title: Structure of activated aconitase: formation of the [4Fe-4S] cluster in the crystal.
abstract: The structure of activated pig heart aconitase [citrate(isocitrate) hydro-lyase, EC 4.2.1.3] containing a [4Fe-4S] cluster has been refined at 2.5-A resolution to a crystallographic residual of 18.2%. Comparison of this structure to the recently determined 2.1-A resolution structure of the inactive enzyme containing a [3Fe-4S] cluster, by difference Fourier analysis, shows that upon activation iron is inserted into the structure isomorphously. The common atoms of the [3Fe-4S] and [4Fe-4S] cores agree within 0.1 A; the three common cysteinyl S gamma ligand atoms agree within 0.25 A. The fourth ligand of the Fe inserted into the [3Fe-4S] cluster is a water or hydroxyl from solvent, consistent with the absence of a free cysteine ligand in the enzyme active site cleft and the isomorphism of the two structures. A water molecule occupies a similar site in the crystal structure of the inactive enzyme.
authors.affiliation: Department of Molecular Biology, Research Institute of Scripps Clinic, La Jolla, CA 92037.
authors.forename: A H
authors.initials: AH
authors.lastname: Robbins
authors.forename: C D
authors.initials: CD
authors.lastname: Stout
mesh_terms: D000154:Aconitate Hydratase; D000818:Animals; D001665:Binding Sites; D004789:Enzyme Activation; D007506:Iron-Sulfur Proteins / Q000648:ultrastructure*; D008667:Metalloproteins / Q000648:ultrastructure*; D008958:Models, Molecular; D009206:Myocardium / Q000201:enzymology; D011487:Protein Conformation; D013552:Swine; D014961:X-Ray Diffraction
chemical_list: D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D000154:Aconitate Hydratase