30th Annual SSRL Users' Meeting — October 9-10, 2003

Low-resolution Phasing by Se-MAD in the Presence of Radiation Damage

C. Bakolitsa,1 K. von Delft,2 A. Gonzalez,3 and R. C. Liddington2

1The Burnham Institute, La Jolla, CA 92037
2The Scripps Research Institute, La Jolla, CA 92037
3Stanford Synchrotron Radiation Laboratory, SLAC, Stanford University, Stanford, CA 94305

With increasingly powerful synchrotron sources, radiation damage is emerging as a limiting factor in determining the success or failure of a Se-MAD experiment. Here, we present the phasing by two-wavelength Se-MAD of weakly diffracting protein crystals affected by significant radiation damage as indicated by a 0.5-0.7% increase in cell dimensions between initial and final frames collected. Data were collected at SSRL 9-1 and made use of some of SSRL's unique features. Internal non-isomorphism rendered global scaling of data invalid, and both Patterson and dual-space direct methods failed to located the anomalous scatterers; these were eventually located by combining local scaling and direct methods.