Automation of High-Throughput Protein Crystal Screening at SSRLAina Cohen SSRL entered a new era of synchrotron radiation experimentation in March
2004 with the start of the first experimental run following the completion
of the SPEAR3 upgrade project. Intense x-rays at the macromolecular
crystallography stations, combined with state-of-the-art equipment,
including high-speed CCD detectors and sophisticated control system software
now enable high-quality diffraction images to be collected in only a few
seconds and entire datasets in a matter of minutes. With significant
reduction in the time required to collect a dataset, the period necessary to
enter the experimental hutch to manually mount and dismount crystal samples
is often a significant percentage of the users' total beam time allocation.
To improve the efficient use of the synchrotron resource, the Structure
Determination Core of the Joint Center for Structural Genomics (JCSG) and
the SSRL Structural Molecular Biology Group have worked together to develop
the Stanford Auto-Mounting (SAM) system. SAM is a completely integrated
hardware and software system for mounting and dismounting pre-frozen protein
crystals and screening samples for x-ray diffraction quality in a fully
automated or semi-automated fashion. SAM is installed on all of the SSRL
macromolecular crystallography beamlines and is seamlessly integrated into
the Blu-Ice/DCS beamline control system. A typical screening sequence takes
3 minutes per crystal (robotic crystal mounting, automatic sample loop
centering in the x-ray beam, video and diffraction image acquisition at 0
and 90o, and dismounting). This enables up to 288 samples to be screened in
less than 15 hours without opening the experimental hutch door. In 2004, the
SAM system was made available to general users during the first SPEAR3 run
on three beamlines. It was used during 60 experimental user runs by 30
different research groups. During the same period, members of the JCSG group
used SAM to screen more than 2000 crystals from 125 target proteins. From
these, 56 datasets were collected from 36 unique proteins, resulting in 30
new structures. So far during the 2005 user run SAM has been used for about
half of the protein crystallography experiments and the option for fully
remote data collection has been made available to general users. For
pre-frozen samples the new technologies being implemented at SSRL will
eliminate the distinction between remote and local access to synchrotron
resources. |