Non-Contact Universal Sample Presentation for Room Temperature Macromolecular Crystallography Using Acoustic Levitation

R H Morris,P T Docker,J H Beale,D Axford,M I Newton,E R Dye

doi:10.1038/s41598-019-48612-4

Abstract

Macromolecular Crystallography is a powerful and valuable technique to assess protein structures. Samples are commonly cryogenically cooled to minimise radiation damage effects from the X-ray beam, but low temperatures hinder normal protein functions and this procedure can introduce structural artefacts. Previous experiments utilising acoustic levitation for beamline science have focused on Langevin horns which deliver significant power to the confined droplet and are complex to set up accurately. In this work, the low power, portable TinyLev acoustic levitation system is used in combination with an approach to dispense and contain droplets, free of physical sample support to aid protein crystallography experiments. This method facilitates efficient X-ray data acquisition in ambient conditions compatible with dynamic studies. Levitated samples remain free of interference from fixed sample mounts, receive negligible heating, do not suffer significant evaporation and since the system occupies a small volume, can be readily installed at other light sources.

Highlights

In recent years synchrotron MX beamlines have adopted similar methods to those created for XFELs as some are directly transferable, such as the fixed-targets[9] and LCP extruders[10]
Protein crystals are typically grown in solvents with high surface tensions and the crystal solution often remains attached to the pipette tip during loading into the levitation field
We have found that the incorporation of silicon oil coat around the protein crystal solution dramatically increases the ease of delivering the levitating drop incorporating the sample crystal

Summary

Introduction

In recent years synchrotron MX beamlines have adopted similar methods to those created for XFELs as some are directly transferable, such as the fixed-targets[9] and LCP extruders[10]. A technique which does not introduce any crystalline non-sample material into the beamline is acoustic levitation, where the sample is presented without contact from external supports as has been previously demonstrated for MX at the Swiss Light Source[16] This builds on other X-Ray scattering experiments with levitated samples such as at the MAX II, Sweden[17] and BESSY, Germany[18,19]. We have found that the incorporation of silicon oil coat around the protein crystal solution dramatically increases the ease of delivering the levitating drop incorporating the sample crystal This method has solved a significant barrier to entry for acoustically levitating MX samples and will open up new avenues of automated sample delivery. We have determined the optimum system voltage to trap relevant sample volumes to maximise the applicability of the encapsulated droplet approach

Methods

Results

Conclusion