The National Institutes of Health (NIH), through its National Center for Research Resources (NCRR), funds MacCHESS for two purposes: core research and support of CHESS users, who perform macromolecular diffraction experiments. MacCHESS staff conduct research in the areas of cell signaling, micro diffraction, membrane proteins, optimized data collection at synchrotron sources, crystallographic phasing, large unit cell crystallography, x-ray optics for crystallography and other areas relevant to macromolecular crystallography. On the user support front, the facility makes available specialized equipment and expertise, in addition to those provided by CHESS to all users. MacCHESS staff provide training and advice in the use of all these amenities. Guidance in determining MacCHESS's major emphases is provided by the MacCHESS Advisory Committee.
Current station CCD configuration
CHESS has actively participated in the development of CCD-based detectors for crystallography, in collaboration with Area Detector Systems Corporation (ADSC); this activity is expected to continue in the future. All MacCHESS stations are equipped with ADSC CCD detectors: Stations A1 and F2 utilize Quantum 210 detectors, 4-chip devices with 4k x 4k 50-micron pixels and a 1-second readout time. Station F1 utilizes a Quantum 270 detector, a similar but slightly larger device with an improved sensitivity for weak data. Station F3 has a Quantum 4 detector, which has 2304 x 2304 80-micron pixels and a somewhat slower readout time but produces excellent data.
Crystal Centering
A "click to center" Java-based graphical user interface employing a high quality digital video camera is available for rapid centering of crystals. Fully automatic centering is now also possible, using the GUI's "Auto Center" button and the XREC software package.
Automation
Automounters are intended to help maximize throughput at synchrotron beam lines where heavy shielding and safety interlocks slow manual access to the experiment. A sizable number of crystals can be stored in the hutch, accessed randomly, mounted and dismounted; all without entering the hutch. A crystal automounter using the ALS design is available at the F1 station.
High Pressure cooling
A facility for cryocooling crystals under pressure is now available at MacCHESS. This technique, developed in the Gruner lab, was reported in (Kim et al., Acta Cryst. D61, 881 (2005)). It involves mounting a crystal on a special pin, pressurizing it, cooling to liquid nitrogen temperature, and then releasing the pressure while keeping the crystal cold. The method can allow successful cryocooling using little or no penetrating cryoprotectant, and can produce cryocooled crystals of better quality than the usual cryocooling method.
Cryo-crystallography
Acquisition of macromolecular crystallography data at low temperatures, using some variation on the crystal mounting loops first developed at Cornell, enables the collection of complete data sets before crystals decay in the high flux synchrotron X-ray beams. Oxford Cryosystems cooling devices with auto-fill capability are available for routine data collection at 100 K at all MacCHESS stations. The temperature is usually set to 100 K, but can be varied from 80 K to 400 K.
Computational Facilities
A number of Linux computers are installed at each MacCHESS beamline and in the CHESS computer room for data collection and processing. Two terabytes of RAID storage are available at each station for user data storage, and gigabit network connections throughout CHESS allow rapid transfer of data during collection and processing operations.
Crystallography software
Popular data reduction packages are available, including HKL2000, DPS/Mosflm/Scala, and XDS. Various general crystallographic software packages are also available, including the full CCP4 Suite, SOLVE/RESOLVE, Arp/wArp, BnP, CNS, Phenix, Coot, PyMol, and O. A variety of methods for data backup and transfer are supported, including portable disks, wired and wireless connections for laptop computers, and network transfer to remote computers via sftp. MacCHESS maintains a Linux Beowulf cluster which can be made available for large computational tasks.
