|The IUCr is an International Scientific Union. Its objectives are to promote international cooperation in crystallography and to contribute to all aspects of crystallography, to promote international publication of crystallographic research, to facilitate standardization of methods, units, nomenclatures and symbols, and to form a focus for the relations of crystallography to other sciences.|
A novel nucleating agent that builds on the concept of molecularly imprinted polymers (MIPs) could allow crystallographers access to proteins and other biological macromolecules that are usually reluctant to form crystals. The semi-liquid non-protein agent is reported by UK scientists [Khurshid et al. (2015). Acta Cryst. D71, 534-540; doi: 10.1107/S1399004714027643].
Sahir Khurshid, Lata Govada and Naomi Chayen of Computational and Systems Medicine at Imperial College London, working with chemists Hazim EL-Sharif and Subrayal Reddy of the University of Surrey, Guildford, explain how they have modified MIPs to give the agents a texture suitable for high-throughput trials. Their work shows improvement in crystal quality for those macromolecules that were known to be crystallizable but also boosts the probability of success when they screen for suitable crystallization conditions for more intractable proteins. The team describes the application of these materials as "simple and time-efficient" as well as offering structural biologists a new and potent tool for crystallization trials.
In some sense protein crystallography has stagnated for at least a decade in terms of the success rate in obtaining diffraction-quality, purified crystals. Just one in five protein targets have succumbed during this time. As such, crystallographers have been hunting for agents that could be used to seed crystal growth and make available some of the most important membrane proteins and other biological macromolecules of interest to biomedical scientists and drug developers. Various novel seeding protocols and some nucleating agents have proven useful. However, to be more widely adopted and adapted, Khurshid and colleagues suggest that novel agents must be amenable to high-throughput crystallography applications whilst preferably being non-protein.
In 2011, the team reported that MIPs, which they dubbed "smart materials”, could be used to nucleate crystallization of proteins. The MIPs based on polyacrylamide are synthesized in the presence of a template molecule in solution and a cross-linker reagent. Removal of the template - the protein of interest - after completion of the cross-linking step leaves behind a polymer shell with "ghost sites" containing a fingerprint of the protein. The protein can then be reintroduced under crystallization conditions and so the polymer acts as a support around which the protein might crystallize. At the time, they demonstrated proof of principle with nine proteins. Originally, the team thought that they would need a new MIP for each protein they wished to crystallize but this turned out not to be the case. A single MIP template on one protein could act as a nucleating agent for other proteins of similar molecular weight.
The original MIP agents are gel-like materials, which makes them difficult to manipulate in a high-throughput system, because being viscous they cause blockages in robotic dispensing tips and other figurative bottlenecks in the equipment. An alternative approach might have been to suspend them in a solvent, but this brings its own problems. Instead, the team’s current work has now developed a less viscous - close to that of low molecular weight polyethylene glycol (PEG) - generic MIP that can trap and nucleate different proteins with similar hydrodynamic radii.
The team has now tested their modified MIP agent with six proteins, among them thaumatin (from Thaumatococcus daniellii), bovine pancreatic trypsin, lysozyme (from hen-egg white) and bovine haemoglobin. They then used target proteins, e.g. human macrophage migration inhibitory factor and since publication, a complex of an antibody with a fragment of the CCR5 receptor for the automated optimization trials with the templated MIPs. The agents can be stored at 4 °C for several weeks and only require vortexing if unused to make them "active" again.
"Having patented the design and application of MIPs for crystallization, and validated the modified MIPs for high-throughput trials, the way is now paved for commercialization," the team says.
Radiation damage induced by X-ray beams during macromolecular diffraction experiments remains an issue of concern in structural biology. While advances in our understanding of this phenomenon, driven in part by a series of workshops in this area, undoubtedly have been and are still being made, there are still questions to be answered.
