Monitoring radiation damage
Pan-data-set analysis
Assessing low-populated states
Singular value decomposition
Clustering
Modelling heterogeneity
10.1. Neutron crystallography
10.2. NMR spectroscopy
10.3. Molecular simulations
10.4. Electronic and vibrational spectroscopy
11. Summary and conclusions
Findings
Funding information

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