November 1, 2005

NSLS 2005 Annual Users’ Meeting Workshop

The Impact of Cryogenic Specimen Automounters on the Future of Macromolecular Crystallography

Cryogenic "automounters" are becoming common at synchrotron x-ray sources and in a few commercial laboratories, employed especially in macromolecular crystallography (PX). There are several commercially available models, and several home-built ones, used in a range of synchrotron radiation sources around the world. This workshop gave the PX community an opportunity to hear the major builders of these instruments describe important features of the operation of their instruments, and the ways the scientific community is using them.

Thomas Earnest's group at Lawrence Berkeley National Laboratory's Advanced Light Source (LBL/ALS) designed one of the most imitated automounter systems, based on pneumatic actuators. He summarized their experience at the ALS with the design, now exported to several locations (the NSLS, the Advanced Photon Source (APS), and the Macromolecular Diffraction Facility at the Cornell High-Energy Synchrotron Source (CHESS)). He emphasizes an "open source" view of the design to encourage information sharing and described many small improvements since the original design. They're working on a Cartesian robot to replace the current system, which would not require the crystal-supply Dewar to move, and would have a larger capacity. Dieter Schneider, BNL Biology Department, described his group's refinement of the LBL/ALS system. They devised a three-jaw gripper that is being adopted at several places, developed innovations that minimize frosting of the lid, and are beginning to develop EPICS-based control. Gerd Rosenbaum, of the Southeast Regional Collaborative Access Team at the APS, described his group's adaptation of this design. This instrument is just now coming into operation. Quan Hao, CHESS, gave the same sort of report, one innovation being a miniature liquid nitrogen pump for filling the sample dewar, and described his use of a Java-based camera system for sample viewing.

Aina Cohen represented the Stanford Synchrotron Radiation Laboratory (SSRL) robot effort, one of the earliest in the PX community, whose device depends on an industrial robot for flexibility. They have very much experience and have made many refinements to the original system to provide reliability. The SSRL group has developed a web site for sharing ideas about automounters: http://smb.slac.stanford.edu/robosync/.

Franck Felisaz, of the Joint Structural Biology Group at the European Synchrotron Radiation Facility's (ESRF) European Molecular Biology Laboratory (EMBL), Medical Research Council Grenoble, described a robot named SC3 that was developed at the EMBL. Eight of these have been built for ESRF, commercialized through Maatel and marketed through Accel. An especially attractive feature is the software, which can be used with a pocket PC to read bar code labels on crystal-growth trays in order to transfer that information to the data-collection software. Bernard Lavault, also from EMBL, described image-recognition software ("C3D") for locating and centering crystals on the goniometer. It has an impressive record of finding the real crystal in globs of vitrified liquid. He emphasized the importance of lighting and the ability to vary lighting direction and intensity. Deming Shu, a member of the instrument-development group at the APS, described their design of a custom robotic system based on a commercial six-axis robot. There are many refinements, in particular a force-sensing gripper.

Several commercially available robotic systems were described as well. Ross Doyle of Mar USA described the MAR Cryogenic Sample Changer, which can be provided as part of MAR dtb (desk-top beamline). This system is used at several places in Europe and at the Structural GenomiX beam line at the APS. Anne Mulichak, a member of the Industrial Macromolecular Crystallography Association Collaborative Access Team (IMCA-CAT) at the APS, described their experience using ACTOR, the six-axis robot produced by Molecular Structure Corporation of The Woodlands, Texas. This instrument is an engineered adaptation of the first such robot ever produced (by Abbott Pharmaceuticals for their internal use). After a few years' experience at IMCA-CAT the machine is in fairly routine use now. Ehmke Pohl of the Swiss Light Source reported that they purchased one two-Dewar ACTOR system. They put special effort into accurately intersecting the x-ray beam with the crystal, employing x-ray beam position monitors to provide feedback for 10-micrometer positional stability. They're looking into using ultraviolet sensing together with visible light to locate the sample. Finally, Bob He, from the Bruker-Nonius company of Madison, Wisconsin, described yet another quite successful commercial robot based on a six-axis system. This system has found acceptance in the home-lab small-molecule community, and it works just fine in PX.

An hour and a half were reserved at the end of the workshop for open discussion. The critical item was to discuss seriously (both builders and users) the standardization of the fixtures the experimenters use to handle their specimens: crystal "caps" and pins, and the cassettes used to carry the caps to the automount robot. The discussion yielded important, detailed ideas that have been passed on to the American Crystallographic Association Data, Standards, and Computing Committee.

FOR MORE INFORMATION
Robert Sweet
Biology Department
Brookhaven National Laboratory
Upton, NY Email: sweet@bnl.gov

Ward W. Smith
GM/CA Collaborative Access Team
Advanced Photon Source and Biosciences Division
Argonne National Laboratory
Argonne, IL
Email: wwsmith@anl.gov