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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 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
>
>
