SAD phasing of a structure based on cocrystallized iodides using an in-house Cu Kα X-ray source: effects of data redundancy and completeness on structure solution

Superoxide dismutase (SOD) from Potentilla atrosanguinea (Wall. ex. Lehm.) was crystallized using 20% PEG 3350 and 0.2 M ammonium iodide and diffraction data were collected to 2.36 Å resolution using an in-house Cu Kα X-­ray source. Analyses show that data with a redundancy of 3.2 were sufficient to determine the structure by the SAD technique using the iodine anomalous signal. This redundancy is lower than that in previous cases in which protein structures were determined using iodines for phasing and in-house copper X-ray sources. Cocrystallization of proteins with halide salts such as ammonium iodide in combination with copper-anode X-ray radiation can therefore serve as a powerful and easy avenue for structure solution.