A protein crystallography MAD beamline installed
on the 7 T wiggler at the LSU/CAMD synchrotron.

Introduction
The Gulf Coast Protein Crystallography Consortium (GCPCC) formed in response to the needs of local users for greater access to synchrotron radiation sources for the determination of protein crystallographic structures. After several years of discussion, which grew out of a regional, annual protein crystallography meeting, members of the consortium began to evaluate beamline designs for the CAMD synchrotron at LSU. Specifically, the consortium members wanted increased access to a synchrotron beamline with MAD phasing capabilities. MAD phasing has become an important method of solving protein structures and requires a synchrotron source. Many projects, however, were delayed while waiting for available beam time at national facilities. The location of the beamline at CAMD has the advantage of close proximity to the consortium members. This regionality of the facility is important in that it reduces travel expenses and makes it more feasible for groups to bring graduate students along on data collection trips as part of their training. Additionally, the installation of an energy-shifting wiggler makes the CAMD source characteristics well suited for macromolecular crystallography.

The GCPCC beamline is currently operational and is capable of standard macromolecular MAD phasing experiments over an energy range of 7.0-17.5 keV, which includes absorption edges of elements from Fe to Rb and Gd to U. Rather than design a system de novo, the GCPCC has taken the information and experience learned at the national labs over many years to implement an effective protein crystallographic beamline that delivers a useful flux.  

Beamline Design
The primary optical elements of the system are a vertical collimating mirror, a Si (111) channel-cut monochromator, and a focusing mirror (Figure 1). The first mirror serves to collimate the beam vertically, which improves the energy resolution of the monochromator. The Si (111) channel-cut monochromator selects the desired wavelength. The channel-cut design reduces the number of degrees of freedom and simplifies alignment of the beamline. The second mirror is a cylinder that is bent to focus the the beam in both the vertical and horizontal directions (Figure 3). The endstation has a Mar Research 165 mm dia. CCD based X-ray detector with a Mar Research dtb single-axis goniostat, an Oxford Instruments Cryojet cryocooler and a system for measuring the X-ray fluorescence spectrum from the sample crystal. The GCPCC can effectively focus approximately 1.5 mrad of the wiggler fan.

Figure 1. Schematic anamorphic diagram of the GCPCC beamline showing the position of the vertical collimating mirror (M1) the channel-cut monochromator and focusing toroidal mirror (M2) in relation to the source and focus locations.

Figure 2. Schematic of the channel-cut monochromator for the GCPCC beamline. "White" light enters from the left and "monochromatic" light exits to the right. Click on the image for an animated illustration.

The resulting foucus looks as follows.

Figure 3. GCPCC beamline focused spot results from ray-tracing the beamline in SHADOW. A 200 µm yellow square is shown on the close-up view for reference.

Having begun operation in January 2003, the GCPCC beamline serves as a regional research and training facility.  By providing improved access to a MAD capable synchrotron radiation beamline, it can accelerate the solution of new structures.  Located close to the consortium laboratories, the beamline facilitates the participation of new students in the solution of protein and nucleic acid structures.  The GCPCC beamline has allocated 25 % of the beamline time to general users.  We are also implementing a "FedEx data collection" program like the one developed at the NSLS as a method for meeting some of this 25 % commitment. 

The CAMD Facility
The Center for Advanced Microstructures and Devices (CAMD) at Louisiana State University (LSU) operates an electron storage ring for the production of synchrotron radiation.  This second generation source with a Chasman-Green lattice has been operational since 1992.  The ring currently operates at 1.3 GeV with an injection current of 200 mA and 2 fills per day.  The installation of a super-conducting, energy-shifting wiggler enables the production of a significant flux in a range of energies of interest to macromolecular crystallographers.

Figure 4. Synchrotron radiation spectra for a CAMD bend and the CAMD Wiggler at 1.3 GeV.

Figure 5 . Picture of the CAMD synchrotron facility.

Figure 6 . Location of the GCPCC beamline at CAMD.