1The Burnham Institute, La Jolla, CA 92037
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.