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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 ´orderlyˇ > 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: [log in to unmask] 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:[log in to unmask] http://xray.utmb.edu http://xray.utmb.edu/~white