W0101

Phasing on Solvent Halides. Z. Dauter, K. Rajashankar, M. Dauter, NCI and NSLS, Brookhaven Nat. Lab., Bldg. 725A-X9, Upton, NY 11973.

When protein crystals are soaked in the cryosolution containing sub-molar concentration of a halide salt, the bromide or iodide ions diffuse in and adopt ordered sites around the protein. The sites are shered by halides and waters with various occupancies. The presence of halide ions can be utilized for structure solution. Bromides are suitable for MAD or SAD approach, with its K absorption edge at 0.92 Å wavelength. Iodides show a significant anomalous signal at longer wavelengths, with about 7 anomalous electron units at the copper wavelength, and is good for MIRAS approach. It should be taken into account that the absorption edge of ordered bromide ions, contributing to diffraction data, is shifted by about 3 eV towards lower energy from the signal of totally disordered solvent bromides, observed in the fluorescence spectrum. The cryoderivatization with halides is quick and easy and may be particularly appropriate for high-throughput structure genomics projects.