Crystal structures of zinc-free and -bound heme domain of human inducible nitric-oxide synthase. Implications for dimer stability and comparison with endothelial nitric-oxide synthase.
The crystal structures of the heme domain of human inducible nitric-oxide synthase (NOS-2) in zinc-free and -bound states have been solved. In the zinc-free structure, two symmetry-related cysteine residues form a disulfide bond. In the zinc-bound state, these same two cysteine residues form part of a zinc-tetrathiolate (ZnS(4)) center indistinguishable from that observed in the endothelial isoform (NOS-3). As in NOS-3, ZnS(4) plays a key role in stabilizing intersubunit contacts and in maintaining the integrity of the cofactor (tetrahydrobiopterin) binding site of NOS-2. A comparison of NOS-2 and NOS-3 structures illustrates the conservation of quaternary structure, tertiary topology, and substrate and cofactor binding sites, in addition to providing insights on isoform-specific inhibitor design. The structural comparison also reveals that pterin binding does not preferentially stabilize the dimer interface of NOS-2 over NOS-3.
Li
H
H
Department of Molecular Biology and Biochemistry, University of California at Irvine, Irvine, California 92697, USA.
Raman
C S
CS
Glaser
C B
CB
Blasko
E
E
Young
T A
TA
Parkinson
J F
JF
Whitlow
M
M
Poulos
T L
TL
D019281:Dimerization; D006418:Heme; D006801:Humans; D019001:Nitric Oxide Synthase / Q000737:chemistry*; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D011487:Protein Conformation; D015032:Zinc
D006418:Heme; C496319:NOS2 protein, human; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D015032:Zinc