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.