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Dear Tiancen, Try to purify your protein further by IEX column. Sometimes it improve crystal quality drastically. See: http://dx.doi.org/10.1107/S1744309105023080 Acta Cryst. (2005). F61, 788-790 [ doi:10.1107/S1744309105023080 ] E. Honjo, T. Tamada, Y. Maeda, T. Koshiba, Y. Matsukura, T. Okamoto, M. Ishibashi, M. Tokunaga and R. Kuroki Crystallization of a 2:2 complex of granulocyte-colony stimulating factor (GCSF) with the ligand-binding region of the GCSF receptor Hope it helps. Takaaki Fukami ----- Dr. Takaaki Fukami (mailto:[log in to unmask]) Chemistry Research Dept.2 Gr.4 Roche Group: Chugai Pharmaceutical Co.,Ltd. -----Original Message----- From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of Tiancen Hu Sent: Wednesday, January 24, 2007 6:54 PM To: [log in to unmask] Subject: [ccp4bb] Fancy crystal, poor diffraction 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: [log in to unmask]