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Acta Crystallogr D Biol Crystallogr. 2007 Jan;63(Pt 1):58-61. Epub 2006 Dec 13.

An introduction to stereochemical restraints.

Author information

  • 1MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, England. pre@mrc-lmb.cam.ac.uk

Abstract

At the resolution available from most macromolecular crystals, the X-ray data alone are insufficient to lead to a chemically reasonable structure, so stereochemical restraints are essential. These usually restrain bond lengths, bond angles, planes and chiral volumes. The definition of these restraints and where the values come from are described. A dictionary entry contains information about the atom types, their connectivity and all the appropriate restraints. Torsion angles are not usually restrained, but they do have optimum values. In the special case of flexible five- and six-membered rings, including pentose and hexose sugars, the ring pucker is defined by combinations of torsion angles and the pucker affects the position of substituents.

PMID:
17164527
PMCID:
PMC2483478
DOI:
10.1107/S090744490604604X
[PubMed - indexed for MEDLINE]
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