Inhibition of human arginase I by substrate and product analogues

Human arginase I is a binuclear manganese metalloenzyme that catalyzes the hydrolysis of l-arginine to generate l-ornithine and urea. We demonstrate that N-hydroxy-l-arginine (NOHA) binds to this enzyme with Kd = 3.6 μM, and nor-N-hydroxy-l-arginine (nor-NOHA) binds with Kd = 517 nM (surface plasmon resonance) or Kd ≈ 50 nM (isothermal titration calorimetry). Crystals of human arginase I complexed with NOHA and nor-NOHA afford 2.04 and 1.55 Å 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 l-lysine (Kd = 13 μM) is reported at 1.90 Å resolution. This structure confirms the importance of hydrogen bond interactions with inhibitor α-carboxylate and α-amino groups as key specificity determinants of amino acid recognition in the arginase active site.