Currently, once a hit has been obtained from the initial crystallization screening step, optimized crystals are grown based on that hit and mounted in cryoloops and cryogenically preserved. The crystals are then screened in the laboratory and shipped to the synchrotron for data collection. Screening takes place remotely using the Stanford Auto Mounting system (SAM) (Cohen at al., 2002). This uses cassettes holding 96 crystals at a time. Mounting the 96 crystals required for each cassette is a manual process and one that significantly slows down the pipeline. To overcome this, we are developing plastic capillary-based crystallization and handling methods.

The use of capillaries enables the same batch method as used for crystallization screening and optimization. At the same time, it allows automated handling of the sample. By designing the capillaries with a pipette tip mount, we also enable automated filling. A new sample capillary compatible with the SAM system is being developed. The sample capillary (shown in Figure 1) resembles a pipette tip, and the first prototypes are being produced from injection-molded polycarbonate. Sample capillaries made from alternative materials will also be fabricated and tested for improved performance including optimization of surface properties for crystal growth. The portion of this specialized pipette tip that will hold samples is a very thin-walled, small diameter capillary. It is transparent so that crystals inside may be visually identified.  When used for x-ray data collection, the capillary will produce only a low x-ray background. Therefore, complete high-quality datasets may be collected from samples within the capillary. 

The capillary, designed to fit within the dimensions available for an SSRL-style cassette, is also short enough to fit inside a uni-puck (Figure 2). The development of the uni-puck was a collaborative project initiated by SSRL staff to develop a universal sample pin storage and shipping container compatible with the majority of automated sample mounting systems used at synchrotron beam lines. This enables us to perform the data collection step at most synchrotrons or laboratories that have an automated sample mounter.

Reference

Cohen, A. E., Ellis, P. J., Miller, M. D., Deacon, A. M., and Phizackerley, R. P. (2002): An automated system to mount cryo-cooled protein crystals on a synchrotron beamline, using compact sample cassettes and a small-scale robot. J. Appl. Cryst. 35, 720-726.