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Background: The quality of X-ray crystallographic models for biomacromolecules refined from data obtained at high-resolution is assured by the data itself. However, at low-resolution, >3.0 AÅ, additional information is supplied by a forcefield coupled with an associated refinement protocol. These resulting structures are often of lower quality and thus unsuitable for downstream activities like structure-based drug discovery. Methodology: An X-ray crystallography refinement protocol that enhances standard methodology by incorporating energy terms from the HINT (Hydropathic INTeractions) empirical forcefield is described. This protocol was tested by refining synthetic low-resolution structural data derived from 25 diverse high-resolution structures, and referencing the resulting models to these structures. The models were also evaluated with global structural quality metrics, e.g., Ramachandran score and MolProbity clashscore. Three additional structures, for which only low-resolution data are available, were also re-refined with this methodology. Results: The enhanced refinement protocol is most beneficial for reflection data at resolutions of 3.0 Å or worse. At the low-resolution limit, $4.0 Å, the new protocol generated models with Ca positions that have RMSDs that are 0.18 Å more similar to the reference high-resolution structure, Ramachandran scores improved by 13%, and clashscores improved by 51%, all in comparison to models generated with the standard refinement protocol. The hydropathic forcefield terms are at least as effective as Coulombic electrostatic terms in maintaining polar interaction networks, and significantly more effective in maintaining hydrophobic networks, as synthetic resolution is decremented. Even at resolutions $4.0 Å, these latter networks are generally native-like, as measured with a hydropathic interactions scoring tool. [ABSTRACT FROM AUTHOR]

The article describes three-dimensional (3D) reconstruction of the v-AlCrFe phase by electron crystallography. High-resolution transmission-electron microscopy (HREM) images and selected-area electron diffraction patterns from 13 different zone axes were combined to give a 3D potential map. Electron crystallography is a powerful method for solving structures of crystals with submicrometre sizes, which are too small for X-ray crystallography. 3D reconstruction from HREM images offers a new possibility for ab initio structure determination of inorganic compounds existing only with very small crystal sizes.