Inhibition of human arginase I by substrate and product analogues

Human arginase I is a binuclear manganese metalloenzyme that catalyzes the hydrolysis of t-arginine to generate L-ornithine and urea. We demonstrate that N-hydroxy-t-arginine (NOHA) binds to this enzyme with K-d = 3.6 mu M, and nor-N-hydroxy-L-arginine (nor-NOHA) binds with K-d = 517 nM (surface plasmon resonance) or K-d approximate to 50 nM (isothermal titration calorimetry). Crystals of human arginase I complexed with NOHA and nor-NOHA afford 2.04 and 1.55 angstrom resolution structures, respectively, which are significantly improved in comparison with previously-determined structures of the corresponding complexes with rat arginase I. Higher resolution structures clarify the binding interactions of the inhibitors. Finally, the crystal structure of the complex with t-lysine (K-d = 13 mu M) is reported at 1.90 angstrom resolution. This structure confirms the importance of hydrogen bond interactions with inhibitor alpha-carboxylate and alpha-amino groups as key specificity determinants of amino acid recognition in the arginase active site. (C) 2010 Elsevier Inc. All rights reserved.