title: Structural transitions in crystals of native aspartate carbamoyltransferase.
abstract: Screened precession x-ray photographs of crystals of native aspartate carbamoyltransferase (EC 2.1.3.2, from Escherichia coli) ligated with L-aspartate and phosphate reveal the presence of a crystal unit-cell dimension that is intermediate between the T (tense) and R (relaxed) states. Characterizing the intermediate (I) crystal is a c-axis unit-cell dimension of 149 A, halfway between the c-axis length of the T (c = 142 A) and R (c = 156 A) states, in the space group P321. Preservation of the P321 space group indicates that the intermediate crystal form retains a threefold axis of symmetry, and therefore the enzyme has at minimum a threefold axis; however, we do not know whether the molecular twofold axis is conserved. The I crystals are formed by soaking T-state crystals with L-aspartate and phosphate. By raising the concentration of L-aspartate we can further transform the I crystals, without fragmentation, to a form that has the same unit-cell dimensions as R-state crystals grown in the presence of N-(phosphonoacetyl)-L-aspartate.
authors.affiliation: Gibbs Chemical Laboratory, Harvard University, Cambridge, MA 02138.
authors.forename: J E
authors.initials: JE
authors.lastname: Gouaux
authors.forename: W N
authors.initials: WN
authors.lastname: Lipscomb
mesh_terms: D001221:Aspartate Carbamoyltransferase / Q000378:metabolism*; D003460:Crystallization; D004926:Escherichia coli / Q000201:enzymology; D046911:Macromolecular Substances; D008958:Models, Molecular; D008962:Models, Theoretical; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D046911:Macromolecular Substances; D001221:Aspartate Carbamoyltransferase