UV LED lighting for automated crystal centring

DeepCentering: fully automated crystal centering using deep learning for macromolecular crystallography

High-throughput protein crystallography using a synchrotron light source is an important method used in drug discovery. Beamline components for automated experiments including automatic sample changers have been utilized to accelerate the measurement of a number of macromolecular crystals. However, unlike cryo-loop centering, crystal centering involving automated crystal detection is a difficult process to automate fully. Here, DeepCentering, a new automated crystal centering system, is presented. DeepCentering works using a convolutional neural network, which is a deep learning operation. This system achieves fully automated accurate crystal centering without using X-ray irradiation of crystals, and can be used for fully automated data collection in high-throughput macromolecular crystallography.

The fine art of integral membrane protein crystallisation

Integral membrane proteins are among the most fascinating and important biomolecules as they play a vital role in many biological functions. Knowledge of their atomic structures is fundamental to the understanding of their biochemical function and key in many drug discovery programs. However, over the years, structure determination of integral membrane proteins has proven to be far from trivial, hence they are underrepresented in the protein data bank. Low expression levels, insolubility and instability are just a few of the many hurdles one faces when studying these proteins. X-ray crystallography has been the most used method to determine atomic structures of membrane proteins. However, the production of high quality membrane protein crystals is always very challenging, often seen more as art than a rational experiment. Here we review valuable approaches, methods and techniques to successful membrane protein crystallisation.

Crystallophore: a versatile lanthanide complex for protein crystallography combining nucleating effects, phasing properties, and luminescence

Macromolecular crystallography suffers from two major issues: getting well-diffracting crystals and solving the phase problem inherent to large macromolecules. Here, we describe the first example of a lanthanide complex family named "crystallophore" (Xo4), which contributes to tackling both bottlenecks. This terbium complex, Tb-Xo4, is an appealing agent for biocrystallography, combining the exceptional phasing power of the Tb(iii) heavy atom with powerful nucleating properties, providing ready-to-use crystals for structure determination. Furthermore, protein/Tb-Xo4 co-crystals can be easily detected and discriminated from other crystalline by-products using luminescence. We demonstrate the potential of this additive for the crystallisation and structure determination of eight proteins, two of whose structures were unknown.

Locating and Visualizing Crystals for X-Ray Diffraction Experiments

Macromolecular crystallography has advanced from using macroscopic crystals, which might be >1 mm on a side, to crystals that are essentially invisible to the naked eye, or even under a standard laboratory microscope. As crystallography requires recognizing crystals when they are produced, and then placing them in an X-ray, electron, or neutron beam, this provides challenges, particularly in the case of advanced X-ray sources, where beams have very small cross sections and crystals may be vanishingly small. Methods for visualizing crystals are reviewed here, and examples of different types of cases are presented, including: standard crystals, crystals grown in mesophase, in situ crystallography, and crystals grown for X-ray Free Electron Laser or Micro Electron Diffraction experiments. As most techniques have limitations, it is desirable to have a range of complementary techniques available to identify and locate crystals. Ideally, a given technique should not cause sample damage, but sometimes it is necessary to use techniques where damage can only be minimized. For extreme circumstances, the act of probing location may be coincident with collecting X-ray diffraction data. Future challenges and directions are also discussed.

Automatic crystal centring procedure at the SSRF macromolecular crystallography beamline

X-ray diffraction is a common technique for determining crystal structures. The average time needed for the solution of a protein structure has been drastically reduced by a number of recent experimental and theoretical developments. Since high-throughput protein crystallography benefits from full automation of all steps that are carried out on a synchrotron beamline, an automatic crystal centring procedure is important for crystallographic beamlines. Fully automatic crystal alignment involves the application of optical methods to identify the crystal and move it onto the rotation axis and into the X-ray beam. Crystal recognition has complex dependencies on the illumination, crystal size and viewing angles due to effects such as local shading, inter-reflections and the presence of antifreezing elements. Here, a rapid procedure for crystal centring with multiple cameras using region segment thresholding is reported. Firstly, a simple illumination-invariant loop recognition and classification model is used by slicing a low-magnification loop image into small region segments, then classifying the loop into different types and aligning it to the beam position using feature vectors of the region segments. Secondly, an edge detection algorithm is used to find the crystal sample in a high-magnification image using region segment thresholding. Results show that this crystal centring method is extremely successful under fluctuating light states as well as for poorly frozen and opaque samples. Moreover, this crystal centring procedure is successfully integrated into the enhanced Blu-Ice data collection system at beamline BL17U1 at the Shanghai Synchrotron Radiation Facility as a routine method for an automatic crystal screening procedure.

