*** For details on how to be removed from this list visit the *** *** CCP4 home page http://www.ccp4.ac.uk ***
Hi David - Check out Yang F, Dauter Z, Wlodawer A. Effects of crystal twinning on the ability to solve a macromolecular structure using multiwavelength anomalous diffraction. Acta Crystallogr D Biol Crystallogr. 2000 Aug;56(Pt 8):959-64. PMID: 10944332 [PubMed - indexed for MEDLINE] and Ban N, Nissen P, Hansen J, Capel M, Moore PB, Steitz TA. Placement of protein and RNA structures into a 5 A-resolution map of the 50S ribosomal subunit. Nature. 1999 Aug 26;400(6747):841-7. and related papers Which provides a nice description of the P21 / C2221 twinning issue and also some ways of resolving it. J Eleanor Dodson <[EMAIL PROTECTED]> wrote: > In this space group with |a| ~ equal |c| you could have a twinning > matrix l.-k,h > You should have been offered the possibility of processing the data with > point group Cmmm > did that give a reasonable Rsym? > > And you would expect to see some 2 fold symmetry in the h0l h1l etc > sections - look at these with hklview. > > The newest SFCHECK will also do a twinning test with the above operator > Eleanor > > > David Schwefel wrote: > > >*** For details on how to be removed from this list visit the *** > >*** CCP4 home page http://www.ccp4.ac.uk *** > > > > > >Hi there! > >I have a problem during refinement of apparently good data... > >the protein crystallised in space group P21 with following cell parameters: > >44.5 86.5 44.6 90 112.5 90 > >the crystal diffracted up to 1.5 A and the diffraction pattern looked very > >good > > > >some statistics from the CORRECT.LP: > > > >Res. Range I/sigma(I) Chi² R obs R exp refl. accepted rej. > >43.162 1.498 8.56 1.00 4.91 5.35 139902 138325 750 > > > >after Molrep, rigid body and restrained refinement with ccp4, the R factor > >is still around 40 % and won't go further down, and there are some regions > >where the density looks really bad... > >I read that twinning could be an explanation so i checked <I²>/<I>² which > >ranges from 1.75 to 2 depending on the resolution, which means that the > >crystal is twinned. > >As far as I understood is it possible to detwin the data if you know the > >symmetry between and the relative fractions of the twin domains, but I only > >found possible twin laws for higher symmetry crystals. > >Has anyone a clue or some reference how to proceed with this data (which > >looked so fine in the beginning...)? > > > >thanks in advance, > >David > > > > > > > > > > > --------------- > > Attachment: ccp4.vcf > MIME Type: text/x-vcard > Size: 208 bytes
