Tiancen, One thing that you did not mention. Have you tried examining the crystals at room temperature. Sometimes the cryo-cooling process, or the cyro-buffer, can severely damage a crystal's long-range order. A set of data, or just a few frames, collected at room temperature can determine if the poor diffraction is an intrinsic property of your crystals or due to the cryo-cooling process.
Also have you tried a grid screen around your original conditions? If that fails try a new screen with seeding. You may get good crystals in other conditions nucleating around your seeds. Good luck, Mark On Wed, 2007-01-24 at 17:54 +0800, Tiancen Hu wrote: > Dear all, > > Sorry for the non-CCP4 question. I think this is an old story but our > knowledge to deal with it is very limited. So any suggestions will be greatly > appreciated. > > We have crystallized a 21KD protein with 2 disulfide bonds grown for one > month in 0.1M tri-sodium citrate pH 5.6, 0.5M (NH4)2SO4 and 1M Li2SO4. The > crystals look big (~0.4mm x 0.4mm x 0.3mm) and pretty (sharp edge, clean > surface) but diffracted to only 4A in-house. The spots are quite strong and > isotropic at low resolution but decay sharply beyond 5-6A. The crystal > belongs to P4 pointgroup (P422 is also possible) with cell parameters of > 127.6, 127.6, 162.5, 90, 90, 90. The solutions we can think of to elevate its > diffraction ability are as follows: > > 1) Try synchrotron radiation > 2) Try a lot of similar crystals and hope one of them diffracts better > than others > 3) Let the crystals grow for a longer time and hope it could pack more > “orderly” > 4) Additive screen based on the original condition > 5) Check the original plates for other crystallizing conditions > (unfortunately until now this is the only one out of ~300) > 6) Screen with other forms of the protein, i.e., N/C-terminus truncated > ones, complexed with its ligands etc. > > I believe many protein crystallographers have encountered similar problems, > are there any successful stories from these fancy poor crystals? Any > suggestions or references will be highly appreciated. > > Thanks in advance! > > Tiancen Hu > Shanghai Institute of Materia Medica > Rm. 2107, #555, ZuChongzhi Rd. > Shanghai 201203 > P.R. China > Tel: +86-21-50806600 ext 2107 > Email: [EMAIL PROTECTED] 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
