Priyank, When yo add NaI or KI, is it in addition to the 0.75M NaCl or in place of it? Try replacing the 0.75M NaCl with your halide salt, then your buffers should be isoionic-strength. Also have you tried a CsCl soak? Remember that with all heavy atoms, and halide soaks in particular, you need to collect highly redundant data to get at the signal. If you have access to a synchrotron, then you can use NaBr, for MAD and/or use longer wavelength radiation to increase the anomalous signal from the I or Cs atoms.
Best of luck, Mark On Thu, 2007-06-28 at 18:28 +0100, Priyank Maindola wrote: > Hello all, > I am struggling with getting the phases out for my protein. Heavyatom > database shows that only mercury and samarium have the binding motifs in it. > > Sodium iodide soak is killing the crystal even as less as 0.2 Molar > concentration for 30sec. > With Potassium iodide crystal is okay upto 0.75M for 1 & a half min but the > incorporation is not at relevent sites.(Iodide signal is not distinct and > is weak) > Hg & Au salts precipitate it. > With Pt signal is weak. > Somewhere I read that high salt causes problems for heavy atom to bind to > protein.My protein needs high salt for stability (750mM NaCl) > > Please help with some suggestion!! Sincerely yours, Mark A. White, Ph.D. Assistant Professor, Dept. Biochemistry and Molecular Biology, Manager, Sealy Center for Structural Biology and Molecular Biophysics X-ray Crystallography Laboratory, Basic Science Building, Room 6.660 C University of Texas Medical Branch Galveston, TX 77555-0647 Tel. (409) 747-4747 Fax. (409) 747-4745 mailto://[EMAIL PROTECTED] http://xray.utmb.edu http://xray.utmb.edu/~white
