Structural basis for pterin antagonism in nitric-oxide synthase: Development of novel 4-oxo-pteridine antagonists of (6R)-5,6,7,8-tetrahydrobiopterin

Academic Article

Abstract

  • Pathological nitric oxide (NO) generation in sepsis, inflammation, and stroke may be therapeutically controlled by inhibiting NO synthases (NOS). Here we targeted the (6R)-5,6,7,8-tetrahydro-L-biopterin (H4Bip)-binding site of NOS, which, upon cofactor binding, maximally increases enzyme activity and NO production from substrate L-arginine. The first generation of H 4Bip-based NOS inhibitors employed a 4-amino pharmacophore of H 4Bip analogous to antifolates such as methotrexate. We developed a novel series of 4-oxo-pteridine derivatives that were screened for inhibition against neuronal NOS (NOS-I) and a structure-activity relationship was determined. To understand the structural basis for pterin antagonism, selected derivatives were docked into the NOS pterin binding cavity. Using a reduced 4-oxo-pteridine scaffold, derivatives with certain modifications such as electron-rich aromatic phenyl or benzoyl groups at the 5- and 6-positions, were discovered to markedly inhibit NOS-I, possibly due to hydrophobic and electrostatic interactions with Phe462 and Ser104, respectively, within the pterin binding pocket. One of the most effective 4-oxo compounds and, for comparisons an active 4-amino derivative, were then co-crystallized with the endothelial NOS (NOS-III) oxygenase domain and this structure solved to confirm the hypothetical binding modes. Collectively, these findings suggest (i) that, unlike the antifolate principle, the 4-amino substituent is not essential for developing pterin-based NOS inhibitors and (ii), provide a steric and electrostatic basis for their rational design.
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    Author List

  • Kotsonis P; Fröhlich LG; Raman CS; Li H; Berg M; Gerwig R; Groehn V; Kang Y; Al-Masoudi N; Taghavi-Moghadam S
  • Start Page

  • 49133
  • End Page

  • 49141
  • Volume

  • 276
  • Issue

  • 52