Inhibitor Coordination Interactions in the Binuclear Manganese Cluster of Arginase

• Published in: Biochemistry (Easton) 2004-07, Vol.43 (28), p.8987-8999
• Main Authors: Cama, Evis, Pethe, Stéphanie, Boucher, Jean-Luc, Han, Shoufa, Emig, Frances A, Ash, David E, Viola, Ronald E, Mansuy, Daniel, Christianson, David W
• Format: Article
• Language: English
• Subjects: Animals; Arginase - antagonists & inhibitors; Arginase - chemistry; Arginine - analogs & derivatives; Arginine - chemistry; Binding Sites; Crystallography, X-Ray; Enzyme Inhibitors - chemistry; Fluorine - chemistry; Hydrogen Bonding; Manganese; Metalloproteins - antagonists & inhibitors; Metalloproteins - chemistry; Molecular Structure; Protein Binding; Rats; Recombinant Proteins; Valine - chemistry
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi0491705

Arginase is a manganese metalloenzyme that catalyzes the hydrolysis of l-arginine to form l-ornithine and urea. The structure and stability of the binuclear manganese cluster are critical for catalytic activity as it activates the catalytic nucleophile, metal-bridging hydroxide ion, and stabilizes the tetrahedral intermediate and its flanking states. Here, we report X-ray structures of a series of inhibitors bound to the active site of arginase, and each inhibitor exploits a different mode of coordination with the Mn2+ 2 cluster. Specifically, we have studied the binding of fluoride ion (F-; an uncompetitive inhibitor) and l-arginine, l-valine, dinor-N ω-hydroxy-l-arginine, descarboxy-nor-N ω-hydroxy-l-arginine, and dehydro-2(S)-amino-6-boronohexanoic acid. Some inhibitors, such as fluoride ion, dinor-N ω-hydroxy-l-arginine, and dehydro-2(S)-amino-6-boronohexanoic acid, cause the net addition of one ligand to the Mn2+ 2 cluster. Other inhibitors, such as descarboxy-nor-N ω-hydroxy-l-arginine, simply displace the metal-bridging hydroxide ion of the native enzyme and do not cause any net change in the metal coordination polyhedra. The highest affinity inhibitors displace the metal-bridging hydroxide ion (and sometimes occupy a Mn2+ A site found vacant in the native enzyme) and maintain a conserved array of hydrogen bonds with their α-amino and -carboxylate groups.