Hi Sangheon As others have said, there is nothing that stops a cell being monoclinic with those cell dimensions - indeed, there is nothing stopping it being triclinic, orthorhombic or tetragonal either (or even rhombohedral, for those of us who like to describe it with non-hexagonal axes).
What *is* important is the symmetry of the reciprocal lattice; looking at projections of the reciprocal lattice along the major axes (i.e. a*, b* or c*) using a tool like hklview or viewhkl (both of which are in ccp4 6.4.0) should be sufficient to demonstrate whether you really have the higher symmetry. On 25 Oct 2013, at 01:55, 유상헌 wrote: > 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 > > Harry -- ** note change of address ** Dr Harry Powell, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH Chairman of European Crystallographic Association SIG9 (Crystallographic Computing)
