Dear Sangheon, there is no law that forbids P21 crystals to have a~b~c and beta~90°. It only does not happen very often. So your solution can be correct. You may want to analyze your crystal packing with ccp4 program Zanuda, to see if a higher symmetry space group could be used.
Best regards, Herman Von: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] Im Auftrag von ??? Gesendet: Freitag, 25. Oktober 2013 02:56 An: CCP4BB@JISCMAIL.AC.UK Betreff: [ccp4bb] strange unit cell Hi everyone, Recently I've got a protein crystal and I did indexing and scaling with a cubic space group (unit cell 104.115 104.115 104.115 90.0 90.0 90.0). But a Rmerge value was too high (around 0.5-0.6). So, I tried lower symmetry space groups and I successfully solved the structure with a space group P21 (Rwork/Rfree: 0.22/0.27). However, there was one strange fact. The unit cell of the P21 was 104.209 104.225 104.254 90.000 89.967 90.000. I'm confused with this fact that a, b, and c of the unit cell are almost same, and in addition, the beta angle is too close to 90. I didn't do refinement with a twin option. So, is the space group correct? Is there anyone who know this case? Thanks, Sangheon Yu Rm. 1053 Bldg. 200 School of Agricultural Biotechnology College of Agriculture & Life Sciences Seoul National University Seoul 151-921, KOREA
