Solution 1H NMR of the active site of substrate-bound, cyanide-inhibited human heme oxygenase. comparison to the crystal structure of the water-ligated form.
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 ( approximately 75-80%) in solution is rotated 180 degrees about the alpha-gamma-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 A 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 alpha-meso ring opening. The determination of the magnetic axes, for which the major axis is controlled by the Fe-CN orientation, reveals a approximately 20 degrees tilt of the distal ligand from the heme normal in the direction of the alpha-meso bridge, demonstrating that the close placement of the distal helix over the heme exerts control of stereospecificity by both blocking access to the beta, gamma, and delta-meso positions and tilting the axial ligand, a proposed peroxide, toward the alpha-meso position.
La Mar
G N
GN
University of California, Department of Chemistry, Davis, California 95616, USA.
Asokan
A
A
Espiritu
B
B
Yeh
D C
DC
Auclair
K
K
Ortiz De Montellano
P R
PR
D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D003486:Cyanides / Q000494:pharmacology*; D006418:Heme / Q000737:chemistry / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing) / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D006859:Hydrogen; D006860:Hydrogen Bonding; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D017433:Protein Structure, Secondary; D014443:Tyrosine; D014867:Water
D003486:Cyanides; D014867:Water; D014443:Tyrosine; D006418:Heme; D006859:Hydrogen; D006419:Heme Oxygenase (Decyclizing)