Abstract
Crystal structures of human endothelial nitric oxide synthase (eNOS) and human inducible NOS (iNOS) catalytic domains were solved in complex with the arginine substrate and an inhibitor S-ethylisothiourea (SEITU), respectively. The small molecules bind in a narrow cleft within the larger active-site cavity containing heme and tetrahydrobiopterin. Both are hydrogen-bonded to a conserved glutamate (eNOS E361, iNOS E377). The active-site residues of iNOS and eNOS are nearly identical. Nevertheless, structural comparisons provide a basis for design of isozyme-selective inhibitors. The high-resolution, refined structures of eNOS (2.4 Å resolution) and iNOS (2.25 Å resolution) reveal an unexpected structural zinc situated at the intermolecular interface and coordinated by four cysteines, two from each monomer.
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Acknowledgements
We thank G. Hammond for technical assistance, C. Eckhart for carrying the atomic absorption experiments, Y.-H. Liu and B. Pramanik for the mass spectrometry analyses, and G. Bricogne, P. Reversi and C. Strickland for helpful discussions.
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Fischmann, T., Hruza, A., Niu, X. et al. Structural characterization of nitric oxide synthase isoforms reveals striking active-site conservation. Nat Struct Mol Biol 6, 233–242 (1999). https://doi.org/10.1038/6675
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DOI: https://doi.org/10.1038/6675
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