Solution H-1 NMR of the active site of substrate-bound, cyanide-inhibited human heme oxygenase - Comparison to the crystal structure of the water-ligated form

University of California, Department of Chemistry, Davis, California 95616, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 06/2001; 276(19):15676-87. DOI: 10.1074/jbc.M009974200
Source: PubMed


The majority of the active site residues of cyanide-inhibited, substrate-bound human heme oxygenase have been assigned on
the basis of two-dimensional NMR using the crystal structure of the water-ligated substrate complex as a guide (Schuller,
D. J., Wilks, A., Ortiz de Montellano, P. R., and Poulos, T. L. (1999) Nat. Struct. Biol. 6, 860–867). The proximal helix and the N-terminal portion of the distal helix are found to be identical to those in the
crystal except that the heme for the major isomer (∼75–80%) in solution is rotated 180° about the α-γ-meso axis relative to the unique orientation in the crystal. The central portion of the distal helix in solution is translated
slightly over the heme toward the distal ligand, and a distal four-ring aromatic cluster has moved 1–2 Å closer to the heme,
which allows for strong hydrogen bonds between the hydroxyls of Tyr-58 and Tyr-137. These latter interactions are proposed
to stabilize the closed pocket conducive to the high stereospecificity of the α-meso ring opening. The determination of the magnetic axes, for which the major axis is controlled by the Fe-CN orientation, reveals
a ∼20° tilt of the distal ligand from the heme normal in the direction of the α-meso bridge, demonstrating that the close placement of the distal helix over the heme exerts control of stereospecificity by both
blocking access to the β, γ, and δ-meso positions and tilting the axial ligand, a proposed peroxide, toward the α-meso position.

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