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Re: [ccp4bb]: Twinning/Merging
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----- Original Message -----
From: "Rizkallah, PJ (Pierre)" <P.J.Rizkallah@dl.ac.uk>
To: "'Daniel Schlieper'" <Daniel.Schlieper@Uni-Koeln.DE>
Cc: <ccp4bb@dl.ac.uk>
Sent: Friday, December 15, 2000 6:11 PM
Subject: RE: [ccp4bb]: Twinning/Merging
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>
> Hi there,
>
> There are many reasons other than twinning to explain the high R-merge:
> 1- The space group reported is enantiomeric. When you have 3 different
> xtals,
> you must make sure they all have the same hand. How do you find out? In
the
> merging stats you will see R-syms (R-merge for the equivalents in one
image)
> for the images from one xtal worse than the others. This is a clear
> giveaway,
> which you must check.
If all three crystals are isomorphous and contain the same enantiomeric
molecules (which is the case with natural/overexpressed proteins) then there
would be no reason to assume, that one of the crystals could have the
opposite hand. If I may cite C. Giacovazzo: "The 230 space groups include 11
enantiomorphous pairs: P31 (P32),...,P4132 (P4332). The (+) isomer of an
optically active molecule crystallizes in one ot the two enantiomorphous
space groups, the (-) isomer will crystallize in the other.", from
"Fundamentals of Crystallography", by Giacovazzo et al., page 25, IUCR Texts
on Crystallography 2, Oxford University Press, reprinted 1998.
With kind regards,
Dirk Kostrewa.
***************************************************************
Dirk Kostrewa
Paul Scherrer Institut e-mail: dirk.kostrewa@psi.ch
Life Sciences phone: +41-56-310-4722
OSRA/007 fax: +41-56-310-4556
CH-5232 Villigen PSI WWW: www.sb.psi.ch
Switzerland
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