PDBsum entry 1lzx

Oxidoreductase

PDB id: 1lzx

Contents

Protein chains

407 a.a. *

Ligands

ACT ×2

HEM ×2

H4B ×2

HAR ×2

Metals

_ZN

Waters ×469

* Residue conservation analysis

References listed in PDB file

Key reference

Title

The novel binding mode of n-Alkyl-N'-Hydroxyguanidine to neuronal nitric oxide synthase provides mechanistic insights into no biosynthesis.

Authors

H.Li, H.Shimizu, M.Flinspach, J.Jamal, W.Yang, M.Xian, T.Cai, E.Z.Wen, Q.Jia, P.G.Wang, T.L.Poulos.

Ref.

Biochemistry, 2002, 41, 13868-13875. [DOI no: 10.1021/bi020417c]

PubMed id

12437343

Abstract

A series of N-alkyl-N'-hydroxyguanidine compounds have recently been characterized as non-amino acid substrates for all three nitric oxide synthase (NOS) isoforms which mimic NO formation from N(omega)-hydroxy-L-arginine. Crystal structures of the nNOS heme domain complexed with either N-isopropyl-N'-hydroxyguanidine or N-butyl-N'-hydroxyguanidine reveal two different binding modes in the substrate binding pocket. The binding mode of the latter is consistent with that observed for the substrate N(omega)-hydroxy-L-arginine bound in the nNOS active site. However, the former binds to nNOS in an unexpected fashion, thus providing new insights into the mechanism on how the hydroxyguanidine moiety leads to NO formation. Structural features of substrate binding support the view that the OH-substituted guanidine nitrogen, instead of the hydroxyl oxygen, is the source of hydrogen supplied to the active ferric-superoxy species for the second step of the NOS catalytic reaction.

Secondary reference #1

Title

Crystal structure of constitutive endothelial nitric oxide synthase: a paradigm for pterin function involving a novel metal center.

Authors

C.S.Raman, H.Li, P.Martásek, V.Král, B.S.Masters, T.L.Poulos.

Ref.

Cell, 1998, 95, 939-950. [DOI no: 10.1016/S0092-8674(00)81718-3]

PubMed id

9875848

Figure 5.
Figure 5. Cooperativity and Molecular Mimicry in eNOS(A) Cross talk between H[4]B and L-Arg mediated by the heme propionate (Se-edge data). The guanidinium and amino groups of L-Arg are held in place by H-bonding with the conserved Glu-363. The amino group also H-bonds with a heme propionate. H[4]B H-bonds directly with the heme propionate, while the pteridine ring is sandwiched between Phe-462 in one monomer and Trp-449 in another, respectively.(B) L-Arg is a structural mimic of H[4]B at the pterin-binding site when SEITU is bound at the active site (-H[4]B, +SEITU data). L-Arg binds to the pterin site and exquisitely mimics the H[4]B interaction with eNOS ([A] and Figure 4). The specific interaction of the potent inhibitor, SEITU, at the active site is mediated by a pair of bifurcated H-bonds to Glu-363. Two water molecules bridge between the inhibitor and heme propionate. The ethyl group of the inhibitor forms nonbonded contacts with Val-338 and Phe-355. The ureido sulfur is positioned 3.5 Å and 4.0 Å above heme pyrrole B-ring nitrogen and the heme iron, respectively.

Figure 7.
Figure 7. Proposed Mechanism for Pterin in NO BiosynthesisThe uniqueness of the H[4]B–eNOS interaction (Figure 4) and the ability to bind L-Arg at the pterin site present a strong case for the involvement of a pterin radical in NOS catalysis and rule out the possibility of H[4]B ↔ qH[2]B cycling during NO biosynthesis. R represents the dihydroxypropyl side chain at the C6 position on the pterin ring.

The above figures are reproduced from the cited reference with permission from Cell Press