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Hi Natesh Yeates TO, Fam BC. Related Articles, Links Protein crystals and their evil twins. Structure. 1999 Feb 15;7(2):R25-9. Review. Yeates TO. Related Articles, Links Detecting and overcoming crystal twinning. Methods Enzymol. 1997;276:344-58. PMID: 9048378 [PubMed - indexed for MEDLINE] Also for this specific case Eleanor Dodsons' 2005 post and related items may be helpful. http://www.mail-archive.com/[email protected]/msg00947.html J Ramanathan NATESH <[EMAIL PROTECTED]> wrote: > *** For details on how to be removed from this list visit the *** > *** CCP4 home page http://www.ccp4.ac.uk *** > > > Dear All, > > Could anyone please point me to similar references for P61/P6122 > twinning issues, on similar lines suggested for P21/C2221 by James ? > > Thanks in advance. > > natesh > > R. Natesh > IGBMC > > On Tue, 23 May 2006, James Whisstock wrote: > > > *** 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 issueand > 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 > > > > >
