Automated harvesting and processing of protein crystals through laser photoablation.

Currently, macromolecular crystallography projects often require the use of highly automated facilities for crystallization and X-ray data collection. However, crystal harvesting and processing largely depend on manual operations. Here, a series of new methods are presented based on the use of a low X-ray-background film as a crystallization support and a photoablation laser that enable the automation of major operations required for the preparation of crystals for X-ray diffraction experiments. In this approach, the controlled removal of the mother liquor before crystal mounting simplifies the cryocooling process, in many cases eliminating the use of cryoprotectant agents, while crystal-soaking experiments are performed through diffusion, precluding the need for repeated sample-recovery and transfer operations. Moreover, the high-precision laser enables new mounting strategies that are not accessible through other methods. This approach bridges an important gap in automation and can contribute to expanding the capabilities of modern macromolecular crystallography facilities.

CrystalDirect: a new method for automated crystal harvesting based on laser-induced photoablation of thin films.

The use of automated systems for crystallization and X-ray data collection is now widespread. However, these two steps are separated by the need to transfer crystals from crystallization supports to X-ray data-collection supports, which is a difficult manual operation. Here, a new approach is proposed called CrystalDirect (CD) which enables full automation of the crystal-harvesting process. In this approach, crystals are grown on ultrathin films in a newly designed vapour-diffusion crystallization plate and are recovered by excision of the film through laser-induced photoablation. The film pieces containing crystals are then directly attached to a pin for X-ray data collection. This new method eliminates the delicate step of `crystal fishing', thereby enabling full automation of the crystal-mounting process. Additional advantages of this approach include the absence of mechanical stress and that it facilitates handling of microcrystals. The CD crystallization plates are also suitable for in situ crystal screening with minimal X-ray background. This method could enable the operational integration of highly automated crystallization and data-collection facilities, minimizing the delay between crystal identification and diffraction measurements. It can also contribute significantly to the advancement of challenging projects that require the systematic testing of large numbers of crystals.

A thermal stability assay can help to estimate the crystallization likelihood of biological samples.

The identification of crystallization conditions for biological molecules largely relies on a trial-and-error process in which a number of parameters are explored in large screening experiments. Currently, construct design and sample formulation are recognized as critical variables in this process and often a number of protein variants are assayed for crystallization either sequentially or in parallel, which adds complexity to the screening process. Significant effort is dedicated to sample characterization and quality-control experiments in order to identify at an early stage and prioritize those samples which would be more likely to crystallize. However, large-scale studies relating crystallization success to sample properties are generally lacking. In this study, the thermal stability of 657 samples was estimated using a simplified Thermofluor assay. These samples were also subjected to automated vapour-diffusion crystallization screening under a constant protocol. Analysis of the data shows that samples with an apparent melting temperature (T(m)) of 318 K or higher crystallized in 49% of cases, while the crystallization success rate decreased rapidly for samples with lower T(m). Only 23% of samples with a T(m) below 316 K produced crystals. Based on this analysis, a simple method for estimation of the crystallization likelihood of biological samples is proposed. This method is easy, rapid and consumes very small amounts of sample. The results of this assay can be used to determine optimal incubation temperatures for crystallization experiments or to prioritize certain constructs. More generally, this work provides an objective test that can contribute to making decisions in both focused and structural genomics crystallography projects.