W0034

SAS Phasing Using In-House Chromium X-Rays: A Test Bed for Synchrotron Soft X-Ray Applications. John P. Rose^1,2, Zhi-Jie Liu¹, M. Gary Newton¹, John Chrzas², Gerold Rosenbaum², Joe Ferrara³, and B.C. Wang^1,2, ¹Southeast Collaboratory for Structural Genomics, Dept. of Biochemistry and Molecular Biology, Univ. of Georgia, Athens, GA 30602, ²Southeast Regional Collaborative Access Team, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439 and ³Rigaku/MSC, The Woodlands, TX 77381.

Using high intensity chromium radiation (λ = 2.29Å), a test bed for optimizing data collection using synchrotron soft X-rays has been developed aiming to advance Direct Crystallography at SER-CAT as well as at in-house facilities.

Direct Crystallography, structure determination from un-derivatized native protein crystals, relies on the accurate detection of single-wavelength anomalous scattering (SAS) signal from sulfur and/or metals present in the native protein crystals. Since the anomalous scattering signal strength for an atom is dependent on the energy of the X-rays used in the analysis and generally increases with wavelength, soft X-rays (λ ~2Å) should offer a means of increasing the sulfur anomalous scattering signal strength in the data provided that absorption, which also increases with increasing wavelength, can be addressed.

An obvious source of soft X-rays is synchrotron radiation since the wavelength of the X-rays produced is in the range of 0.6 to 2.3 Å depending on beamline configuration. However, most modern beamlines are optimized for data collection near the selenium absorption edge at ~0.97Å dictated by the requirements of the seleno-met MAD experiment and little attention has been paid at optimizing performance in the 1.5 to 2Å wavelength range required for successful sulfur SAS data collection. The soft X-ray test bed we have developed should provide a benchmark and address this problem. Details of the test bed, initial analysis and results will be presented.

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