Macromolecular X-ray Crystallography Facility

Knowledge of molecular structure is essential for our understanding of biological systems.
X-ray crystallography is most widely used to determine the three dimensional structure of proteins, nucleic acids, and large nucleoprotein complexes. It exploits the propensity of X-rays to be scattered by the electron clouds around atoms. The 'electron density' can be reconstructed from diffraction patterns obtained from single crystals of the target molecule (shown below). An atomic model is then built into the electron density, which in turn is refined against the data, eventually resulting in an accurate molecular structure in which the coordinates of every atom with respect to every other atom is known precisely.

The Department of Biochemistry and Molecular Biology at Colorado State University has a state-of-the-art macromolecular X-ray crystallography facility. Crystal growth is performed in a climate controlled crystallization room equipped with two bright field/dark field stereomicroscopes, vibration-isolated shelves for long term crystal tray storage, and two 4-60°C high-precision temperature adjustable incubators for crystal growth. We also have the requisite instruments for freezing, mounting, and storing crystals.

The X-ray generator has a Rigaku RU-H3R rotating anode (target material - Cu), which is capable of up to 18 kW (60 kV, 300 mA) power output. Other notable features are high flux densities (kW/mm2) available over a variety of focal spot sizes, and a two-port system. Both ports are equipped with Imaging plate detectors (R-Axis IV and R-Axis IV++), which have very low background noise and a large aperture (300mm X 300mm) enabling concurrent collection of strong and weak reflections. Both the detectors are equipped with an Osmic confocal multi-layer optics system, which affords us a combination of X-ray beam traits such as, high flux, ideal beam cross-section, and monochromaticity, optimum for our needs. The X-stream 2000 low temperature system generates its own nitrogen and produces a constant cold nitrogen stream for long periods of time allowing data collection at liquid nitrogen temperatures (-180°C) thus minimizing radiation damage to crystals. Instrumentation has recently been expanded by a grant from the W. M. Keck foundation, effectively doubling its capacity. The system yields data of exceptional quality and numerous crystal structures have been determined using this system.

The two ports of the X-ray generator are controlled by separate computers which have the latest versions of Crystal clear and d*TREK allowing simultaneous data collection and processing. These computers have ample data storage capabilities and are also connected to a cluster of linux workstations. These computers are equipped with all the software required for data reduction (HKL2000 and d*TREK), phase determination (CNS, CCP4 program suite, SOLVE / RESOLVE, BnP), and model building (O, and Pymol).

The facilities are being used by the members of the Peersen and Luger lab. Additionally, the Stargell, Hansen, Curthoys, and Nyborg labs are actively involved in structural projects, as are two groups in the Chemistry Department.