Structure of Activated Aconitase: Formation of the [4Fe-4S] Cluster in the Crystal

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 86; no. 10; pp. 3639 - 3643
• Main Authors: Robbins, A. H., Stout, C. D.
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 01.05.1989; National Acad Sciences
• Subjects: Aconitate Hydratase; Active sites; Animals; Atoms; Binding Sites; Biological and medical sciences; Crystal structure; Crystalline structure; Crystals; Electron density; Enzyme Activation; Enzymes; Fundamental and applied biological sciences. Psychology; heart; Iron-Sulfur Proteins - ultrastructure; Ligands; Metalloproteins - ultrastructure; Models, Molecular; Molecular biophysics; Molecular structure; Molecules; Myocardium - enzymology; pigs; Protein Conformation; Proteins; Structure in molecular biology; Swine; X-Ray Diffraction; Heart; Vertebrata; Mammalia; Enzyme; Artiodactyla; Aconitate hydratase; X ray diffraction; Ungulata; Iron Sulfur cluster; Pig; Crystalline structure
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.86.10.3639

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- angstrom resolution to a crystallographic residual of 18.2%. Comparison of this structure to the recently determined 2.1- angstrom 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 angstrom; the three common cysteinyl Sγligand atoms agree within 0.25 angstrom. 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.