Interest in radiation damage to macromolecules during structural experiments has not abated over the last few years, since there remains a need to understand both the parameters that affect radiation damage progression (the ‘kill’) and also the artifacts produced by it. Although there is now a growing body of literature pertaining to this topic (see for example the special issues of the Journal of Synchrotron Radiation arising from papers presented at the 2nd to 7th International Workshops on Radiation Damage to Biological Crystalline Samples, published in 2002, 2005, 2007, 2009, 2011 and 2013, respectively), clear foolproof methods for experimenters to routinely minimize damage have yet to emerge. Additionally, radiation damage is also a concern and limiting problem in other methods used in structural biology such as electron microscopy, SAXS and scanning X-ray diffraction. However, the recently available free electron lasers (FELs) have presented the possibility and promise that samples will give ‘diffraction before destruction’: is this indeed the ‘cure’ for the challenges of radiation damage?
For the majority of macromolecular crystallographers, using a FEL is not yet a realistic expectation. For them, radiation damage to their samples is likely to become an increasingly observed phenomenon, since much smaller X-ray beams with very high flux densities are becoming available due to upgrades in both electron storage rings and the synchrotrons that feed them. These fourth-generation synchrotrons are engendering even more interest in research into radiation damage and its deleterious effects.
It is clear from a special issue devoted to radiation damage [Garman, E. F. and Weik, M. (2015). J. Synchrotron Rad. 22] that there remains much scope for further studies to inform both experimental practice and the interpretation of the resulting structures so that radiation damage can become a widely recognised and understood facet of structural biology. These experiments on macromolecular crystals will certainly involve more ‘kill’ and, it is to be hoped, some ‘cure’ too.
Like many modern areas of science, structural biology faces enormous challenges created by the vast amount of data generated every day by research groups. As such structural and functional studies require the development of sophisticated "Big Data" technologies and software to increase the knowledge derived and ensure reproducibility of the data. A group of scientists [Berman et al. (2015). IUCrJ. 2, 45-58; doi:10.1107/S2052252514023306] present summaries of the Structural Biology Knowledge Base, the VIPERdb Virus Structure Database, evaluation of homology modelling by the Protein Model Portal, the ProSMART tool for conformation-independent structure comparison, the LabDB "super" laboratory information management system and the Cambridge Structural Database. These techniques and technologies represent important tools for the transformation of crystallographic data into knowledge and information, in an effort to address the problem of non-reproducibility of experimental results.
Two special issues were published in 2014: the first of these, on Crystal Engineering and helmed by Guest Editor Andrew D. Bond appeared in the February issue; the second in August was on Non-ambient Crystallography, with Guest Editors David G. Billing and Andrzej Katrusiak. The special issues helped promote the message of the widening scope of the journal. We had a 64% increase in the number of pages published in the journal, from 633 in 2013 to 1036 in 2014. Further special issues are in progress for 2015-2016, including those on Energy Materials (Guest Editors Simon Parsons, Richard Walton and Karena Chapman), Crystal Structure Prediction (Guest Editors Graeme Day and Carl Henrik Görbitz), and others are planned.
In 2014 the journal published its first Research Perspective article Aperiodic crystals and superspace concepts by Ewald Prize winners Ted Janssen and Aloysio Janner [Janssen, T. & Janner, A. (2014). Acta Cryst. B70, 617-651; doi:10.1107/S2052520615001663]. A research perspective is an article where the main or sole author is an established leader in a particular field and such articles are expected to review the developments of that field, with a strong focus on the author's own contributions to it. The journal will normally publish one article in this category per year and plans for 2015 are currently under way. Leading scientists are welcome to write to us with suggestions and a 500 word outline.
The journal published two feature articles in 2014, Crystalline metal-organic frameworks (MOFs): synthesis and structure and function [Dey et al. (2014). Acta Cryst. B70, 3-10; doi:10.1107/S2052520613029557] and Crystallographic studies of gas sorption in metal-organic frameworks [Carrington et al. (2014). Acta Cryst. B70, 404-422; doi: 10.1107/S2052520614009834]. Future feature articles will include MOFs under high pressure by Stephen Moggach, Prospects for crystal engineering by Christer Aakeröy and contributions by several high-profile speakers at the Montreal IUCr Congress.
