title: Crystallographic studies of movement within proteins.
abstract: The primary results of X-ray diffraction studies of crystalline proteins are maps, showing the distribution of electron density within the crystals, from which the structures of the protein molecules can be determined. Improved descriptions of the molecular structures are obtained in a second stage of the analysis in which the molecular parameters are refined in such a way that the X-ray data predicted from the structure agree as closely as possible with those observed. The refined molecular model obtained in this way takes account of the mobility of the structure by attributing to each atom a parameter defining its apparent mean-square amplitude of vibration. This apparent motion of the atoms may be real or may arise because different molecules in the crystals adopt slightly different conformations or orientations. Studies at different temperatures help to resolve this ambiguity. The parameters describing the apparent motion of the atoms are also sensity to errors in the experimental data. Parallel studies of lysozymes from two different species have suggested strongly, however, that the X-ray data describe a characteristic property of the lysozyme molecule which is related to its activity. Preliminary studies of triose phosphate isomerase suggest that intramolecular motion and conformational variability play an important part in the activity of this enzyme.
mesh_terms: D001665:Binding Sites; D004099:Dihydroxyacetone Phosphate / Q000378:metabolism; D005986:Glyceraldehyde 3-Phosphate / Q000378:metabolism; D006358:Hot Temperature; D008958:Models, Molecular; D009113:Muramidase; D011487:Protein Conformation; D011506:Proteins; D014305:Triose-Phosphate Isomerase / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D011506:Proteins; D005986:Glyceraldehyde 3-Phosphate; D004099:Dihydroxyacetone Phosphate; D009113:Muramidase; D014305:Triose-Phosphate Isomerase