Protein Crystallography Newsletter
Volume 1, No. 3, April 2009

In this issue:

• Crystallography in the news
• CCD detectors for the home lab
• Upcoming crystallography meetings
• X-ray safety - what everyone should know
• Useful links for crystallography
• Selected recent crystallographic papers
• FAQ: finding the direct beam center
• Survey question of the month

Continuing Education Webinar X-ray Radiation Safety What Everyone Should Know Presenter: Dr. Kris Tesh May 27 at 12:00 PM EDT (16:00 GMT) Click here to register

Saturn A200 (top) and Saturn 944+ (bottom) 18-bit CCD detector systems deliver speed with high dynamic range.

Click here for a comprehensive list of upcoming
crystallography meetings and conferences.

Crystallography in the news

April 17, 2009. Glaxo and Pfizer form a London-based joint venture, with both drugmakers pooling resources in a bid to boost financial returns from tackling HIV/AIDS.

April 15, 2009. Review of detection method for conformational change in proteins. Second-Harmonic Generation (SHG) provides a molecular-level, functional readout in real time.

April 14, 2009. Scripps group announces the discovery of mimicry at the molecular level that protects genome integrity. The research draws new parallels between the Rad60 DNA repair factor and SUMO, a small ubiquitin-like modifier, which are both essential for maintaining genome stability during replication.

CCD detectors for the home lab

Both Imaging Plate (IP) and CCD based detectors are commonly used in home X-ray diffraction labs. Depending on the application and circumstance, there are unique and distinct advantages associated with both technologies. The primary benefits of CCD detectors are fast read out and cycle times. This is an important consideration for labs that need to screen numerous samples in a short time.

Faster read times also make CCD detectors ideal for experiments with short exposure times. Exposure times may become short enough that the detector read out time may be the rate limiting step in collecting diffraction data in a home X-ray lab. Both the Saturn 944+ and the Saturn A200 detectors provide read times of under one second and use parallel image processing (PIP) to minimize shutter closed times to less than 2 seconds between images.

The Saturn 944+ uses a single CCD chip providing a 94x94mm active area and is coupled with a flexible 4-axis goniometer to allow complete, high resolution data collection. The larger Saturn A200 employs an array of four CCD chips providing a 203x203mm active area that allows for high resolution data to be collected with no 2Θ swing. For medium to high throughput labs, a Saturn CCD detector will enable both rapid crystal screening and high quality data collection. To provide a perspective on CCD detectors, the unique benefits of Imaging Plate (IP) detectors will be discussed in a future eNewsletter.

Request a copy of the Saturn 944+ or Saturn A200 brochure.

X-ray safety - what everyone should know

The new Rigaku Life Sciences Webinar Series continues on May 27th with a discussion on X-ray radiation safety in the home lab. Hosted by Kris Tesh, Ph.D., this complementary continuing education seminar is recommended viewing for students or as a refresher for routine users and their staff. Click here to register.

Useful links for crystallography

P212121 - Ted Erickson's informative and entertaining blog about protein crystallography.

Reciprocal Space, a protein crystallography blog by Stephen Curry.

Selected recent crystallographic papers

Crystal structure of human spliceosomal U1 snRNP at 5.5 Å resolution. D.A. Pomeranz Krummel, C. Oubridge, A.K.W. Leung, J. Li and K. Nagai. Nature 458, 475-480 (2009).

X-ray structure of the ternary MTX.NADPH complex of the anthrax dihydrofolate reductase: a pharmacophore for dual-site inhibitor design. B.C. Bennett, Q. Wan, M.F. Ahmad, P. Langan and C.G. Dealwis. Journal of Structural Biology 166, 2, 162-71 (2009).

Structure of P-glycoprotein reveals a molecular basis for poly-specific drug binding. S.G. Aller, J. Yu, A. Ward, Y. Weng, S. Chittaboina, R. Zhuo, P.M. Harrell, Y.T. Trinh, Q. Zhang, I.L. Urbatsch and G. Chang. Science 323, 5922, 1718-1722 (2009).

FAQ: finding the direct beam center

Accurately knowing the direct beam position (X,Y coordinates of the direct beam) is important for proper indexing and processing of X-ray diffraction data. Although a small error in the direct beam position usually does not create any problems, the error needs to be less than half the distance between the diffraction spots from the longest unit cell edge in the diffraction pattern. If you are having trouble indexing data then it may indicate that your direct beam position is not accurate. The "Beam center" utility from d*TREK^® can be used in either StructureStudio™ or the stand alone version of d*TREK to quickly and easily find the correct beam center position.

Ice rings, and powder or solvent diffraction that show a well defined diffraction ring, can be used to find the correct beam center. In StructureStudio, the utility called "Beam center" can be found in the right click menu of an "Image Viewer" view (or alternatively by pressing Alt+B). This will generate a blue circle and all you need to do to find the beam center is to align this circle with the ice ring circle, as shown in the images to the left. The beam center is the center of this blue circle. In d*TREK the same thing can be done using the "Beam circle" utility in dtdisplay. This functionality in StructureStudio and d*TREK makes finding the beam center very easy and is useful for data sets that have been collected in the home lab and also at beamlines.