Commentaries on some outstanding articles are now appearing regularly in the journal, and we would like to thank the authors of these for their rapid and valuable contributions. Other articles have been highlighted by means of regular news features on the IUCr homepage. The Acta B homepage will be redesigned for 2015, to allow more extensive coverage of recent news items and to highlight outstanding articles and the most cited papers from the journal.
Acta B has an established reputation for publishing work in fields such as aperiodic structures and high-pressure crystallography, and we are working to expand our coverage, including in other areas of materials science and crystal engineering. Acta B has much to offer authors, including speed of publication and high but practical technical standards.
We note that the number of papers where the authors have opted for open access is on the rise: such papers are amongst the most downloaded for the journal.
Finally, the journal will be represented at a number of meetings in 2015, including at the 12th International Conference on Materials Chemistry (MC12, York, UK), the Annual Meeting of the American Crystallographic Association (Philadelphia), and at the 29th European Crystallographic Meeting (ECM29, Rovinj, Croatia). You can see a full list of meetings where IUCr Journals will be displayed by following this link.
This is an excerpt taken from the full editorial which can be found at:
Blake, A. & de Boissieu, M. Acta Cryst. (2015). B71, 1-2; doi:10.1107/S2052520615001663
The following short quiz will test your knowledge and understanding of the Bravais lattice.
(1) What are the Bravais-lattice symbols of the following space groups: No. 2, No. 40, No. 150 and No. 161?
(2) What is the essential geometric difference between the Bravais-lattice types mP and mS? Note: The correct answer contains neither the words 'affine equivalent' nor the words 'unit cell'. Try also the Bravais-lattice types oP, oS, oF and oI.
The 14 Bravais-lattice types are at the very heart of crystallography. It is somewhat remarkable that, in the second decade of the 21st Century, we may still learn new things about them. In Grimmer's paper [Grimmer, H. (2015). Acta Cryst. A71, doi:10.1107/S2053273314027351] he does just this and provides important new insights. Grimmer presents an entirely original way of determining the hierarchical arrangement of Bravais-lattice types. The result is summarised in an easily understood figure. In the figure, the Bravais-lattice type at the upper end of a line is a special case of the type at its lower end. Grimmer's approach to determining the hierarchy is to examine the group-subgroup relations amongst the space groups of the Bravais-lattice types. The latter are those (14) symmorphic space groups with the point group of a holohedry.
[Flack, H.D. (2015). Acta Cryst. A71, doi:10.1107/S2053273315002557]
Successful protein crystallization screening experiments are dependent upon the experimenter being able to identify positive outcomes. The introduction of fluorescence techniques has brought a powerful and versatile tool to the aid of the crystal grower. Trace fluorescent labeling, in which a fluorescent probe is covalently bound to a subpopulation of the protein, enables the use of visible fluorescence. Alternatively one can avoid covalent modification and use UV fluorescence, exploiting the intrinsic fluorescent amino acids present in most proteins. By the use of these techniques, crystals that had previously been obscured in the crystallization drop can readily be identified and distinguished from amorphous precipitate or salt crystals.
Overall, fluorescence, whether intrinsic or by using trace fluorescent labeling (TFL), can be a powerful aid in macromolecule crystallization. Here Meyer et al. [(2015). Acta Cryst. F71, 121-131; doi:10.1107/S2053230X15000114] have only discussed its use in screening for crystals, although other applications in the field of macromolecule crystallization and crystal growth are possible. Simple instrumentation incorporating the requisite basic functionality for the three main approaches discussed in the paper can be realized in even a small structural biology laboratory. The benefits obtained are powerful aids in interpreting the screening results as well as obtaining potential insights leading to additional, previously unrealized, lead conditions.