Current advances in synchrotron radiation instrumentation for MX experiments

Following pioneering work 40 years ago, synchrotron beamlines dedicated to macromolecular crystallography (MX) have improved in almost every aspect as instrumentation has evolved. Beam sizes and crystal dimensions are now on the single micron scale while data can be collected from proteins with molecular weights over 10 MDa and from crystals with unit cell dimensions over 1000 Å. Furthermore it is possible to collect a complete data set in seconds, and obtain the resulting structure in minutes. The impact of MX synchrotron beamlines and their evolution is reflected in their scientific output, and MX is now the method of choice for a variety of aims from ligand binding to structure determination of membrane proteins, viruses and ribosomes, resulting in a much deeper understanding of the machinery of life. A main driving force of beamline evolution have been advances in almost every aspect of the instrumentation comprising a synchrotron beamline. In this review we aim to provide an overview of the current status of instrumentation at modern MX experiments. The most critical optical components are discussed, as are aspects of endstation design, sample delivery, visualisation and positioning, the sample environment, beam shaping, detectors and data acquisition and processing.

Exploiting Microbeams for Membrane Protein Structure Determination

A reproducible, and sample independent means of predictably obtaining large, well-ordered crystals has proven elusive in macromolecular crystallography. In the structure determination pipeline, crystallisation often proves to be a rate-limiting step, and the process of obtaining even small or badly ordered crystals can prove time-consuming and laborious. This is particularly true in the field of membrane protein crystallography and this is reflected in the limited number of unique membrane protein structures deposited in the protein data bank (less than 650 by June 2016 - http://blanco.biomol.uci.edu/mpstruc ). Over recent years the requirement for, and time and cost associated with obtaining, large crystals has been partially alleviated through the development of beamline instrumentation allowing data collection, and structure solution, from ever-smaller crystals. Advances in several areas have led to a step change in what might be considered achievable during a synchrotron trip over the last decade. This chapter will briefly review the current status of the field, the tools available to ease data collection and processing, and give some examples of exploitation of these for membrane protein microfocus macromolecular crystallography.

Identifying, studying and making good use of macromolecular crystals

As technology advances, the crystal volume that can be used to collect useful X-ray diffraction data decreases. The technologies available to detect and study growing crystals beyond the optical resolution limit and methods to successfully place the crystal into the X-ray beam are discussed.

Structural biology has contributed tremendous knowledge to the understanding of life on the molecular scale. The Protein Data Bank, a depository of this structural knowledge, currently contains over 100 000 protein structures, with the majority stemming from X-ray crystallography. As the name might suggest, crystallography requires crystals. As detectors become more sensitive and X-ray sources more intense, the notion of a crystal is gradually changing from one large enough to embellish expensive jewellery to objects that have external dimensions of the order of the wavelength of visible light. Identifying these crystals is a prerequisite to their study. This paper discusses developments in identifying these crystals during crystallization screening and distinguishing them from other potential outcomes. The practical aspects of ensuring that once a crystal is identified it can then be positioned in the X-ray beam for data collection are also addressed.

Towards protein-crystal centering using second-harmonic generation (SHG) microscopy

The potential of second-harmonic generation (SHG) microscopy for automated crystal centering to guide synchrotron X-ray diffraction of protein crystals was explored. These studies included (i) comparison of microcrystal positions in cryoloops as determined by SHG imaging and by X-ray diffraction rastering and (ii) X-ray structure determinations of selected proteins to investigate the potential for laser-induced damage from SHG imaging. In studies using β2 adrenergic receptor membrane-protein crystals prepared in lipidic mesophase, the crystal locations identified by SHG images obtained in transmission mode were found to correlate well with the crystal locations identified by raster scanning using an X-ray minibeam. SHG imaging was found to provide about 2 µm spatial resolution and shorter image-acquisition times. The general insensitivity of SHG images to optical scatter enabled the reliable identification of microcrystals within opaque cryocooled lipidic mesophases that were not identified by conventional bright-field imaging. The potential impact of extended exposure of protein crystals to five times a typical imaging dose from an ultrafast laser source was also assessed. Measurements of myoglobin and thaumatin crystals resulted in no statistically significant differences between structures obtained from diffraction data acquired from exposed and unexposed regions of single crystals. Practical constraints for integrating SHG imaging into an active beamline for routine automated crystal centering are discussed.

Beamline AR-NW12A: high-throughput beamline for macromolecular crystallography at the Photon Factory

AR-NW12A is an in-vacuum undulator beamline optimized for high-throughput macromolecular crystallography experiments as one of the five macromolecular crystallography (MX) beamlines at the Photon Factory. This report provides details of the beamline design, covering its optical specifications, hardware set-up, control software, and the latest developments for MX experiments. The experimental environment presents state-of-the-art instrumentation for high-throughput projects with a high-precision goniometer with an adaptable goniometer head, and a UV-light sample visualization system. Combined with an efficient automounting robot modified from the SSRL SAM system, a remote control system enables fully automated and remote-access X-ray diffraction experiments.