Re: [ccp4bb]: ligands in a 2-fold axis

[Luca Jovine <lucajovine@mac.com>]

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Hi Rongsheng,

For yet another related case, see Structure 8:527-540 (2000) - what we had 
was a crystal contact consisting of 5 stacked nucleotides, with "outer" 
nucleotides 1,2 and 1',2' coming from two symmetry-related molecules, and 
the central position corresponding to nucleotides 3 and 3' that overlapped 
on a two-fold axis (i.e. 1 - 2 - 3/3' - 2' - 1').
What we also did (with CNS) was to refine the central nucleotide sitting 
on the two-fold axis with half occupancy, since, in order to make physical 
sense, it must have locally broken crystallographic symmetry by being in 
alternatively ordered and disordered conformation in adjacent molecules.
Hope this helps,

Luca

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Luca Jovine, Ph.D.
Department of Molecular, Cell & Developmental Biology
Mount Sinai School of Medicine
Annenberg Building, Room 25-18
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E-Mail: lucajovine@mac.com - luca.jovine@mssm.edu
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