Structure quality and target parameters

Because protein crystals typically diffract to resolutions of 2–3 A 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.

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