Chapter 18.3 Structure quality and target parameters

Crystallography of biological macromolecules

Second Online Edition (2012)

Part 18. Refinement

  1. R. A. Engh1,
  2. R. Huber2

Published Online: 14 APR 2012

DOI: 10.1107/97809553602060000857

International Tables for Crystallography

International Tables for Crystallography

How to Cite

Engh, R. A. and Huber, R. 2012. Structure quality and target parameters. International Tables for Crystallography. F:18:18.3:474–484.

Author Information

  1. 1

    Pharmaceutical Research, Roche Diagnostics GmbH, Max Planck Institut für Biochemie, 82152 Martinsried, Germany

  2. 2

    Max-Planck-Institut für Biochemie, 82152 Martinsried, Germany

Publication History

  1. Published Online: 14 APR 2012


Because protein crystals typically diffract to resolutions of 2–3 Å for structures of interest, diffraction data must be supplemented by additional information to be used as parameters for modelling the crystal content. Which information to use, and for what kind of model, depends on the questions to be resolved by the modelled structure. The most obvious choice for target parameters are bond lengths and angles derived from atomic resolution structures. This article describes a set of bond and angle target parameters derived from small-molecule structures in the Cambridge Structural Database and their application to the refinement of protein structure models. Other potential sources of target parameters are also briefly discussed.


  • bias;
  • bond-angle restraints;
  • bond-length restraints;
  • cross validation;
  • force constants;
  • nonbonded interactions;
  • outliers;
  • planarity restraints;
  • refinement;
  • restraints;
  • target parameters;
  • torsion-angle restraints