W0221

Crystal Structure Determination Using In-House Chromium X-Ray Source. Zhi-Jie Liu¹, John Rose¹, Wolfram Tempel¹, Ashit Shah¹, Doowan Lee¹, Jeff Habel¹, Gary Newton¹, Chwan-Deng Hsiao² and Bi-Cheng Wang¹, ¹Southeast Collaboratory for Structural Genomics, Dept. of Biochemistry and Molecular Biology, Univ. of Georgia, Athens, GA 30602, ²Institute of Molecular Biology, Academia Sinica, Nankang, Taiwan, Taipei, 115, ROC.

Solving protein crystal structures using only the native crystals by a process we termed Direct Crystallography has been our long-term interest. Sulfur, existing in almost every protein, has been used as the phasing probe in our previous studies (1,2). As a test if X-rays with wavelengths that are longer than Cu-radiation would enhance the success rate of sulfur phasing, we have recently installed an Osmic CMF optic to a RU-200 generator system with a Cr anode. From Cu X-rays (λ = 1.54 Å) to Cr X-rays (λ = 2.29Å) the value of Δf” is more than doubled from 0.56 e^- to 1.15 e^-. Following this known fact, a question may be asked: does doubling of the Δf” value alone make a significant difference in sulfur phasing, in view of many other factors which may be unfavorable for data collection at a longer wavelength?

Since the installation of our Cr source, four sets of diffraction data have been collected in the last 30 days. We have now solved all four structures by sulfur phasing with data collected on a R-AXIS IV imaging plate detector. The use of longer wavelength X-rays indeed significantly increases the success rate of sulfur phasing. Details of the experimental aspects and results will be presented.

Wang BC. (1985). Methods Enzymol, 115:90-112.

Liu, Z.-J., Vysotski, E. S., Chen, C. J., Rose, J. P., Lee, J., and Wang, B.C. (2000). Protein Sci. 9, 2085-2093

Work supported in part with funds from the National Institute of Health (GM62407), The Georgia Research Alliance, and The University of Georgia Research Foundation, Rigaku/MSC, IBM.